Your Cart

Chapter 9 Digestion and Absorption by TEACHING CARE online tuition and coaching classes

Chapter 9 Digestion and Absorption by TEACHING CARE online tuition and coaching classes



Animals are not able to synthesise their own food, therefore they depend on ready-made food for their nutritional requirements. The term nutrition refers to the sum total of all the processes related with the conversion of the raw foodstuff into the stuff of the body to supply energy for different metabolic activities and also for the repair and growth. In other word we can define nutrition as the process by which an organism derives energy to work and other materials, required for growth and maintenance of the various activities of life.

Food intake : Different organisms obtain food in different ways but carry out similar chemical reactions to utilize it. To take food, protozoans use pseudopodia, flagella or cilia; sponges and mussels, a current of water; Hydra, tentacles beset with stinging cells; planarians and earthworms, a muscular pharynx; flukes and leeches, oral sucker; insects and other arthropods, mouth parts of various kinds; and seastars and sea urchins, tubefeet. Sharks capture prey with the jaws; frog and lizard with the tongue; birds with beaks of sorts; rabbit and hare use forepaws, lips and teeth; cattle, lips and teeth; carnivores, claws and teeth; giraffes, tongue; elephants, proboscis (trunk); humans, monkeys and apes use hands.


The process by which complex food is converted into simplest food with the help of digestive enzymes (Hydrolytic enzymes), hence process of digestion is a hydrolytic process.

Types of digestion

  • Intracellular : When the process of digestion occurs within the cell in the food vacuole. Examples : Protozoa, Porifera, Coelenterata and free living With the help of lysosomal enzymes. Food particle is taken in through endocytosis (phagocytosis). It forms a phagosome which fuses with a lysosome. Digestion occurs and the digested materials are passed on to cytoplasm. The undigested materials is thrown out by exocytosis.
  • Extracellular : When the process of digestion occurs outside the cell. Examples : Coelenterates and phylum platyhelminthes to phylum Therefore, coelenterata and free living platyhelminthes (flat worms) perform both intracellular and extracellular digestion.

 Digestive system of human.

Digestion in vertebrates occurs in the digestive tract or alimentary canal. The various parts involved in digestion can be broadly grouped in two groups –

(i)  Digestive tract or alimentary canal

  • Digestive glands

(i) Digestive tract or alimentary canal

On the basis of the embryonic origin, the alimentary canal of vertebrates can be divided into three parts

  • Fore gut / Stomodaeum : It includes buccal cavity / oral cavity.






  • Mid gut / Mesodaeum : It includes pharynx, oesophagus, stomach, small intestine, and large intestine.
  • Hind gut / Proctodaeum : It includes anal canal and anus.

Parts      of      alimentary     canal      and                             its histology


  • Mouth
  • Vestibule
  • Bucco-pharyngeal cavity
  • Oesophagus
  • Stomach
  • Small intestine consist of duodenum, jejunum, lleum
  • Large intestine consist of caecum, colon, rectum
  • Anal canal and anus
  • Generalized histology of alimentary canal
  • Mouth : The mouth is a transverse slit bounded by two movable lips or labia, upper lip and lower lip. Upper lip has small ridges on the sides, a tubercle in the middle and a vertical groove (philtrum)
  • Vestibule : It is a narrow space between








Gall bladder









































lips and gums in front and gums and cheeks on the

Alimentary canal of man


sides. Its lining contains mucous glands. In the vestibule, a small median fold of mucous membrane, the superior labial frenulum, connects the middle of the upper lip to the gum and usually a similar but smaller inferior labial frenulum connects the middle of the lower lip to the gum.

  • Buccopharyngeal cavity : It includes anterior buccal cavity lined by stratified squamous epithelial cell and posterior pharyngeal cavity lined by columnar epithelial cell. It is distinguished into three region. Pharynx is a vertical canal beyond the soft palate. The food and air passages cross here. Pharynx may be divided into three



Nasopharynx Oropharynx Laryngopharynx
Upper part of pharynx. Middle part of pharynx. Lower part of pharynx.
Lined    by    pseudostratified            columnar epithelium Lined by stratified squamous epithelium. Lined by columnar epithelium.
It has internal nares in the roof, a pair of openings of the eustachian tube on the sides leading to middle ear. Oral cavity open to it. It lead to oesophagus behind and larynx in front.
Lymphoid Pharyngeal tonsil (Adenoid) in the back wall of Nasopharynx. Lymphoid palatine tonsil lies on either side of the oropharynx between two vertical folds. Opening of oesophagus is called gullet and opening of larynx is called glottis. A cartilagenous flap epiglottis present in the front of glottis.



The various structure present in buccopharyngeal cavity are as follows –

(a) Fauces : A triangular area present between buccal cavity and pharynx in human.

  • Palate : The roof of buccal cavity is called Palate. In crocodiles and mammals horizontal shelf like processes of premaxilla and maxilla and the palatine bones of upper jaw fused and form a secondary palate. Which separates the buccal cavity from nasal cavity. Palate is distinguished into three regions –
  • Hard palate : Anterior, bony portion formed of maxilla and palatine bones in human and premaxilla, maxilla and palatine bones in Hard palate have































transverse ridges called

palatine rugae Such rugae or



ridges are more develop in carnivorous mammals because their function is to firmly grip the food and





prevent it from slipping out the cavity.

Fig. – The mouth and permanent dentition of a man


  • Soft palate : Posterior soft part, made up of connective tissue and
  • Vellum palate/uvula : Part of soft palate, which hangs in the region of pharynx. It closes the internal nostrils during
  • Palatine glands : Numerous mucous glands. Chiefly present in soft palate, secretes mucous for
  • Naso-palatine duct : One pair, present in rabbit, extends from nasal passage to the buccal passage, contains Jacobson’s organ concerned with
  • Vibrissae : A tuft of hairs on upper lip of
  • Hare-cleft : A cleft on the upper lip of rabbit, which makes it



  • Tongue (lingua) : Ectodermal, single, pinkish, oval, elongated highly muscular (mesodermal) and protrusible present on the floor of buccopharyngeal cavity the cells present are stratified squamous epithelial cells. A furrow termed the sulcus terminalis divides the oral part and pharyngeal part of the tongue. The limbs of the sulcus terminalis run laterally and forward from a median pit, named the foramen caecum.

Posterior part of tongue (endodermal) is attached with hyoid, middle one with the floor of buccopharyngeal cavity with the help of frenulum lingum and anterior part is free. The tongue is provided with two specialized structure viz. lingual papillae and lingual glands or weber’s gland. Lingual glands are the mucous glands, which secretes mucous. Lingual papillae are numerous, minute projections chiefly present on the dorsum of the tongue. All these lingual





































papillae can be grouped as simple lingual papillae and taste papillae. Taste papillae are of following types –

Locations of papillae and areas of taste on the tongue


  • Circumvallate : Circular largest 8-12 in number, present in the posterior part of the tongue extending from one side to They possess taste buds. These are the largest of all the papillae.
  • Fungiform : Mushroom shaped (Fungi – shaped), numerous, present at the anterior margins and tip of the tongue. They have taste
  • Foliate : Leaf like flat, less in number, present at the posterior margin of the They are absent/vestigeal in human.
  • Filliform : Conical shaped, smallest and most numerous distributed throughout They are without taste buds.


Hence, in human taste is recognized with the help of circumvallate and fungiform taste papillae. In man the anterior end of tongue feels sweet taste, posterior part feel bitter taste, sides feel sour taste and a small part behind the anterior end feel salty taste.

Functions of tongue : Important function of tongue are as follows –

  • Acts as universal toothbrush, as it helps in tooth cleaning.




















  • Helps in speaking.
  • Helps in degglutition.
  • Helps in mixing saliva with food.
  • Acts as a curry comb in many animals, hence help in body
  • Helps in taste detection.

Fig. – Dorsal surface of human tongue, showing four kinds of papillae and some other associated structures






  • In dog helps in regulation of body The phenomenon is called as “Panting”.
  • In frog and other animals, it helps in prey capturing
  • Teeth : Teeth is a living

(i)  On the basis of embryonic origin, teeth in vertebrates are of following two types –

  • Horny/ectodermal/epidermal/false teeth : The teeth which develops only from ectoderm. Examples – Cyclostomes, tadpole larva of frog, prototherian mammals
  • True teeth : The teeth which develops from both ectoderm and mesoderm. Examples – Fishes, amphibians, reptiles, eutherian mammals
    • Differentiation of teeth : Morphologically, teeth can be distinguished as homodont or
  • Homodont : When all the teeth are structurally and functionally Examples – Vertebrates except metatherian and eutherian mammals.
  • Heterodont : When the teeth are different in structure and functions. They are distinguished into four types incisors, canines, premolars and molars. Examples – metatherian and eutherian
    • Incisors : These are the front teeth borne by the premaxillae in upper jaw and tips of dentaries in lower They are single-rooted monocuspid and long, curved and sharp-edged. They are adapted for cutting or cropping and biting.
    • Canines : There is one pointed canine in each maxillary of upper jaw and each dentary of lower jaw next to the incisors. They are meant for piercing, tearing and offence and defence. They are single rooted and monocuspid.
    • Premolars : They have two roots and two cusps (bicuspid). They are meant for crushing, grinding and
    • Molars : They have more than two roots and 4-5
    • Attachment of teeth : On the basis of attachment of teeth at their bases with the jaw bones, teeth can be differentiated into –
  • Acrodont : Teeth are attached to the free surface or summit of the jaw bone, as in a shark or Such teeth are apt to break off easily but are replaced.
  • Pleurodont : In this condition, common in urodeles and lizards, teeth are attached to the inner side of jaw bone by their base as well as one
  • Thecodont : Such teeth are characteristic of mammals. Teeth have well developed roots implanted in deep individual pits or


socketes called alveoli or theca, in the jaw bone. These type of teeth also present in crocodilians, fossil toothed bird (Archeaeopteryx).


Fig. – Methods of attachment of teeth on jaws


  • Succession of teeth : According to their replacement (succession), teeth can be divided into 3 categories: polyphyodont, diphyodont and





  • Polyphyodont : In lower vertebrates, teeth can be replaced an indefinite number of times during e.g.
  • amphibia,
  • Diphyodont : In most mammals teeth develop during life in two successive sets, a condition known as diphyodont. Teeth of the first set are known as deciduous teeth or milk teeth or lacteal teeth whereas the second set is called permanent teeth.
  • Monophyodont : In some mammals such as platypus, marsupials, moles, sirenians, toothless whale only one set of teeth develops known as monophyodont condition.

Important Tips


  • Types of cheek teeth
  • Bunodont : Crown with small, blunt and round cusps as in man, monkey, pig found in mixed diet mammals.
  • Secodont : With sharp cutting edges for tearing flesh as in
  • Lophodont : With transverse ridges called lophos, g., Elephant.
  • Selenodont : With vertical crescentic cusps as in grazing mammals like cow, sheep and Selenodont teeth are two type –
    • Brachyodont : Normal low crowned selenodont teeth with short roots are termed e.g. Ground squirrel.
    • Hypsodont : In large grazing mammals teeth are elongated, prism shaped with high crown and low

e.g. Horse, cattle.

  • Structure of teeth : Teeth divided into three parts –
  • Root : Inner most attached to the bone with help of cement (hyaluronic acid).
  • Neck : Middle, small, covered with Gum provides strength to the teeth.
  • Apex or crown : External exposed part of Longest part, white in colour.



Teeth are made up of a hollow cavity, called as pulp cavity or dentine pulp cavity. It contains blood vessels lymphatic vessels nerve fibres, connective tissue etc. and provides nutrition to odontoblast cells or osteoblast cells. The odontoblast cells are mesodermal in embryonic origin forming immediate covering of the pulp cavity. The cells secrete dentine/ivory. Bulk of tooth in a mammal is formed of dentine. Dentine is a layer of inorganic substances (62-69%), which surrounds the odonto-blast cells. It is mesodermal in origin. Enamel, secreted by Ameloblast/Enameloblast cells, forms the outermost covering. It is ectodermal and made up of 92% of inorganic substances, hence considered as hardest part of the body. The inorganic substances present are [Ca3(PO4)2,Ca(OH)2.H2O] Calcium phosphate (85%), Calcium hydroxide and Calcium Carbonate.

Cement/Cementum attaches the tooth root to the bone. A thin peritoneal membrane is present between the two called as peridontal membrane or Sharpey’s fiber running from cement to bone. Gum is chiefly made up of connective tissue. In the incisors

























of rodents, lagomorphs and elephants, pulp cavity remains open

Fig. – Structure of tooth


basally so that these teeth continue to grow throughout life and are termed open-rooted. In the majority of mammals, including man, the basal aperture of pulp cavity becomes closed at a certain age so that nourishment stops and further growth ceases. Such teeth are termed close-rooted.

  • Odontogenesis : In mammals, teeth develop in the gum or the soft tissue covering the borders of premaxillae, maxillae and dentaries. Enamel of tooth is derived from epidermis, while the rest of tooth from dermis or In the beginning there is a thickening of ectoderm along the margin of Jaw bone. The basal layer of ectoderm, the Malpighian layer, forms a continuous solid ridge-like vertical invagination into the underlying dermis. This forms the dental lamina, which retains its connection with the outer epidermis.







































Fig. – Development of a mammalian tooth






Mesodermal cells multiply rapidly beneath the ectodermal ingrowth or dental lamina forming a series of solid bud-like outgrowths at intervals, called tooth germs. Their number is as many as the number of milk teeth. In each tooth germ, the inverted cup-like epithelial cap will secrete the enamel, hence termed the enamel organ. The mesodermal aggregation beneath enamel organ is termed dermal or dental papilla. Its outer columnar cells become differentiated into odontoblasts, which secrete a layer of dentine on their outer surface. The cells of inner epithelial layer of enamel organ similarly become ameloblasts, which form a cap of hard enamel around the top and sides of dentine. No enamel is deposited on the root. Dental papilla is retained as pulp. Its central cavity goes on increasing to become the pulp cavity. Nerves and blood vessels enter the pulp cavity through the basal opening. Upto this stage the tooth remains inside the tissue (gum). Later, its eruption through the overlying epidermis is known as cutting of tooth. Around the root of tooth appears cement or cementum, which is a modified bone. Odontoblasts become inactive when tooth is fully formed. However in rodents, lagomorphs, etc. the odontoblasts remain active throughout life and teeth continue to grow.














CAT              DOG         BEAR


















C                                               D





























UNWORN                      WORN


































Fig. – Modifications of cheek teeth. A – Carnassial teeth (secondont). B – Denticulate molar. C – Triconodont tooth. D – Tritubercular tooth showing arrangement of cusps. E – Bunodont molar in V.S. F – Brachodont selenodont molar. G – Surface view of crown of brachyodont molar. H – Sypsodont selenodont molars. I – Hypsodont teeth in

V.S. J – Lophodont molar.






  • Dental formula : Each mammalian species is characterized by its own specific dentition with a definite number and arrangement of teeth. Hence, dentition is of taxonomic importance. It is expressed by a dental formula as below –


Rabbit : i 2 , c 0 , pm 3 , m 3 = 8 ´ 2 = 28

or briefly,

23002 + 0 + 3 + 3 ´ 216 = 28


1    0       2     3    6

1023    1 + 0 + 2 + 3   2    12


(i = incisors; c = canines; pm = premolars; m = molars)

Dental formulae of some common mammals


Horse and pig = 44   Cat = 30  
Dog = 42   Squirrel = 22  
Lemur = 36   Rat = 16  
Man = 32   Elephant = 14  
Cow = 32   Permanent set milk set = 20  

Important Tips

  • Baleen – Whale bone whale have in the buccal cavity a special structure called baleen or whale It consists of several parallel horny plates hanging from the palate.
  • Cheek pouches – In some rodents (squirrel, rat) certain old world monkey, the vestibule extends to form cheek pouches for temporary storage of masticated
  • Taste buds contain group of sensory epithelial These cells are anteriorly provided with kinocilium and posteriorly with nerve fibres. The taste centres are present in brain.
  • Gustatoreceptor – The organ concerned with taste They are a type of chemoreceptor found in the parietal lobe of cerebrum.
  • In frog, tongue is anteriorly attached with the floor of buccopharyngeal cavity at lower jaw, whereas posterior end is free and
  • The tongue of snake is bifid and sensitive to odour and
  • Toothpaste protects the gum, whereas fluorides present in toothpaste clean the The excess of fluorides causes the disease fluorisis which leads to decaying of teeth and bones.
  • Elephant tusk is the upper
  • 3rd molar in human is called as wisdom teeth as arises after the age of 16-17 Wisdom teeth 4 in number.
  • Teeth of fishes are modified placoid
  • Teeth in frog are present only on upper
  • Caries Decay of teeth due to degeneration of enamel and formation of
  • Pyorrhoea infected gums and tooth
  • Maximum number of teeth present in opossum is 50 5134 =50 .


  • The number of teeth that grows once and twice in humans life is 12 and 20
  • Lophodont teeth in elephant are premolar and
  • Incisors of rats are
  • Teeth of sloths and armadillos have no
  • Enamel is lacking in the teeth of
  • Jacobson organ (Vomeronasal organs) – They are independent chambers below nasal cavities found in most tetrapods, although they are sometimes vestigial (like human). Absent in fish but occurs embryonic rudiments in most In reptiles, they are best developed in lizards, snakes and sphenodon but are absent in adult crocodiles. Jacobsons organ well developed in such animals that hold food in their mouth. This organ serve to smell food and recognize its chemical nature. They also help enemy recognition, locating members to opposite sex, courtship etc.






(d)  Oesophagus (food tube)

  • Morphology : Single, endodermal, dorsal to trachea, approximately 25-40 cm passes through thoracic cavity and opens into stomach present in abdominal cavity. Oesophagus anteriorly opens into pharynx through gullet and posteriorly into stomach through cardiac orifice.
  • Histology : Serosa is absent but outermost layer of connective tissue is called as tunica adventitia. Muscular layer are stratified voluntary in anterior region and unstriated involuntary in posterior part. The epithelial lining is made up of non-keratinized stratified squamous epithelial Goblet cells are present.
  • Function : Conduction of

(e)  Stomach


  • Structure : Single oval, elongated, unilobed present within abdominal cavity below It consists of three parts as



cardiac/fundic (anterior), corpus/body (middle, chief part) and pyloric (posterior part) in human, whereas in rabbit stomach is bilobed and consists of three parts as cardiac (Anterior) fundic (middle), chief part and pylorus (posterior). Two types of valves are present in the stomach viz. Cardiac sphincter valve between oesophagus and stomach and pyloric sphincter valve between stomach and duodenum.













  • Histology : Outermost layer is Muscular layer is three –

Fig. – Human stomach


layered with outer longitudinal, middle circular and inner oblique. Muscles are involuntary and unstriated. Epithelial


lining is made up of simple columnar epithelial cells and specialized cells present in the gastric glands. The nomenclature of gastric glands is according to the parts of the stomach. The various type of gastric glands and the cells present in them are as follows –

Anterior part : Cardiac gastric glands in rabbit and human cells present are mucous neck cells secreting mucous.

Middle part : Fundic gastric glands in rabbit and corpus in human has at least four distinct types of cells –

  • Peptic or zymogenic or chief or central cells : Secretes two digestive proenzymes pepsinogen and prorenin.


















  • Oxyntic or parietal cells : Secretes HCl and castle’s intrinsic factor required for the absorption of vitamin B12. Hyperacidity is a abnormally high a degree of acidity due to the secretion of large quantity of HCl e. gastric juice.
  • Mucous neck cells : Secretes alkaline
  • Argentaffin cells or Kultchitsky or enterochromaffin cells : Responsible for the secretion of vasoconstrictor







Fig. – L.S. Gastric gland






Posterior part : Pyloric gastric glands in rabbit and human-cells are mucous neck cells secreting mucous and some cells, called “gastrin” or “G” cells, secrete a hormone, named gastrin, which increases the motility of gastric wall and stimulates gastric glands for active secretion.

(3)  Functions

  • Storage of
  • Trituration or churning of food to mix with gastric juice.
  • Functions of gastric juice (discussed along with gastric juice).


  • Stomach of ruminants (cud- chewing mammals) : The stomach of cattles have four parts, as rumen (paunch), reticulum(honeycomb), omasum (psalterium) and abomasum (rennet). Some authors believe that first three chambers are parts of the oesophagus, the fourth chamber is the real stomach secretes HCl and The

embryological studies have proved that all the
















































chambers are parts of the real stomach.

Fig. – The compound stomach of a ruminant


The cattles rumen stores the quickly fed food. So cud chewing animals are called ruminants. e.g. cow, buffaloes, goat etc. Rumen is the largest part of stomach. Primitive digestion and bacterial action takes place in rumen. Which later on moves again to buccal cavity where it is properly chewed, then this food passes into reticulum to omasum which concentrates the food by

absorbing water and bicarbonates. Finally, the food reaches in the fourth chamber, abomasum. First three chamber are lined by cornified epithelium but fourth chamber abomosum is lined glandular epithelium and gastric glands, so it is true

stomach. Camel and deer lack omasum. Reticulum is the

smallest part and its cells are provided with water pockets for the storage of metabolic water.

In the  rumen,  food  undergoes  mechanical  and


chemical breakdown. Mechanical breakdown results from thorough churning brought about by muscular contractions and aided by cornified surface of villi. Chemical breakdown


Fig. – Arrow shows course of food


is caused by symbiotic microorganisms (bacteria and ciliates) that release enzymes, cellulase, which act on cellulose and simplify it to short-chain fatty acids, such as acetic acid, butyric acid, propionic acid. This is called microbial digestion. The fatty acids are neutralized by sodium bicarbonate of saliva and are absorbed. These two processes reduce the hard plant food to a pulp.





Important Tips

  • Lumen is the hollow space present in the middle of alimentary canal and is the site where process of digestion takes place
  • Stomach of frog is unilobed with two parts as anterior cardiac (various type of cells present in it secretes mucous, pepsinogen enzyme and HCl) and posterior pyloric (cells present secretes mucous). Frogs stomach has only pyloric sphincter valve present between stomach and
  • During hunger the folds of stomach deepen are called ‘rugae’.
  • The length of human alimentary canal is approximately 9–10
  • The length of the alimentary canal depends on the basis of feeding i.e. more complex the food (Herbivorous condition) more the length of alimentary canal, hence smallest alimentary canal is of carnivores and medium sized in omnivores.
  • Greenish faecal matter passed by infant in first two days of birth due to sterilized intestine is called meconium.
  • National institute of nutrition in Hyderabad.
  • Gastritis – Inflammation of stomach due to excessive intake of
  • Gastric ulcer (inflammation of mucosa of stomach) and duodenal ulcer is due to excess of acidic gastric
  • Amount of rennin decreases with age, then the curdling of milk is done by pepsin and
  • The policeman to the abdomen is omentum.
  • Removal of stomach causes dumpong syndrome.
  • The inner surface of small intestine is raised into longitudinal and circular fold called valvulae.
  • Chief cells of the gastric glands secreting zymogen, have well-developed rough
  • Argentaffin cells occur both in stomach and
  • Splanchnology is the study of the
  • Achalasia cardia – condition is characterised by failure of cardiac sphincter to relax completely on swallowing causing food accumulation in oesophagus and proximal oesophagus
  • Chyme is the acidic food which passes from stomach to
  • Stomach is the site for digestion of Size of stomach depend on the basis of proteineous diet, in carnivorous animal stomach large than herbivorous animal.
  • Oesophagus does not secrete any
  • Stomach absent in labeo, lamprey and hag
  • Hunger pangs Stomach churns every 20 second, when an empty stomach churns, hunger pangs are
  • Liver is well developed in carnivorous


(f)  Small intestine

  • Structure : Endodermal, longest part of alimentary present in the abdominal cavity, supported by a peritoneal membrane called Wall of jejunum and ileum has circular or spiral internal fold called fold of kerckring or valvulae conniventes. Also numerous finger like projection called villi project from the wall of lumen, increasing internal surface are about eight time. The distal end of ileum is leads into the large intestine by ileo- caecal valve in man but in rabbit sacculus rotundus and ileo-coecal valve both are present.
  • Parts : It is approximately 6 metres in human. It is divisible into three parts. In man small intestine divided into three parts –


Duodenum (Proximal part) Jejunum (Middle part) Ileum (Posterior part)
2.5 cm. Long

Forming U-shaped loop before leading to jejunum pancreas lies in the loop.

About 2.4 m long and about 4 cm. wide. Wall is thicker and more vascular.

Villi thicker and tongue-like. Plicae best developed.

Peyer’s patches are lacking.

About 3.6 m long and about 3.5 cm. wide. Wall is thinner and less vascular.

Villi thinner and finger-like. Plicae less developed.

Peyer’s patches are present.












































Fig. – Intestinal glands







Fig. – T.S. of duodenum showing intestinal


  • Histology : Serosa is the outer most Muscular layer is generalized with involuntary, unstriated muscles. The cells present in the epithelial lining are simple columnar epithelial cells, which are brush- bordered i.e. provided with villi and microvilli to increase the surface area. The folds present are longitudinal and are called folds of kerckring or valvulae canniventes. Goblet cells secrete mucous. Payer’s patches are the oval, rounded masses of lymphatic tissue present in between lamina propria and epithelial lining. They produce lymphocytes. Brunner’s glands or Duodenal glands are the multicellular mucous glands present in the submucosa of duodenum only. They secrete mucous. In addition there are also found granular arogyrophil cell.

(4)  Glands of small intestine


Brunner’s glands Payer’s patches Crypts of Leiberkuhn
Found in duodenum only. These are lymph nodules. Known as intestinal gland.
Mucus secreating gland as so known as mucus gland. They produce lymphocytes. Lymphocytes are phagocyte in nature which destroy harmful bacteria. Found in duodenum and ilium only.

Secrete succus entericus i.e. intestinal juice. Formed by folding of lamina propia.

Each gland has three types of cells : (i) Undifferentiated epithelial cell (ii) Zymogenic cell (paneth cell) and (iii) Argentaffin (Enterochromaffin cell).

  • Function : Digestion and absorption of
  • Large intestine : The name large intestine is due to large
    • Structure : Endodermal, approximately 5-1.75 metre long.
    • Parts : They are following –
      • Caecum : Spirally coiled 10-15 cm long in human and 45 cm long in Its posterior end is present as a blind sac in abdominal cavity called vermiform appendix. Vermiform appendix is vestigeal but contains lymphatic tissue. Caecum in human is concerned with passage of food whereas in rabbit it is concerned with cellulose digestion and conduction of food. Vompyrella bacteria helps cellulose digestion. Vermiform appendix produce antibody. It is functional in ruminents and vestigeal in man. If food may collect and decay in it or intestinal worms may settle in it and causes inflammation or appendicitis in man, in such case its removed by operation known as appendictomy.






  • Colon : Single endodermal approximately 1.3 m long in human distinguished into four limbs as ascending, transverse, descending and pelvic or sigmoid Colon posses two specialized structures as Taeniae (present in the middle of colon) and Haustra, (dilated sac-like or pockets like structures surrounding taeniae).

Serosa is the outer most layer. The serious layer (visceral peritoneum) forms small pendulous projections, the

appendices epiploicae filled with adipose tissue. Muscular layer is two layered contain involuntary unstriated

muscles. The innermost lining is made up of columnar epithelial cells. Goblet cells and absorptive cells are also present. Cells are without villi and microvilli i.e. not brush–bordered. Colon is concerned with absorption of water (80-85%), salts, vitamins etc. hence concerned with faeces formation. Colon bacteria also synthesized vit. B and K.

Differences between small and large intestines

Small intestine Large intestine
Longer (about 6 m.) but narrower than large intestine. Shorter (about 1.5 m.) but wider than small intestine.
Differentiated into duodenum, jejunum and ileum. Differentiated into caecum, appendix, colon and rectum.
Mucous membrane has plicae circulares and villi. Mucous membrane is mostly smooth (without plicae and villi).

Rectum has longitudinal folds.

Lacks taeniae coli, haustra and epiploic appendages. Has taeniae coli, haustra and appendices epiploicae.
Peyer’s patches are present in the ileum. Peyer’s patches not formed, lymphoid nodules beins scattered.
Completes digestion and absorbs digestion products. Also produces some hormones. Absorbs water, forms and eliminates faeces, produces vitamins B

and K by bacterial activity and excretes certain inorganic ions.

Mucosal irritation due to infection causes diarrhoea. Mucosal irritation due to infection causes dysentery.
  • Rectum : Single small dilated sac like in human whereas large beaded in rabbit. It is concerned with storage of faeces rectum has strong sphinctor muscle in its The sphinctor keeps the canal as well as anus, closed when not used for defecation.
  • Function : Absorption of water from undigested
  • Anal canal and anus : Anal canal connects rectum with anus and it is about 3 cm. long. Anus is the terminal inferior opening of alimentary canal, which is guarded by an internal involuntary sphincter and an external voluntary


(i)    Generalized histology of alimentary

canal : The alimentary canal consist of following




layers from outer to inner side:

  • Serosa : Outermost, mesodermal, single layered made up of squamous epithelial
  • Muscular layer : Mesodermal, consist of outer longitudinal and inner circular Muscles are











involuntary unstriated. In between the two layers there is a nerve network called the plexus of Auerbach.

  • Submucosa : Mesodermal, made up of connective tissue and contains major blood vessels, lymphatic vessels, nerve fibres Mucous

glands are also present in some parts of alimentary












canal. In this region nerve network, called plexus of Meissner.

Fig. – General structure of the wall of the mammalian gut and associated structures






  • Muscularis mucosa : Thin layer, made up of outer longitudinal muscles and inner circular The muscles are involuntary unstriated.
  • Mucosa : Inner most ectodermal in buccal cavity and anal canal whereas in the rest part of alimentary canal it is
  • Tunica propria (lamina-propria) : Outer, thin layer of connective tissue containing fine blood vessels, lymphatic vessels and nerve
  • Mucous membrane / epithelial lining : Ectodermal or endodermal, single layered, made up of columnar epithelial Goblet cells are also present in this layer. These cells are cup-shaped unicellular mucous glands secreting mucous. Epithelial lining is folded which are generally longitudinal and increases surface area.

Important Tips

  • Cellulose is digested by the enzyme cellulase synthesized by the microorganisms present in the


  • Cellulose

¾¾Cel¾lula¾se ¾b¾y ®

microbial fermentation

Acetic acid + Propionic acid + Butyric acid + Small chain fatty acid.


  • Sacculus rotundus is a dilated sac like structure present in rabbit at the junction of ileum, caecum and It contains ileo-caecal valve, which guides the direction of food from ileum to caecum. Sacculus rotundus is absent in human but ileo-caecal valve is present.
  • The hindgut of all vertebrates (except metatherian and eutherian mammals) includes cloaca and cloacal aperture, instead of anal canal and
  • Cloaca is divided into three parts

(i) Coprodaeum is a part of rectum, where faeces are stored.

  • Urodaeum a depression in the part of cloaca where urinary duct and urinary bladder
  • Proctodaeum terminal part of cloaca that is common opening for the excretion of urinary, genital and faecal matter and externally open by
  • Digestion of cellulose takes place in caecum of rabbit with the help of enzyme cellulase produced by symbiotic Cellulose digestion does not occur in human.
  • Peyer’s patches in the intestine are the site of production of B-lymphocyte.
  • In most of the vertebrate’s protein digestion ends in
  • The study of alimentary canal is called
  • Auerbach’s plexus is present in small
  • Digestion of cellulose is also found in termites (white ants). In which symbiotic flagellate Triconympha found in their intestine that secretes enzyme b-glucosidaes which hydrolyse the cellulose to sugars which are used by both
  • Bursa fabricus is also called cloacal thymus, is a lymphoid mass in the cloaca of It is site of differentiation of B-lymphocytes. So a part of immune system.


(ii) Digestive glands : The various types of digestive glands present in mammals are salivary glands, gastric glands, intestinal glands, pancreas and liver. The digestive glands secrete digestive juices. Parasympathetic nervous system increases the secretion of digestive juice whereas sympathetic nervous system decreases it.

  • Salivary glands : The three pairs of salivary glands present in humans are as follows –







  • Parotid : One-pair, largest salivary gland present below A stenson’s duct arises from each gland, opening between the teeth of upper jaw. Parotid glands secrete enzymes. Viral infection of parotid glands causes “Mumps”.





































Fig. – An acinus of salivary gland

Fig. – Location of salivary glands in man


  • Sub-mandibular / sub-maxillary : One-pair, present at the junction of upper and lower jaw in cheek A wharton’s duct arises from each gland and opens on lower jaw. These are seromucous glands.
  • Sub-lingual : One-pair, present in the floor of buccopharyngeal These are mucous glands 6-8 ducts, called ducts of rivinus or Bartholin’s duct arises from these glands and opens below tongue on the floor of buccopharyngeal cavity. The sub-lingual and sub-maxillary glands mostly secrete a glycoprotein called mucin (mucous secretion) while parotid glands secrete a watery fluid (serous secretion) which contains a digestive enzyme, the ptyalin or salivary amylase. Both these secretions together form the saliva. Infra orbital lie below the orbit and are absent in man.

Saliva / salivary juice : The secretion of salivary glands is called saliva or salivary juice. Some of the characteristics are as follows –

  • Amount : 1.5 litre/day
  • Chemical nature : Slightly
  • pH – 8
  • Control of secretion : Autonomic reflex (parasympathetic nervous system increases salivation while sympathetic nervous system inhibit )
  • Chemical composition : Water (98.2%), mucous (acts as lubricant), salts (NaCl, NaHCO3 ), enzymes (ptyalin, lysozyme) etc.

Functions : Salivary juice and its enzymes –

  • Makes the medium slightly acidic for the action of its
  • Help in taste detection, deglutition, speaking







  • Starch

Ptyalin/Diastase (Salivary amylase)

Maltose + Isomaltose + Limit dextrin.


  • Bacteria (living)

Important Tips

¾¾Lyso¾zym¾e ® Bacteria killed.




  • Gastric glands : There are approximately 35 million of gastric glands present in human stomach and grouped into three categories as already described along with The gastric gland secretes gastric juice.

Gastric juice

  • Amount : 2-3 liters/day.
  • Chemical nature : Highly acidic
  • pH ® 0 : 3.5 (due to presence of HCl)
  • Control of secretion : By gastric
  • Chemical composition : Water (99%), mucous, inorganic salts, castle’s intrinsic factor, HCl ( 5%, conc.) and enzymes prorennin and pepsinogen and gastric lipase.

Functions of gastric juice and its enzymes

  • Inactivates the action of
  • Makes the medium acidic for the action of gastric
  • HCl kills micro
  • HCl kills the living organism (prey ) if ingested.
  • Pepsinogen (inactive) ¾¾H¾Cl ®  Pepsin (active).
  • Prorenin (inactive) ¾¾H¾Cl ®  Rennin (active).


  • Pepsinogen (inactive)
  • Proteins + Peptones

¾¾Pep¾s¾in ®  Pepsin (active).

¾¾Pep¾s¾in ®  Polypeptides + Oligopeptides.



  • Casein (Soluble milk protein)

¾¾Chy¾mo¾sin/ ¾Ren¾in/ R¾enn¾et ®


Calcium paracaseinate (insoluble curd–like). Above


phenomenon is called “curdling of milk”.


  • Lipids

¾¾Ga¾stri¾c Li¾pas¾et ®

negligible inhuman stomach acts at pH 4-6

Triglycerides + Monoglycerides.


  • HCl is
  • It act as

Lactose intolerance : Among mammals, man alone takes milk even after becoming adult. In some humans, secretion of lactase decreases or ceases with age. This condition is called lactose intolerance. Lactose intolerant






persons fail to digest lactose of milk. In their large intestine, lactose fermented by bacteria, producing gases and acids. This causes flatulence (distension of stomach and intestine), intestinal cramps, abdominal pain and diarrhoea. These people can take yoghurt (yaourt)1 and or curd2 and cheese without any digestive problem. In yoghurt, lactose is fermented into lactic acid. In curd, lactose is left in the whey.

Important Tips


  • Intestinal glands : Intestinal glands in mammals is a collective name for crypts of Lieberkuhn (secretes alkaline enzymatic juice) and Brunner’s glands (secretes mucous). Intestinal glands secrete intestinal

(1)  Succus entericus (intestinal juice)

  • Amount : 5 – 2.0 l/day.
  • Chemical nature :
  • pH : 5-8.3
  • Control of secretion : Nervous and hormonal (Enterocrinin Duocrinin )
  • Chemical composition : Water (99%) mucous, inorganic salts, enzymes
  • Function : Intestinal juice and its
  • Inhibits the action of gastric
  • Makes the medium alkaline for the action of it’s


  • Starch

¾¾Am¾yla¾¾se ®  Maltose + Isomaltose + limit dextrin.


  • Maltose

¾¾Ma¾lta¾se ®

(a -glucosidase)

Glucose + Glucose.


  • Isomaltose

¾¾Iso¾ma¾lta¾se ®  Glucose + Glucose.


  • Lactose (milk sugar)

¾¾Lac¾ta¾se ®

(b -galactosidase)

Glucose +Galactose.


  • Sucrose (cane sugar)

¾¾Suc¾ras¾e /¾Inv¾erta¾¾se ®  Glucose + Fructose.

(b – fructosidase)


  • Polypeptides + Oligopeptides

¾¾Ery¾ps¾in ®

(Amino- peptidase)

Amino acids.


  • Trypsinogen (inactive)

¾¾Ent¾ero¾kin¾a¾se ®

Trypsin (active).


  • Lipids

¾¾Lip¾a¾se ®

Fatty acids + Glycerol + Monoglycerides.


  • Phospholipids

¾¾Pho¾sp¾hol¾ipa¾se ®

phosphorous + Fatty acids + Glycerol + Monoglycerides.







  • Organic phosphate

¾¾Pho¾sp¾hat¾a¾se ®  Free phosphate.


  • Nucleic acid

¾¾Pol¾ynu¾cle¾oti¾da¾se ®



  • Nucleosides

¾¾Nu¾cleo¾sid¾a¾se ®

Nitrogenous bases.


  • Pancreas : Single endodermal, flat, leaf-like yellowish, heterocrine (mixed) gland, present between the ascending and descending limb of duodenum and opens into duodenum through pancreatic



























Fig. – The gallbladder and pancreas and their systems of ducts. Both empty into the duodenum, often by a common orifice

(1)  Parts

  • Exocrine : It is the major part of pancrease. The exocrine tissue of the pancreas consists of rounded lobules (acini) that secrete an alkaline pancreatic The juice is carried by the pancreatic duct, also called duct of Wirsung, into the duodenum through the hepatopancreatic ampulla. An accessory pancreatic duct, also named duct of Santorini, may sometimes lead directly into the duodenum.
  • Endocrine : Minor part also called as islets of Langerhans scattered in the exocrine part. It consist of four various type of cells, as a(A) cells, b(B) cell and d(D) cells. a-cells secretes glucagon hormone, b-cells secretes insulin hormone and d cells secrets The secretion passes directly into blood.























































Fig. – An enlarged Islet of Langerhans

(2)  Pancreatic juice

  • Amount : 1-1.5 l/day
  • Chemical nature : alkaline
  • pH : 6
  • Control of secretion : Hormonal

Fig. – A part of a section pancreas


Secretin hormones stimulate the production of more alkaline pancreatic juice but low in enzyme content. Pancreozymin stimulates the production of enzyme rich pancreatic juice.

  • Chemical composition : Water (99%) enzymes and

(3)  Functions of pancreas and its enzymes

  • The islets of Langerhans secrete insulin and glucagon
  • The exocrine part of pancreas secretes pancreatic
  • Elastase : It act upon elastin


  • Trypsinogen

¾¾Ente¾rok¾inas¾e ¾of ®

Intestinal juice



  • Trypsinogen

¾¾Tryp¾s¾in ®




  • Chymotrypsinogen

¾¾Tryp¾s¾in ®




  • Polypeptides + peptones

¾¾T¾ryp¾sin ¾®

(Pancreatic protease)

Tripeptides + Dipeptides + Oligopeptides.


  • Starch

¾¾Am¾ylop¾s¾in ®

(Pancreatic amylase)

Maltose + Isomaltose + limit dextrin.


  • Emulsified Lipids Steapsin

(Pancreatic lipase)

Fatty acids + Glycerol + Monoglycerides.


  • Nucleic acid

¾¾Nuc¾lea¾se ®  Nucleotides + Nucleosides.







  • Nucleic acid

¾¾Nuc¾leas¾ida¾se ®  Purines + Pyrimidines.


  • Polypeptides

Important Tips

¾¾Chy¾mo¾tryp¾s¾in ®  Oligopeptides.













(e)  Liver


  • Structure : The liver is largest gland in the Its upper and anterior surfaces are smooth and curved to fit the under surface of the diaphragm; the posterior surface is irregular in outline.

It consists of three lobes in frog: right, left and median; five lobes in rabbit: left lateral, left central,

spigelian, right central and caudate; four lobes in






Fig. – Liver of man (ventral








man: right, left, quadrates and caudate lobe. These are surrounded by a thick capsule, mostly overlaid with reflected peritoneum. It is heavier in males than females. In males it generally weights 1.4 – 1.8 kg and in females 1.2 – 1.4 kg. It is divided into two main lobes : right and left lobes separated by the falciform ligament. The latter is a membrane that is continuous with the peritoneum. The right lobe of the liver is differentiated into right lobe proper, a

quadrate lobe and a caudate lobe in the inferior


























side. A pear-shaped sac, the gall bladder is attached


Fig. – Liver and pancreas and their






to the posterior surface of the liver by connective tissue. The right and left hepatic ducts join to form the common hepatic duct. The latter joins the cystic duct, which arises from the gall bladder. The cystic duct and common hepatic duct join to form bile duct, which passes downwards posteriorly to join the main pancreatic duct to form the hepatopancreatic ampulla (ampulla of Vater). The ampulla opens into the duodenum. The opening is guarded by the sphincter of Oddi. The sphincter of Boyden surrounds the opening of the bile duct before it is joined with the pancreatic duct. The basic structural and functional unit of the liver is the hepatic lobule.

The liver is encapsulated in rabbit and man by two sheaths-an outer membranous serous capsule consisting of visceral peritoneum and an inner Glisson’s capsule of a thin layer of dense connective tissue. In frog Glisson’s capsule is absent. Numerous thin and profusely branched septa-like trabeculae extend inwards from Glisson’s capsule, dividing each liver lobe into numerous minute and polyhedral units called hepatic lobules. Thus, the adjacent lobules are separated by interlobular Glisson’s capsules. Each hepatic lobule is about one millimetre in diametre. A slender intralobular branch of hepatic vein, called central vein or venule, forms the axis of each lobule.





































Fig. –Showing gall bladder, different ducts and hepatopancreatic ampulla

Fig. – Showing sphincter of boyden and sphincter of oddi




Each lobule is composed of plates of polyhedral, glycogen-rich cells, the hepatocytes, arranged radially around a central vein. Between the plates are radial blood sinusoids. At the periphery of the lobules, the branches of portal vein, hepatic artery, bile ducts, and lymphatics course together. A network of tubular spaces between the hepatocytes represents the bile canaliculi. At the periphery of the lobule the bile canaliculi empty into small hering’s canals walled by cuboidal epithelium. These canals lead into bile ducts walled by columnar epithelium. The sinusoids are lined by incomplete endothelium with scattered phagocytic Kupffer cells, that eat bacteria and foreign




































Fig. – Structure of liver






Gall bladder : The gall bladder is a slate-blue, pear-shaped sac connected with an supported from liver by a small omentum or ligament. Its distal part is called fundus, while the narrow part, continued as cystic duct, is called the neck.

  • Functions of liver : Liver, the largest gland of vertebrate body, is an essential organ, which performs many functions –
    • Secretion : It secretes bile which is a complex watery fluid containing bile salts (Na taurocholate and glycocholate), bile pigments (biliverdin and bilirubin), cholesterol, mucin, lecithin and fats etc. The bile aids in intestinal digestion as it breaks and emulsifies the fat, prevents putrefaction of food by checking the growth of bacteria, makes the chyme better suited for pancreatic digestion by neutralizing the acid in it, and helps in the absorption of fat from the
    • Excretion : In the liver, haemoglobin of the worn out erythrocytes breaks down to bile pigments bilirubin and biliverdin. The liver excretes these pigments as a major constituent of bile, a part of which carried to the kidney through general circulation for excretion through urine. The bile pigments are also converted in the bowel into stercobilin which colours the faeces but, apart from this, are waste products having no other


  • Glycogenesis : Excess quantities of carbohydrates (glucose) are converted to glycogen in the presence of insulin in the liver cells, and stored
  • Glycogenolysis : Glycogen is a reserve food material, which is changed into glucose and released into the blood at concentrations maintained constant by the In this way, blood–sugar level is maintained under diverse dietary conditions.
  • Gluconeogenesis : Under abnormal conditions, liver can convert proteins and fats into glucose by complex chemical reactions. Formation of this “new sugare. from non–carbohydrate sources, is called gluconeogenesis.




























  • Lipogenesis  :   If the level of

blood–glucose rises beyond normal even

Fig. – A part of a section of rabbit’s liver


after glycogenesis and catabolism, the excess glucose is converted into fat and stored in the liver. The process is termed lipogenesis.

  • Transamination and deamination : Amino acids resulting from protein digestion finally come into the liver from the intestine. They are partly released into the blood for distribution and protein synthesis, partly transaminated into other amino-acids and Any resulting keto-acids are converted into carbohydrates or fats and the free amino-groups appear as ammonia. This is excreted as such (e.g., aquatic animals) or after prior conversion to urea (e.g. amphibians, mammals) or uric acid (e.g., insects and birds).





  • Haemopoiesis : In the embryo, red blood cells are manufactured by the liver. In the adult, liver stores inorganic salts of iron, copper and vitamin B12 (anti–anaemic factor) and thus helps in the formation of red blood cells and
  • Store-house of blood : Liver functions as a store–house for blood and regulates blood–volume.
  • Blood clotting : Fibrinogen, prothrombin and certain other blood coagulation factors are formed in the liver which are instrumental in blood clotting. Heparin is an intravascular anticoagulant that is stored in the liver. It originates in mast cells, which are abundant in the liver, among other
  • Production of plasma proteins : The plasma proteins serum albumin and serum globulin are synthesized by the liver from the amino acids derived from the protein in the
  • Synthesis and storage of vitamins : Liver synthesizes vitamin A from the provitamins A (carotenoid pigments). Liver cells also store fat–soluble vitamins A, D, K and Besides, it is the principal storage organ for vitamin B12.
  • Detoxification : It is the process by which toxic substances are rapidly made excretable through different biochemical changes. The liver is the site of detoxification of different toxic substances either produced in the body or taken along with food. This is done by the process of oxidation, hydrolysis, reduction and conjugation. Many drugs like phenylbutazone pethidine, chloromycetin are also made excretable by the liver enzymes.
  • Alcohol metabolism : Liver is the main site of alcohol metabolism. By various enzymes in the liver, alcohol is first catabolised to acetaldehyde, which is converted into acetyl The latter may be oxidised to CO2 and H2O or converted to other biochemical compounds including fatty acids through TCA cycle. The direct effect of alcohol may be alcoholic fatty liver, which results from increased fatty acid synthesis.
  • Desaturation of fats : Fats is stored in the body in a saturated form (e., they cannot take any more hydrogen into their composition). Before the saturated fats can be used by the tissues of the body, they are conveyed to the liver, which converts them into unsaturated form (by the removal of hydrogen). The unsaturated fats are then used by the tissues to provide energy.
  • Heat production : A large number of chemical processes are carried out by the liver, that involve the production of a great deal of It is the main heat producing organ of the body.
  • Phagocytosis : Kupffer cells in the liver sinusoids phagocytose and remove bacteria, worn-out blood elements and foreign
  • Lymph formation : Liver is an important site of lymph

(iii)  Bile/chole :

  • Amount : 6-1 litre/ day (2) Source : Secreted by hepatic cells

(3) Storage site : Gall bladder                          (4) Colour : Greenish-blue

(5) Chemical nature : Alkaline                          (6) pH : 7.7-8.0

  • Control of secretion-Hormonal, hormone concerned is cholecystokinin (cck) or pancreozymin (pz).





  • Composition –
    • Water : 90% in (Gall bile), and 98% in hepatic
    • Mineral salts and NaHCO3(increases alkalinity)
    • Mucous
    • Bile salts : Sodium taurocholate and sodium glycocholate causes fat emulsification
    • Bile pigments : Bilirubin and biliverdin
    • Cholesterol
    • Lecithin
    • Bile pigment bilirubin (yellow colour) and biliverdin green (green colour)
    • The quantity of bilirubin is more in carnivorous animals but in quantity of biliverdin is more in herbivorous animal.
  • Functions of bile
    • Emulsification of
    • Helps in absorption of fat-soluble
    • Increases alkalinity to make the medium suitable for enzymatic
    • Elimination of heavy metals such as Cu, Hg, Zn
    • Elimination of excess of bile
    • Stercobilin and urobilin is formed by bilirubin and biliverdin is responsible for colouration of

Important Tips






 Physiology of digestion.

The process of digestion involves following steps –


  • Ingestion : It is the intake of food most of the animals capture the prey/food with the help of mouth or Such as frog, rabbit, cattle etc. Some are filter–feeders such as paramecium, pila etc. In human food is ingested with the help of hands.
  • Mastication : The process occurs in the buccopharyngeal cavity of mammals with the help of teeth. During this process food is broken down into small pieces, which increases its surface In frog teeth are not meant for mastication but prevents the escape of prey from mouth.
  • Degglutition / swallowing : The passage of food from buccopharyngeal cavity to oesophagus/stomach. In mammals bolus of the masticated food is formed in buccopharyngeal cavity which easily slides into It is a voluntary reflex mechanism. Peristalsis is alternative contraction and relaxation of circular and longitudinal muscles produces the wave of contraction due to which the food passes from front to backward direction in the lumen of alimentary canal. The phenomenon is called as peristalsis. Beside alimentary canal, it is also found in vas deference, ureter etc.

Peristalsis in stomach is called trituration or pendular movement, in small intestine segmentation pendular movement. Whereas in large intestine (colon) it is called as haustration or segmentation movements. Peristalsis is maximum in oesophagus and minimum in rectum.

Antiperistalsis is the peristaltic wave occurs in the reverse direction. It occurs in alimentary canal and results in vomiting. The phenomenon is called as “Regurgitation”. The food, which passes out through mouth in vomiting, is





chiefly of stomach and sometimes from the anterior part of duodenum. Vomiting may also be due to blockage of gut or amalstasis. Vomiting centre is present in medulla oblongata.

  • Digestion : The process by which complex food is converted into simple food with the help of digestive The process of digestion in mammals starts in buccopharyngeal cavity and is found in stomach and small intestine, whereas in frog the process starts in stomach and continues in small intestine.
  • Digestion in buccopharyngeal cavity : In buccopharyngeal cavity of mammals only starch is digested which is 5% of total food or 20-30% of
  • Digestion in stomach : Chiefly proteins is digested in


  • Digestion in small intestine : All three component carbohydrates, proteins and fats digested in small intestine with the help of enzymes secreted by pancreas and intestinal About 50% of starch is digested by pancreatic amylase and 10-20% by intestinal amylase. Only 60% of lipids are digested in the small intestine major part of proteins is digested in the stomach. The end product of digestion is as follows –

Summary of chemical digestion of food

Chemical digestion of protein Chemical digestion of carbohydrates Chemical digestion of fats Chemical digestion of nucleic acid
Protein Food


Pepsin (gastric juice)



Proteoses and Peptones

Trypsin and Chymotrypsin (pancreatic juice)


Tri and Dipeptides

Peptidases (intestinal juice)


Amino acids




Ptyalin (saliva)


Amylase (pancreatic juice)





Maltase, Lactase Sucrase (intestinal juice)


Monosaccharides (glucose, fructose, galactose)



Bile salts (bile)


Emulsified Fats Lipase (pancreatic and intestinal juice)



Fatty acids and glycerol

Nucleid acid

(DNA and RNA)

Pancreatic nucleases (DNAase & RNAase)



Intestinal Nucleotidases and Nucleosidases



Nitrogen bases Pentose sugars and inorganic phosphate

  • Absorption : Ingestion and digestion are the first two phases of the physiological processes occuring in the alimentary The third phase is that of absorption by which the digested nutrients are absorb through the wall of gut into blood.






  • Absorption from the mouth : Normally, there is no absorption from the mouth, but a few drugs may be absorbed into the blood through the mucous membrane, if allowed to dissolve under the tongue, g., isoprenaline, glyceryl trinitrate.
  • Absorption from the stomach : In the stomach, absorption takes place to a limited degree. The only substances normally absorbed from the stomach are some water, glucose and

considerable amounts of alcohol. These substances are absorbed through the walls of the stomach into the venous circulation. Although iron absorption takes place in the small intestine, it is dissolved out of foods most effectively in the stomach in the presence of HCl.

  • Absorption from the small intestine : The small intestine is the main absorptive organ. About 90% of the ingested foodstuffs is absorbed in the course of passage through the small intestine. The surface area of the intestine through which absorption can take place is vastly increased by the circular folds (plicae semilunares) of the mucous membrane and by the large number of villi. The intestinal wall appears very much like a Turkish Surface area of the intestine


is further increased by the microscopic folds, the microvilli, protruding out from the surface of the intestinal epithelial cells.

Fig. – Valvulae conniventes and villi in human intestine


There are two general pathways for the transport of materials absorbed by the intestine; the veins of the hepatic portal system which lead directly to the liver; and the lymphatic vessels of the intestinal area, which eventually lead to the blood by way of the lymphatic system and the thoracic duct.

  • Absorption of carbohydrates : The products of carbohydrate digestion is absorbed from the intestine into blood of the portal venous system in the form of monosaccharides, chiefly the hexoses (glucose, fructose, mannose and galactose). Two mechanisms are responsible for absorption of monosaccharides: active transport (against concentration gradient) and simple diffusion. Active transport takes place through carrier proteins and considerable amount of Sodium ions (Na+) play an important role in this carrier transport system. Hence it is called Na+ co-transport mechanism.
  • Absorption of amino acids and protein : It is probable that under normal circumstances the dietary proteins are almost completely digested to their constituent amino acids and that these end products of protein digestion are then actively transported from the intestine into the portal There are exist several different carrier systems for transporting different classes of amino acids. Some of these required Na+, just as in the case of carbohydrate transport. Surplus amino acids are also withdrawn from portal blood by liver cells and deaminated into ammonia and keto acids. The ammonia is converted to urea and released into blood for excretion by kidneys, while the keto acids are converted to glucose or pyruvic acid and utilized for energy-production or for storage as glycogen and fat.
  • Absorption of fats : The dietary fat is digested, by the action of the pancreatic lipase present in the intestine, partially into glycerol and fatty acids and partially to split products such as monoacyl These products of fat digestion enter the mucosal cells of the small intestine in two forms.
  • Some of the liberated fatty acids and monoacyl glycerols aggregate to form water-soluble particles known as micelles. The structure of a micelles is similar to that of the lipid emulsion except that these are smaller in Formation of micelles helps absorption of free fatty acids and monoacyl glycerols from intestinal lumen into the epithelial cells by simple diffusion.







Fig. – Formation of micelle

  • With the aid of the bile salts many fatty acids and glycerol enter the epithelial cells of the intestinal mucosa. During their passage through the epithelial cells, they combine together resulting in the resynthesis of triacylglycerides.


Coenzyme A + Fatty acid

¾¾Thio¾kin¾a¾se ®Fatty acyl Co ~ A


ATP      AMP + PPi

Monoglyceride ¾¾® Phosphatidic acid ¾¾®



Fatty acid ¾¾®

¯ Triglyceride (neutral fat)


The resynthesized fat then passes into the lacteals (lymph vessels) of the intestinal villi, primarily in the form of small lipid droplets about 0.5 mm in diameter, known as chylomicrons. These small droplets contain about 90% triglyceride and small amounts of phospholipid, cholesterol, free fatty acids and protein. By the lacteals, the fat is carried to the cisterna chyli (meaning ‘the receiver of the chyle’) and then by the thoracic (lymph) duct to the left branchiocephalic vein, where it enters the blood. The lymph reaching the thoracic duct from the intestines contains an excess of fat giving it a milky appearance. It is called chyle. In this way, fatty acids and glycerol are eventually brought into the blood stream and so, by a circuitous route, to the liver. In the liver, they are reorganized and recombined to form human fat.







AND GLYCEROL                                                 AMINO












Fig. – T.S. Intestine showing absorption of food


  • Absorption of vitamins : Water-soluble vitamins like members of B complex (except B12) and vitamin C readily diffuse across the walls of the intestine into the To move vitamin B12 across the wall of the ileum, a special system is required. In the stomach, the vitamin combines with a special protein secreted by the gastric glands, known as the castle’s intrinsic factor. During the absorption process in the ileum, vitamin B12 is released from the intrinsic factor and enters the blood. The fat-soluble vitamins A, D, E and K are dissolved in micelles,





which enter the mucosal cells of the intestine, by simple diffusion. The absorption of these fat-soluble vitamins is markedly decreased in the absence of bile.

  • Absorption in large intestine : Major part of the water is absorbed in the It helps in maintaining the body water level. Some amount of mineral salts and vitamins are also absorbed. The symbiotic bacteria (E. coli) present in the large intestine, converts the inactive vitamins into active forms (i.e., they synthesizes vitamins (vitamin B complex and vitamin K) which are absorbed. It has been also found that some amount of amino acids is also absorbed in large intestine produced due to digestion, with the help of symbiotic bacteria. The epithelial cells of large intestine secrete no digestive enzyme.
  • Assimilation : Conversion of absorbed food into active cytoplasm within cell is called as
  • Faeces formation : The phenomenon occurs in colon due to absorption of water, salts, minerals and The peristalsis in colon also helps in faeces formation.

Differences between diffusion and active transport


Diffusion Active transport
It is a physical process. It is a vital process.
It moves small nutrient molecules across the cell membranes only down the concentration gradient. It moves small nutrient molecules across the cell membranes independent of concentration gradient (both down and against).
It does not use carrier protein molecules in moving materials. It uses carrier protein molecules in moving materials.
It does not utilize energy. It consumes energy derived by hydrolysis of ATP.
It is a slow process. It is a rapid process.
No material can be fully absorbed by diffusion. Materials can be fully absorbed from the intestine.
  • Egestion / defaecation : At fairly long intervals, a wave of strong peristalsis sweeps along the transverse colon forcing its contents into the descending and pelvic colons. This is known as mass movement, which is often precipitated by the entry of food into the stomach and is known as the gastro-colic When a mass movement force the contents of the pelvic colon into the rectum, the nerve endings in the walls of the rectum are stimulated the act of defaecation, while reflex in the infant, and adult is under the control of the will.

(a)   Actions during defaecation

  • The sphincter muscle of the anus


  • The muscular walls of the rectum
  • The muscles of the floor of the pelvis
  • The pressure within the abdomen is
  • By holding the breath and contracting the

Fig. – Transformation of absorbed





  • By contracting the muscles of the abdominal wall.

The defecation is carried out in response to the desire in children and adults, to empty the bowel production by distension of the rectum with faeces. Biliverdin and bilirubin are reduced to urobilinogen in the large intestine. Urobilinogen in the large intestine is converted to stercobilin. The odour of the stool is due to aromatic substances like indole and skatole. Indole and skatole result from the action of bacteria on amino acid tryptophan.

  • Constituent of faeces : The faeces, consist of a semi-solid, paste-like mass coloured brown by stercobilin, a pigment derived from the bilirubin and biliverdin of the
    • Water (65-70% of the total bulk) (2) Undecomposed cellulose

(3) Protein residue (skatole, histidine, indole and tryptophan)          (4) Dead and live micro-organisms

(5) Epithelial cells from the walls of the tract                              (6) Some fatty acids

(7) Mucous-secreted by the mucosa lining of the large intestine.

Pseudo-rumination or coprophagy : Animals swallows night faeces and recycle it through the gut to complete the digestion of cellulose and, making full use of their food. This habbit is called coprophagy. Example – Rabbit.

Name of gland Name of digestive juice & optimum pH Name of enzyme Site of action Substrates Products
Salivary glands Saliva (6.8) Ptyalin / Salivary amylase Mouth Starch, dextrins, glycogen Dextrins, maltose, isomaltose and limit dextrin.
Gastric glands Gastric Juice (1-3) Pepsin Stomach Proteins, casein (Milk) Peptones, paracasein (curd). Proteases
Rennin Stomach Casein Paracasein
Gastric lipase Stomach Fats Fatty acid and Glycerol.
Bile juice Liver No enzymes Duodenum Fat Makes the food alkaline, emulsifies fat and kills the harmful bacteria.
Liver Bile ( 7.7 – 8.0) No enzyme but useful digestive juice, provides alkaline medium, stops the action of HCl. Emulsifies fats and kills – harmful bacteria.
Pancreas Pancreatic Juice (7.3 – 8.6) Amylase/Diast-ase Small intestine Starch,

dextrins, glycogen.

‘Limits’ dextrins, maltose, isomaltose.
Trypsin Small intestine Proteins,

Chymotry-psinogen (inactive) procarboxy pept- idases (inactive) Fibrinogen (blood) Casein (milk)

Peptides, Chymotrypsin (active) carboxy pepti-dases (active) Elastase (active), Fibrin (clot) Para-casein (curd)
Chymotrypsin Small intestine Peptones Peptides
Carboxypeptidases Small intestine Peptides Smaller peptides and Amino acids.


Summary of physiology of digestion Major gastrointestinal enzyme in mammals





    Lipase / Steapsin Small intestine Triglycerides Mono-glycerides, fatty acids
DNA ase Small intestine DNA Deoxyribonucleotides
RNA ase Small intestine RNA Ribonucleotides
Intestinal glands Intestinal Juice (7.6–8.3) Enteropeptidase (enterokinase) Small Intestine Trypsinogen (inactive) Trypsin (active)
Aminopeptidase Small Intestine Peptides Smaller peptides and amino acid
Dipeptidases Small Intestine Dipeptides ‘Limit’ dextrins Amino acids
Isomaltase Small Intestine Isomaltose Glucose
Maltase Small Intestine Maltose Glucose
Sucrase/Invertase Small Intestine Sucrose Glucose, fructose
Lactase Small Intestine Lactose Glucose, galactose
Lipase Small Intestine Triglycerides Monoglycerides, fatty acids
Nucleotidase Small Intestine Nucleotides Nucleosides, inorganic phosphate
Nucleoside Phosphorylases Small Intestine Nucleosides phosphate Purine, pyrimidine, pentose, phosphate


  • Hormonal control of digestion : Activities of digestive tract are coordinated by nervous and endocrine Sight and smell of food stimulates nervous system which induces the salivary glands to produce large quantity of saliva, stomach to release its hormone gastrin and intestine to produce intestinal hormones. Other hormones are produced in sequential order. All of them are polypeptide hormones.


Gastrointestinal hormones in mammals


Hormone Source Stimulus for


Target organ Action
Gastrin Mucosa stomach of pyloric Distension of stomach on food entry Stomach Stimulates secretion of gastric juice.

Constricts cardiac sphincter.

Enterogastrone Duodenal epithelium Chyme         entry duodenum into Stomach Slows gastric contractions emptying.

Stops secretion of gastric juice.

to delay its
Secretin Duodenal epithelium Acidic chyme entry duodenum into Pancreas


Liver Stomach

Release of sodium bicarbonate in pancreatic juice.

Steps up secretion of bile.

Inhibits secretion of gastrin.

Cholecystokinin (Pancreozymin) Duodenal epithelium Presence of fats in duodenum Pancreas Gall Bladder Release of enzymes in pancreatic juice.

Release of bile from gall bladder.

Villikinin Intestinal epithelium Food in small intestine Intestine Accelerates movements of villi.
Duocrinin Intestinal epithelium (Duodenal mucosa) Acidic chyme in intestine Intestine (Brunner’s gland) Release of viscous mucous from Brunner’s glands.
Enterocrinin Intestinal epithelium

(Duodenal mucosa)

Acidic chyme in intestine Intestine (crypts of Lieberkuhn’s) Release of enzymes from Lieberkuhn’s crypts.





Important Tips

  • World food day (W.F.D) is 16th
  • Iodine deficiency disorder day (I.D.D.D) : is 21st
  • White revolution – Increased milk
  • Blue revolution – Increased fish
  • Yellow revolution – Increased oil
  • High cholesterol patients are avoided to use groundnut oils, margarine and vegetable
  • The foul & flatus odour of the faeces is due to presence of gases such as CH4, NH3, H2S, CO2 and presence of indole, skatole and mercaptones amines formed due to decarboxylation of tryptophan amino acid.
  • Digestion of fat is slowest and never
  • Main aim of nucleic acid digestion is to release phosphate
  • Villus is the unit of absorption of
  • Fructose and mannose are absorbed by facilitated diffusion.
  • Role of bile salts is to form water soluble mixed micelles is called hydrotrophic
  • Chyle is the alkaline food, which passes from small intestine to
  • It takes about 2-6 hours after a meal for the stomach to
  • Aminopeptidase, a digestive enzyme produces smaller
  • In most of the vertebrates protein digestion ends in
  • The enzymes that converts glucose to glucose 6-phosphate is
  • Amylopsin act on
  • Most of the fat digestion occurs in small
  • Lipase hydrolyse ester
  • Protein digestion is necessary because it cannot be absorbed as
  • Carbohydrate are digested in
  • Amylase broken 1,4 glycosidic bonds of
  • Loose bond of enzymes between proteinous and prosthetic groups can be separated by the process of
  • Enzyme, vitamins and hormones are biological chemicals which aid in the regulating
  • Enzymes accelerate the rate of chemical
  • Human insulin is known as Humulin.
  • Stimulation of acid secretion of stomach is due to gastrin, histamine and vagal
  • The end product of carbohydrate metabolism is CO2 and H2
  • Mammals also get water from the oxidation of



The substance used for nutrition are called nutrients. Nutreology is the study of food and their use in diet and therapy.





(i)  Types of nutrition

  • Autotrophic / Holophytic : The individuals, which synthesizes their own food. It can be grouped into two following categories –
    • Photoautotrophs : The individual, which synthesizes their own food from CO2 and H2O in presence of These individuals have a specialized pigment chlorophyll in their cells. Examples – Green plants, euglena, green sulphur bacteria, chlorobium.
    • Chemoautotrophs : The individuals which synthesizes their food with the help of The energy consumed in synthesis of nutrients is obtained from oxidation of hydrogen gas, ammonia, methane, hydrogen sulphide, nitrites etc. Examples – Sulphur bacteria, nitrite bacteria, nitrate bacteria, nitrosomonas, nitrifying bacteria– nitrosomonas, nitrobacter etc.
  • Heterotrophic : The animals derive organic food materials by consuming bodies or products of other living or dead plants or Heterotrophs are of following three types on the basis of their mode of feeding.
    • Holotrophic or Holozoic : These individuals ingest mostly solid Example – Animals.
    • Saprotrophic or Saprobiotic : They feed on dead organic They absorb food through their body surface, organic fluids formed due to putrefaction of dead organism. These are called saprozoic if the putrefying organism is an animal and saprophytic, if the later is a plant. Saprobionts usually themselves pour out certain enzymes which hydrolyses the complex molecules of putrefied food and help in absorption. Saprozoic nutrition involves absorption of food by osmosis, i.e., through general body surface. This method of food-getting is referred to as osmotrophy and animals are called osmotrophs. Example – Bacteria, fungi, some protozoans etc.
    • Parasitic : These individuals derive their food from the body of their These may live inside or upon the bodies of their hosts, or may only periodically visit them for feeding.
  • Myxotrophic nutrition : They carry out autotrophic as well as heterotrophic nutrition. Example –
  • Modes of animal nutrition : On the basis of food, holozoic or holotrophic or ingestive nutritionally animals are classified into following –
  • Herbivorous : The animal which exclusively feeds on Their length of alimentary canal is more as compared to others. Examples – Tadpole larva of frog, rabbit, cow, horse, sheep etc.
  • Carnivorous : The animal which kills and feeds on other The length of their alimentary canal is minimum. Examples – Tiger, lion etc.
  • Omnivorous : The animal which can take both plant and animal product as food. They have maximum type of digestive Example – Human.
  • Insectivorous : The animal which feeds on Example – Frog.
  • Sanguivorous : The animal which feeds on blood of other Examples – Leech, body louse.
  • Carrion Eaters (scavengers) : They feeds on dead animals also termed as scavengers. Examples – Hyaena, neltura, kites





  • Cannibalus : Organisms which feeds on its own species. Examples – Cockroaches, some fishes, frog, snakes
  • Detritus : Animals feed chiefly upon organic matters present in the Examples – Earthworm.
  • Coprophagus or pseudorumination or refection : Animals which feeds on their own Example
  • Larvivorous : Feeds on Example – Gambusia (mosquito fish).
  • Frugivorous : Feeding on Example – Parrot.

(iii)  Feeding mechanism

  • Feeding mechanism in liquid feeders (fluid feeders) are as follows –
    • Diffusion : Many parasitic organisms (protozoans, tapeworm) absorb the dissolved organic food through general body
    • Pinocytosis (cell drinking) : Ingestion of liquid food by invagination through surface of body. Pinocytosis channels are formed at body surface to enclose the fluid food from surrounding medium. Lower ends of channels are pinched off as pinocytic vesicle or
    • Blood sucking : Their mouthparts are modified for sucking Examples – Vampire bat, mosquito etc.
  • Feeding mechanism in microphagus animals (filter feeders) : The food of such animals (paramecium, sponges, corals, bivalves, tadpole ) is suspended in water fluid and they have filtering devices (clusters of pseudopodia, cilia, flagella, sheets of mucous etc.) or feeding on small microscopic animals like – Amoeba, paramacium etc.

 Nutritional requirements.

  • Food : All living organism needs food, animal are unable to synthesize their own food hence they obtain it from outside Animals require food for three main purposes, such as food as a fuel which provides energy and material for body maintenance, food for movement of body includes muscles contraction etc., food for growth as well as for the synthesis of body substances.
  • Components of food : These are following types –


(a) Carbohydrates (b) Lipids and fats (c) Proteins (d) Nucleic acid
(e) Water (f) Vitamins (g) Minerals      
  • Carbohydrates : They are made up of C : H : O, having H and O in the ratio of 2 : 1 and the general formula is CnH They are the chief source of The source of carbohydrates in our food is cereals and pulses.
    • Classification of carbohydrates : Carbohydrates are grouped into three categories –
      • Monosaccharides : Simplest They are of following types –
    • Trioses : (C 3 H 6O3 ); Example – Glyceraldehyde,
    • Tetroses : (C4 H8 O4 ) ; Example – Erythrose.
    • Pentoses : (C5 H10 O5 ); Example – Xylose, ribose, arabinose.





  • Hexoses : (C6 H12O6 ) ; Example – Glucose, fructose, galactose.
  • Heptoses : (C 7 H14O7 ); Example –
    • Oligosaccharides : They contain 2 – 9 molecules of They are of following types –
  • Disaccharides : Examples – Maltose (malt sugar), sucrose (cane sugar), lactose (milk sugar),
  • Trisaccharides : Example – Raffinose, mannotriose
  • Tetrasaccharides : Example – Stachyose, scordose
  • Pentasaccharides : Example –
    • Polysaccharides : Two types –
  • Homosaccharides : When polysaccharides are made up of single kind of monosaccharide. Examples – Starch, glycogen, cellulose, agar-agar and dextrin
  • Heterosaccharides : When polysaccharides are made up of two or more kind of monosaccharides or their Examples – Mucopolysaccharides, chitin, peptidoglycan and heparin etc.

(2)  Specific features

  • Storage amount : 900 gm
  • Storage site : Chiefly liver and muscles.
  • Daily requirement : 500 gm approx.
  • Source : Chiefly cereals (rice, wheat, maize), pulses, potato, fruits, sugarcane, milk, honey, sugar
  • Caloric value : 4.1 k cal./gm
  • Physiological value : 0 k cal./gm
  • Carbohydrates may have an aldehyde (aldoses) or ketone (ketoses)
  • Simple carbohydrates having free aldose or ketose group are called reducing sugars.
  • Reducing sugars can reduces cupric ion to cuprous state (Fehling’s or Benedict’s solution)
  • Fructose (levulose) is fruit sugar while glucose (dextrose) is grape sugar as well as blood
  • Two monosaccharides are linked by means of ‘glycosidic bond’ (C–O–C) in formation of a This is a dehydration or condensation reaction.
  • Comparing to the milk of cow, buffalo and goat, lactose is highest in human milk.
  • Chitin is a polysaccharide found in the exoskeleton of arthropods. Its basic unit is not glucose but N-


  • Our food mostly contains

(3)  Functions of carbohydrates :

  • As respiratory fuels : Carbohydrates, especially glucose, are the main respiratory fuels. About 60% of our total energy needs is provided by the breakdown of carbohydrates. Caloric fuel value of one gram of carbohydrates is 1 k cal of energy while physiological fuel value of one gram of carbohydrates is 4.0 k cal (17 kJ) of energy. To provide energy, the glucose undergoes biological oxidation in the mitochondria (power house) of the





cell to produce about 36 or 38 molecules of ATP. So the theoretical recovery of energy from one glucose molecule is 40%. Main reasons for the glucose being chief respiratory fuel are its presence in abundance and its easy oxidisability.

(ii)  Monosaccharides as structural components

  • Ribose (Pentose sugar) is component of RNA; coenzymes like NAD, FAD etc., and energy carriers like ATP, GTP
  • 2’-Deoxyribose (Pentose) is component of
  • Galactose is a structural component of medullary
    • As building blocks : Monosugars act as monomers for the formation of disaccharides and
    • Reserve foods : There are two main polysaccharides which act as reserve foods g. starch is a storage polysaccharide of plants and is stored as granules in amyloplasts. Glycogen (animal starch) is the principal reserve food of animals and is mainly stored in liver (about 500 gms.) and skeletal muscles. Liver glycogen is used to regulate blood sugar level by the process of glycogenolysis or glycogenesis as required while the muscle-glycogen provides energy for muscle contraction.
    • Excess of glucose may also be changed into fats (lipogenesis) and stored in liver, adipose tissue and
    • Glucose has antiketogenic role as it prevents the incomplete oxidation of fats and formation of ketonic bodies in the
    • Glucose spares the amino acids for protein
    • Sucrose is the major form in which sugar is transported in the plant Sucrose is storage sugar of sugarcane and sugar beet.

(ix)  Polysaccharides as structural components

  • Cellulose, hemicellulose are the main components of cell wall of plants.
  • Chitin is main component of cell wall of fungi and exoskeleton of
    • Anticoagulants : Heparin prevents the blood clotting inside the blood
    • Protective coat : Glycoproteins form a protective layer, glycocalyx, on intestinal
    • Hyaluronic acid : It acts as a lubricating fluid in the synovial joints between the limb
    • Blood antigens like A, B and Rh-factor are glycoproteinaceous and provide immunity to the
    • Sugars are also important components of some glycoproteinaceous hormones like FSH (Follicular stimulating hormone), LH (Luteinizing hormone) FSH controls gametogenesis while LH controls the ovulation and formation of corpus luteum.
    • Carbohydrates may be changed into amino
    • Oligosaccharides of cell membrane help in cellular
    • Cellulose forms roughage of food which stimulates the secretion of digestive juices. It also helps in
    • Cellulose nitrate is used in





  • Carboxy-methyl cellulose is used in cosmetics and
  • Cellulose acetate is used in preparing cellulose plastics, shatter-proof glass, fabrics

Differences between caloric fuel value and physiological fuel value

Characters Caloric fuel value Physiological fuel value
Site of production Energy in kcal produced by the complete combustion of 1 gm. of substance in a bomb calorimeter. Energy in kcal produced by the oxidation of 1 gm. of substance in the body tissues.
Amount of energy 1 gm. of carbohydrates provide 4.1 kcal. of energy. 1 gm. of carbohydrates provide 4.0 kcal. of energy.
  • Lipids and fats : Fats and all fat like substances are called lipids. They are composed of C, H and O. They are insoluble in water but soluble in ether, alcohol, chloroform

(1)  Types of lipids

  • Simple lipids : Examples – Fats in the body in the form of adipose tissues, fatty acids,
  • Complex lipids : Examples – Phospholipids, glycolipids
  • Derived lipids : Obtained by hydrolysis of simple or complex Examples – Cholesterol, ergosterol.

(2)  Specific features

  • Source : Butter, ghee, liver oil, vegetable cooking oil
  • Daily requirement : 50
  • Storage site : Subcutaneous fat, adipose
  • Caloric value : 45 k cal/gm.
  • Actual value : 0 k cal/gm.

(3)  Functions of lipids

  • The fats acts as concentrated fuel. The caloric fuel value of 1 gm of fats is 9.45 kcal, while the physiological fuel value of 1 gm of fats is 9.0 kcal (37 kJ), which is about 2.25 times more than the energy provided by same amount of
  • The fats are also highly suitable for storage as the reserve food It is mainly stored in the liver, beneath the skin, in the brown deposits and in the fat bodies. Normally, the fats constitute about 4% of liver by weight.
  • Fats stored in the subcutaneous tissue insulate the body against the loss of heat energy, so conserve the body Thus, fats help in homeothermy.
  • Medullary sheath is formed of white fatty substance, myelin, which insulates the nerve fibres and prevents the loss of
  • Fats from the protective shock absorbing cushions around a number of organs like the eye balls, kidneys (renal fat), ovaries,
  • These help in the absorption of fat-soluble vitamins like A, D, E and

(c) Proteins : They are composed of C. H. O. N and some of in addition contain S and P. They are complex, versatile, macromolecules with very high molecular weight. Their unit is amino acids. Out of the 20 amino acids, required in human to build proteins, half of them are essential and rest are non-essential amino acid. Essential





amino acids are those, not synthesized by human body and are present in food. The non-essential amino acids are those which can be synthesized by human body.

Amino acids


Dispensable or Essential amino acids Non-dispensable or Nonessential amino acids
*Arginine Glycine
*Histidine Alanine
Isoleucine Serine
Leucine Aspartic acid
Methionine Asparagine
Phenylalanine Cysteine
Threonine Glutamic acid
Tryptophan Glutamine
Lysine Proline
Valine Tyrosine


Arginine and histidine are considered semi indispensable amino acids. These two are not essential in the adult organisms.

  • Classification of proteins : They are following types –

(i)  On the basis of structure of molecules

  • Fibrous : Examples – Collagen, myosin, keratin, fibrin of coagulated blood
  • Globular : Examples – Albumin, globulin, haemoglobin, enzymes, snake venom
    • On the basis of their chemical nature : The proteins are divided into three categories –
  • Simple proteins : These are formed of peptide chains and yield only amino acids on On the basis of shape, these may be fibrous proteins e.g. collagen of white fibres, elastin of yellow fibres, keratin of exoskeletal structures like nails, horns, hoofs, hair, feather etc.; globular proteins e.g. albumins and globulin of blood plasma, protamines, histones, glutelins etc.
  • Conjugated proteins : These are formed of a proteinaceous and a non-proteinaceous prosthetic These include nucleoproteins (of chromosomes-DNA and proteins; and ribosomes-RNA and proteins), glycoproteins (of blood-antigens), phosphoproteins (casein of milk), lipoproteins (lipovitellin of egg-yolk), chromoproteins (haemoglobin of RBCs), haemocyanin, rhodopsin (visual purple), iodopsin (visual violet), cytochromes), metalloproteins (carbonic anhydrase enzyme with Zn2+) etc.
  • Derived proteins : These are formed by the partial hydrolysis of simple proteins and include peptones, proteoses

(2)  Functions of protein





  • Many proteins act as structural proteins and take part in building and repairing of the body tissues so these are essential for the growth, especially for the growing children. These include ossein of the bones, chondrin of the cartilages, collagen of white fibres, elastin of yellow fibres
  • Certain proteins act as functional proteins and regulate the metabolism. These includes enzymes like pepsin, trypsin hormones like insulin, TSH etc., carrier proteins acting as permeases in active transport etc.
  • During the deficiency of carbohydrates and fats, the proteins are hydrolysed into amino acids which act as respiratory fuels to provide the energy. Caloric fuel value of 1 gm of protein is 5.65 while the physological fuel value of 1 gm of proteins is 4.0 kcal.
  • Some proteins take part in the formation of useful products :
  • Globin protein combines with four haem prosthetic groups to form haemoglobin which transports 97-99% of O2 from the lungs to the body
  • Actin and Myosin are main structural and functional proteins of the muscles and help in muscle contraction, so in movements and
  • Rhodopsin and Iodopsin proteins are the components of rod and cone cells respectively and help in night and day vision
    • g-globulins of blood plasma act as antibodies which provide immunity against the
    • Prothrombin and fibrinogen proteins of blood plasma are involved in blood-clotting to prevent excessive bleeding at the
    • Certain proteins of blood act as buffers (g. haemoglobin) which help in the constancy of pH of the body fluids.
    • Amino acids of the proteins may transform into carbohydrates and
    • Exoskeletal elements like epidermal scales of reptiles; feathers of birds; and hair, nails, claws etc. of mammals are formed of keratin These elements are protective in function.
    • Hormone receptors are always proteinous in nature and help in biological response from the target
    • Some proteins act as reserve food g. zein of maize and glutein and gliadin of wheat etc. Thus, the proteins are essential for the body growth. Their acute deficiency in the food causes retardation of physical and mental growth. Deficiency of proteins causes two diseases in infants : marasmus and kwashiorkor.
    • Protein acts as a building material.
    • As an enzymes &
    • As a
    • As a carrier
    • As a component of tissue and cell





  • As a fuel material and biological

(3)  Specific features

  • Source : Chief source is pulses, egg, milk, meat, fish, leafy vegetables, soyabean, groundnut
  • Daily requirement : 70-100 gm.
  • Caloric value : 6 k cal/gm.
  • Physiological caloric value : 4 k cal/
  • Caloric value and Physiological fuel value and complete combustion of one gram of substance produces energy in kcal in a bomb calorimeter is called the caloric value of substance, while complete oxidation of one gram of substance produces in kcal in the body is called physiological fuel value of


Nutrient Caloric value Physiological fuel value
Carbohydrates 4.1 kcal 4.0 kcal
Proteins 5.65 kcal 4.0 kcal
Fats 9.45 kcal 9.0 kcal


  • Nucleic acids : These are compounds of carbon, hydrogen, oxygen, nitrogen and phosphorus. These occur in all body cells and transmit coded informations of all morphological and functional hereditary characteristics from one generation to the next. The molecules of nucleic acids are long-chain polymers of nucleotide monomers. These megamolecules are called polynucleotides. These are the largest and most complex molecules of

Nucleic acids are of two types : Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Only nine types of nucleotide monomers occur in cells; only four of these link by “phosphopdiester bonds” forming polynucleotide chains (megamolecules) of DNA and another four of RNA. Each nucleotide is itself a complex molecule formed by linking of a nitrogenous base, a pentose sugar and a phosphate group. “Phosphodiester bonds” are also dehydration or condensation linkages. Hence, in digestion, nucleic acids of food are hydrolysed first into nucleotides. Then the nucleotide molecules are further degraded to their component nitrogenous bases, pentose sugars and phosphate groups.

  • Water : Water is an essential constituent of protoplasm, which forms the physical basis of life, though it does not yield any The water is an inorganic compound, composed of hydrogen and oxygen in the ratio of 2 : 1. Protoplasm has nearly 90% water, but the human body has approximately 60–70% of water.

(1)  Functions

  • Water act as a best
  • Involve in so many metabolic
  • Act as temperature
  • Remove excess of body heat through





  • It also act as dispersion medium ioniser, diffusion

(2)  Specific features

  • Sources : Metabolic water, liquid food and drinking
  • Daily requirement : 5- 6 glasses (4-5 litre).

(f)  Vitamins

  • Historical review
    • I. Lunin (1881) discovered vitamins.
    • The term ‘vitamin’ was first used by Funk in
    • Hopkins and Funk (1912) propounded a ‘vitamin theory’.
  • Definition : Vitamin are complex organic compounds needed daily in minute quantities and act as growth and metabolic regulatory
  • Sources : Vitamins can only be synthesized by green plants, hence animals depend for their vitamin requirement upon the Human body manufactures vitamin D using ultraviolet rays of sunlight and can store A, D and B12. The chemical compositions of vitamins are known and it is possible to synthesize them.
  • Importance : The vitamins are not a sources of They regulate the various metabolic processes. They mostly act as the constituents of coenzymes in the cells.
  • Type : Vitamins are divided into two groups –
    • Fat soluble vitamin : A, D, E and K.
    • Water soluble vitamin : B complex and C.


Fat soluble vitamins


Name of vitamins and chemical formula  






Daily requirement per day Functions Name of Deficiency Disease  



Other Features
Vitamin A or


Retinol or anti xero-phthalmic or anti infection vitamin

C 20 H 29O

Mc-Collumn and Davis (1913) Vegetables butter liver oils egg yolk, mango and orange, carrot. 2 mg Part of visual pigment, maintenance of epithelia and prevention of keratini-zation of epithelium. Xerophthalmia Night blindness or nyctalopia Keratomalacia.


–          Drying of eyeball

–          Unable to see in dim light

–          Epithelium keratinised

Synthesized and stored in the liver.

Destroyed by – strong light.

            –      Dry scaly skin  





Vitamin D or


Ergocalciferol or sunshine vitamin or anti rachitic vitamin

 C28 H 44 O

Steenbock and Hess 1924) Cod liver oil, butter, fish, eggs, milk, brain, lung, and spleen. 0.01 mg Facilitates absorption of calcium and phosphorus by intestine and their retention in body and deposition in bones. Rickets in children



Osteomalacia in adults.

Deformities of bones like bowlegs pigeon chest

Weak bones liable to easy fracture

Synthesized in the body on exposure of skin      (7- hydroxy cholesterol)

to light.


Destroyed by – oral contraceptives

Vitamin E or


a Tocopherol

or anti sterility vitamin

 C29 H50 O2

Evan and sore


Fresh green vegetables, meat, yolk, vegetable oils, butter and cheese, peanuts 20 mg Antioxidant and some role in ETS. Anaemia Sterility






Muscular atrophy

Destruction of RBC.

In male causes sterility and in female abortion may occur of offspring. Effect not proved in man.

Destroyed by UV

– rays.


It is also used for curing tumour and cancer

            Degeneration of muscles  
Vitamin K or


Phylloquinone or

anti haemorrhagic vit-amin

 C31 H 46 O2

Dam and Droisy (1935) Fresh green vegetables. to matoes, liver, soyabean, cheese, egg. 0.07 – 0.14 mg Synthesis of prothrombin for normal clotting of blood. Haemorrhage Reduced ability of blood to clot and also leads to haemorrhages. Vitamin K is synthesised by intestinal microbes present in the intestine.

Destroyed by– prolonged use of antibiotics.



Water soluble vitamins


Name of Vitamins and Chemical Formula Discovery Sources D.R. Function Name of Deficiency Disease Symptoms Other Features
Vitamin B1 or Thiamine or anti neuritic or antiberiberi

 C12 H16 N 4 SO

C. Funk (1926) Branrice, whole wheat flour, egg, meat, liver yeast etc. 1-1.5 mg Act as co- enzyme in cellular respiration, role in nutrition of nerve cells. Beri- beri – or Dry beri – beri (man)

Polyneuritis or (animals) wet

beri – beri

Loss of appetite and weight, retarded growth, muscular dystrophy.

Nerves to become

Beri-beri disease was discovered by Eijkman

Destroyed by – cooking

      Essential for

carbohydrate metabolism,

Cardiovascular atrophy extremely irritable. Heart enlargement  
      protein synthesis      
      and control      
      water balance in      





Vitamin B2 or G or yellow enzyme or Riboflavin or Lactoflavin or ovaflavin or hepatoflavin

C17 H 26N 4O 6

Warburg and Christain Cheese, egg, yeast, meat, liver, cereals, green, vegetable. 1-2 mg Required for cell growth.

Form pair of coenzyme (FMN, FAD).




Glossitis Keratitis

Cracking of skin at corners of mouth

Inflammation of tongue

Inflammation of skin

Stored in liver, Excess of this is eliminated in urine.

It is associated with the physiology of vision

Vitamin B3 Yeast factor or pantothenic

acid or anti

graying factor on chick antidermatitis factor

 C9 H17 O5 N



All foods, more in yeast, kidney, liver, egg, meat, milk, ground nut 5-10 mg Part of co- enzyme A. needed for cell respiration, necessary for normal skin and nerves. Burning feet syndrome,

Nervous disorder


Nerve degeneration

It occurs in all types of plants and animal tissues.

Its deficiency cause graying of hair

Vitamin B5 or Niacin or Nicotinic acid or pellagra preventing


Goldberger (1912) Fresh meat, liver, fish, milk, cereals, pulses, yeast etc. 16-20 mg It is an essential component of NAD and NADP thus form coenzymes, metabolism of carbohydrates, functioning of gastrointestinal tract and nervous system Pellagra, Dermatitis,


Diarrhoea Dementia

Rough skin



Inflammation of skin which becomes scaly

and papillated

It is characterised by 3D’s i.e. dermatitis diarrhoea and dementia

Destroyed by –

 C6 HNO2     Death

(4-D syndrome)


Neural deterioration which may lead to madness


Pellagra preventing factor Goldberger also called Goldberger’s p-p


          It is also synthesized by
          colon bacteria
Vitamin B6 or pyrido-xine or Rat anti dermat-ities factor

 C8 H11O3 N  

Gyorgyi (1928) Brewer’s yeast, liver, egg, yolk, kidney, milk, and vegetables. 2 mg It is essential component of coenzyme pyridoxal phosphate. It promotes growth in rats used for curing


Anaemia Dermatitis, paralysis &

death of rats.




Mental disorder

Nausea, lack of RBC (blood) Disturbance of

central nervous

system Skin leisons

Term B6 was

coined by Gyorgy. Destroyed by – cooking and oral


Vitamin H or

 B7 or Biotin

Bateman and

Allison (1916)


vegetables and

150-300 mg It acts as

coenzymes and

Dermatitis Scaly and itchy


It is synthesized by

intestinal bacteria

or coenzyme R or Avidin

 C10 H16 N 2 O3 S

  egg yolk   essential for fat synthesis and energy production.     Destroyed by – prolonged use of antibiotics





Folic Acid or Vitamin M or folacin or Anti anaemic factor Day (1935) Green vegetable (spinach) Banana, orange and Liver. 0.4 mg It forms coenzymes and play essential role in cell metabolism, Necessary for erythropoiesis, required for DNA synthesis. Megaloblastic anaemia.


Enlarged RBCs Ulceration of mouth It is also synthesized by intestinal bacteria

Destroyed by – cooking

Vitamin B12 or Cyanocobalam ine or Animal protein factor (APF) or

Intrinsic factor of castle


Rickets (1948) Meat, egg, liver, fish, synthesized by intestinal bacteria. 0.003 mg Required for chromosome duplication and formation of blood corpuscles. Pernicious anaemia Reduced formation of erythrocytes in bone marrow It is also known as anti pernicious factor

Also synthesized by intestinal bacteria in human colon

Destroyed by – excessive heat

Vitamin C or Ascorbic Acid

 C6 HO6

Szent Gyorgyi


Citrus fruits such as lemon, mango, amla, plumes, guava. 40-60 mg Functions as part of oxidation- reduction system.

Helps in secretion of collagen cement


Scurvy. Spongy and bleeding gums, fragile blood vessels and bones. Required by primates, all other vertebrates and some other invertebrates can synthesize vitamin

C. It is the earliest known vitamin.

        Helps body to develop resistance to diseases.     It is wound healing vitamin. Destroyed by – Heating
        Helps in absorption of Ca and Fe in the


        Wound healing.      


Name of Vitamin Function Symptoms of deficiency
Inositol or mouse antialopecia factor Stimulate growth of mice. Spectacle-eye condition in rat can be treated keep a limit on the cholesterol level in the blood of man. Causes reduced growth and alopecia (loss of hair) in the mice. Also causes hemorrhagic degeneration of the adrenal gland.
Choline It is an important lipotropic factor which prevent excessive development of fatty liver. It takes part in the formation of acetylcholine which involved conduction of nerve impulse. Chronic deficiency causes cirrhosis in the liver also causes haemorrhagic changes in kidney.
Vit.P or citrin Control the permeability and fragility of the capillary wall to plasma protein. Its deficiency causes subcutaneous bleeding due to break down of capillary walls.


  • Minerals elements : They forms approximately 5% of body weight. They are essential to regulate the various metabolic activities of the animals. The various type of mineral are group into two categories as minor Examples – Ca, S, P, Na etc. and trace element examples – Cu, Zn, Mn etc. Some of these minerals are described as follows –





Chart of important minerals required in animal bodies


Mineral elements Sources Significance Effects of deficiency
Minor elements

(1) Calcium–Ca

Milk, Cereals, Cheese, Green

Vegetables, Pods.

Required for formation of teeth and

bones, blood clotting, functions of nerves and muscles.

Weak teeth and bones; retarded body


(2) Phosphorus–P Milk, Meat, Cereals. Required for formation of teeth and bones

and acid-base balance; component of ATP, DNA, RNA.

Weak teeth and bones; retarded body growth

and physiology.

(3) Sulphur–S Many proteins of food. Component of many amino acids. Disturbed protein metabolism
(4) Potassium–K Meat, Milk, Cereals, Fruits and


Required for acid-base balance; water

regulation and function of nerves.

Low blood pressure, weak muscles; risk of


(5) Chlorine–Cl Table Salt. Required     for      acid-base    balance;

component of gastric juice.

Loss of appetite; muscle cramps.
(6) Sodium–Na Table Salt. Required for acid-base and water balances

and nervous functions.

Low blood pressure, loss of appetite; muscle


(7) Magnesium–Mg Cereals, Green Vegetables. Cofactor of many enzymes of glycolysis

and a number of other metabolic reactions dependent upon ATP.

Irregularities of metabolism, principally

affecting nervous functions.

(8) Iron–Fe Meat, Eggs, Pods, Cereals,

Green Vegetables.

Component    of     haemoglobin   and


Anaemia weakness and weak immunity.
(9) Iodine–I Milk, Cheese, Seafood, Iodized


Important   component    of     thyroxin

hormone and regulate metabolism of cell.

Goitre, cretinism.
Trace Elements

(10) Fluorine–F


Drinking water, Tea, Seafood


Maintenance of bones and teeth.


Weak teeth, Larger amount causes mottling of teeth.

(11) Zinc–Zn Cereals, Milk, Eggs, Meat,


Cofactor of digestive and many other


Retarded growth, anaemia, rough skin, weak

immunity and fertility.

(12) Copper–Cu Meat, Dry fruits, Pods, Green

Vegetables, Seafood.

Cofactor of cytochrome oxidase enzyme.

Necessary for    iron    metabolism and

development of blood vessels and connective tissues.

Anaemia, weak blood vessels and connective

tissue and damage to central nervous system.

(13) Manganese–Mn Dry fruits, cereals, Tea, Fruits

and Green Vegetables.

Cofactor of some enzymes of urea

synthesis and transfer of phosphate group.

Irregular growth of bones, cartilages and

connective tissues.

(14) Cobalt–Co Milk, Cheese, Meat. Important component of vitamin B12 Anaemia.
(15) Selenium–Se Meat, Cereals, Sea food. Cofactor of many enzymes; assists vitamin E. Muscular pain; weakness of cardiac muscles.
(16) Chromium–Cr Yeast, Seafood, Meat, Some


Important for catabolic metabolism. Irregularities of catabolic metabolism and

ATP production.

(17) Molybdenum–Mo Cereals, Pods, Some Vegetable Cofactor of some enzymes. Irregular excretion of nitrogenous waste


Important Tips





  • Camel can live without water for a considerable day, as it uses its metabolic water, which comes from of the oxidation of fats present in
  • Zinc is necessary to maintain plasma concentration of vitamin
  • Tea/Coffee inhibit the absorption of iron from the Prolonged consumption of tea/coffee after meal can lead to iron deficiency anemia.
  • Vertebrates cannot digest keratin protein of hair, nails, fibroin protein of silk fibers etc, but certain insects can digest these proteins so damages silken and woolen
  • Dyspopsia – Indigestion due to defective
  • Vitamin C was the first vitamin to be produced during fermentation process using wild
  • An alcoholic is always deficient of vitamin
  • Excessive intake of vitamin A causes bone reabsorption and
  • Some of the bacteria including Escherichia coli present in the large intestine or colon produce vitamin k, which is absorbed by the host and this is probably the main source of this vitamin for
  • Vitamin B17 is a recently discovered vitamin with anti–cancer
  • Most of the B-complex vitamins are
  • Presently vitamin B12 is produced directly during the course of fermentation by propioni bacteria and certain strains of
  • Vitamins, which are synthesized by the intestinal flora are vitamin Thiamine, Riboflavin, Pantothenic acid, Niacin, Pyridoxin, Biotin and Folic acid.
  • Overcooking, excessive alcohol, tobacco and coffee, certain medicine destroys vitamin.
  • Effect of the reflex action due to the taste of food is the release of vagal
  • Gama – linolenic acid and arachidonic acids are essential fatty acid in
  • Glycine is simple amino
  • Phenyl alanine amino acid is denoted by symbol
  • Vitamin nicotinamide functions as reducing
  • Vitamin ‘D’ is a steroid
  • The overdosage of vitamin ‘A’ causes injury to
  • Vitamin ‘C’ is present in large amount in the body in adrenal
  • Vitamin B6 is essential for
  • Deficiency of vitamin H (biotin) cause rise of blood
  • Frog tadpole is delayed in metamorphosis due to less amount of iodine in
  • The most complex amino acid having double rings structure is
  • The intestinal bacteria are able to synthesize both essential amino acids and vitamins in
  • Proteins which contain most of the essential amino acids are termed first class, while those do not, are called second
  • Animal proteins are mostly first class and plant proteins are second class
  • Whiptail disease is caused due to the deficiency of

Composition of milk


Species Water Protein Fat Lactose
Camel 87.2 3.7 4.2 4.1
Cow 87.2 3.5 3.7 4.9
Buffalo 78.6 5.9 10.4 4.3
Goat 86.5 3.6 4.0 5.1
Human 87.5 1.0 4.4 7.0


Balanced diet for moderately active adult Indian


Name of food Recommended amounts (gms. per day)
Adult man Adult woman
(1) Cereals (Wheat/Rice) 520 440
(2) Pulses 50 45





(3) Milk 200 150
(4) Meat/Fish or Egg 30 30
(5) Fats (Oil, Butter, Ghee) 45 25
(6) Sugar/Molasses 35 20
(7) Root and Tubers (Raddish, Potato, etc.) 60 50
(8) Green leafy vegetables 40 100
(9) Other vegetables 70 40


  Nutritional imbalances and disorders.

  • Balanced diet : The diet which contain the various nutrients in such proportions as can satisfy all the various needs of our body, is called a “balanced diet”. The proportion of carbohydrates, proteins and fats into fulfill energy requirement is 4 : 1 : 1 e. 65% of energy is obtained from carbohydrates and 10–20% each from proteins and fats. This amount of energy is fulfilled by intake of 400–600 gm of carbohydrates, 80–100 gm of proteins and 50–60 gm of fats. The balanced diet must also contain sufficient amount of minerals and vitamins.

(ii)  Metabolic rates

  • Basal metabolic rate : Amount of energy required daily by a person to maintain its basal metabolism and is about 1600 k cal/day.
  • Routine metabolic rate : Amount of energy required daily by a person to do his routine work. It is about 2800 k cal/day for males and 2300 k cal for
  • Active metabolic rate : Amount of energy required daily by a person to maintain its high metabolic rate during heavy physical work and is about 6000 k cal/day for males and 4500 k cal for females. It has been scientifically determined that a child of 4–6 years approximately requires 1500, a child of 13–15 years requires 2500 and a youth of 16–18 year requires 3000 k cal of energy per day. The average metabolically available energy for each gram of carbohydrate is 0 k cal, for proteins is 4.0 k cal and for fats, it is 9.1 k cal.
  • Nutritional disorders : Every organism requires an adequate supply of nutrients in proper proportion in their diet for proper growth and There are two types of nutritional disorders
  • Under nutrition (malnutrition)
  • Over nutrition

(a)    Diseases due to deficiency of nutrition (malnutrition)



Name of the Deficiency Deficient Nutrient Symptoms
Anaemia (microcytic) Fe Haemoglobin and number of erythrocytes gets reduced.
Megaloblastic anaemia Folic acid and B12 Presence of immature erythrocytes in blood.
Pernicious anaemia Vitamin B12 Immature RBC without Hb. This may be fatal unless treated with vitamin

B12 injection.

Xerophthalmia Vitamin A Thickened, keratinised, opaque ulcerated cornea. Prime cause of





    blindness in India, especially among children.
Night Blindness Vitamin A Less rhodopsin in rod cells of retina. So no vision in dim light.
Rickets (in children) Vitamin D Weak, soft, thin bones due to poor deposition of Ca and P. Bent long bones and painful swelling on wrist, elbow and knee joints.
Osteomalacia (adults) Vitamin D Weak bones of vertebral column, pelvis gets bent and deformed by body weight.
Sprue Folacin Ulceration of mouth, inflammation of bowel, indigestion, diarrhoea, weakness.
Pigeons breast Vit. – D Incomplete ossification at the end of limb bone, deformed ribs leading to pigeons breast.
Beri – beri Vitamin B1 (Thiamine) Reduces aerobic carbohydrate metabolism. So peripheral nerves inflammed causing pain, numbness and weakness of limb muscles. Paralysis.

Fluid accumulation in tissues or oedema of hands and legs. Cardiac oedema.

Scurvy Vitamin C Fragile blood vessels because of defective collagen fibres in their walls. Bleeding gums, teeth fall, bones fragile. Wound healing delayed, vitamin C recommended in serious injury.
Bleeding disease

(Hypoprothrombin anaemia)

Vitamin K Delayed blood clotting (s) so profuse bleeding.
Marasmus Protein / Malnutrition Growth and replacement of tissue proteins imparted so emaciated body with their limbs and prominent ribs, dry, thin and wrinkled skin, Diarrhoea.
Kwashiorkor Protein Wasting muscles, thin limbs, Retarded growth of body and brain, Oedema, Diarrhoea.
Pellagra Nicotinamide Swollen lips, thick pigmented skin of hands and legs. Irritability.
Osteoporosis Ca Weakning of bones, tooth decay.
Goitre I2 Enlargement of thyroid gland.
Muscular cramps NaCl Pulling of muscles due to dehydration.
Dental cramps Fluorine Tooth decay.

Daily Dietary Requirements of Nutrients (Recommended by Indian Council of Medical Research)

Individual Tot al kca


Protei n (gms.) Calciu m (gms.) Iron (mgs


Vitami n A (mg.) Thiam in (mgs) Riboflav in (mgs.) Niacin (mgs.) Folaci n (mg.) Vitami n B12


Vitami n C (mgs.) Vitami n D (IU)
(1) Man Moderately active 280


55 0.4-0.5 24 750 1.4 1.7 19 100 1 40  
(2) Woman 220 45 0.4-0.5 32 750 1.1 1.3 15 100 1 40  
(i)     Moderately 0 59 1.0 40 750 1.3 1.5 17 300 1.5 40
active 270                    
(ii) Pregnant 0 70 1.0 32 1150 1.4 1.6 19 150 1.5 80
(iii) Lactating                      





(3) Boy

(16-18 years)



53 0.5-0.6 25 750 1.4 1.7 19 100 1 40 200
(4) Girl

(16-18 years)



44 0.5-0.6 35 750 1.1 1.3 15 100 1 40 200


(b)  Diseases due to over nutrition

  • Fluorosis : Caused due to excess of It results in tooth and bone decay.
  • Obesity : This is over–nutritional It is caused when “energy inputs exceeds energy output”. It results in deposition of excess fat in the body.
  • Constipation : Slow movement of faeces down the large intestine causes accumulation of dry and hard stool is It is generally caused by irregular bowel habits.
  • Diarrhoea : Rapid movement of faecal matter down the large intestine causes loose stools called It may be also caused by viral or bacterial infections of intestinal tract, particularly of large intestine and by nervous tension.
  • Piles or haemmorhoids : Enlargement of the anal It may be either hereditary or may be caused due to rapid changes in the diet.
  • Hypercholesterolemia : Caused due to excess of saturated fats like butter, ghee, hydrogenated vegetable oils and eggs It results in increased level of cholesterol in blood, arteriosclerosis, coronary thrombosis, heart attack etc.
  • Hypervitaminosis A : It results in loss of appetite, body hairs, painful swelling etc.
  • Hypervitaminosis D : It results in deposition of calcium ion in the soft tissues of the

Differences between Kwashiorkor and Marasmus


Kwashiorkor Marasmus
(1) It is caused by deficiency of protein in the diet. (1) It is caused by prolonged deficiency of proteins and calories in the diet.
(2) It commonly affects babies between 1-3 years of age. (2) It affects infants under one year of age.
(3) Subcutaneous fat persists. (3) Subcutaneous fat is used up, making ribs very prominent.
(4) Oedema affects legs and face. (4) No oedema occurs
(5) Skin and hair change colour. (5) No change in skin and hair colour.
(6) Body becomes under weight. (6) Body becomes very under weight.
(7) Appetite is reduced. (7) Appetite is not effected.
(8) Patient needs proteins to recoup. (8) Patient needs proteins as well as carbohydrates and fats to recover.


 Regulation of food intake.

  • Hunger : Hunger is defined as the intrinsic (involuntary) desire or craving for Hunger is associated with a number of objective sensations. For instance, food deprival for many hours causes intense rhythmic hunger contractions in stomach, which even causes intense pain (hunger pangs) send sensory impulses to a “hunger or feeding centre”, located in the lateral regions of hypothalamus.





When glucose levels fall in blood, hunger centre stimulated. Hunger centre transmits impulses to wall of stomach and wall of empty stomach start contraction or hunger pangs. After taking meal satiety centre which located in hypothalamus stimulates and feeding is stopped. During high fever person does not feel like taking meal because high temperature shuts off the appetite centre.

  • Thirst : Subconscious desire for water is called It is also induced by a hypothalamic “thirst centre”. When amount of water decreases in body fluids (blood, lymph, tissue fluid, cerebrospinal fluid etc.) due to fever, exercise and sweating, copious urination, diarrhoea, etc. This induces the feeling of thirst. Presumably, a fall in glucose level in the blood also induces thirst.
  • Theory of regulation of food intake : They are following –
  • Neuronal theory : According to this theory, two different type of centers are present in the hypothalamus which regulates These centre are appetite and satiety. Appetite centre is often used to imply a conscious desire for specific or selected type of food. Interoceptors of stomach wall, stimulated by the muscular contraction, send sensory impulses to the hunger centre located in the lateral region of hypothalamus. Satiety is the conscious sensation of food sufficiency leading to a voluntary cessation of eating. The centre is located in the ventromedian regions of hypothalamus.
  • Glucostatic theory : When the blood glucose level decreases we feel hungry. It is also caused due to low level of amino acids and fatty acids, and when the level of these substances increases in blood, satiety centre
  • Thermostatic theory : Decrease in body temperature increases hunger due to increased metabolic Conversely, an exposure to heat, or increases in body temperature reduces hunger due to decreased metabolic rate. These conditions are caused by interactions between hypothalmic temperature regulating and food intake– regulating system.
Leave a Reply

Your email address will not be published.