Chapter 8 Structural Organisation in Animals Part 2 by TEACHING CARE online tuition and coaching classes

Structural organization in animals Part 2

 

Blood Cells – Leukocytes

 

Leukocytes (white blood corpuscles or WBC) do not have hemoglobin and hence are colourless. Leucocytes are nucleated cells. They are o two major classes : granulocytes (with cytoplasmic granules) and granulocytes (without granules).

Granulocytes are of three types, viz. neutrophils, eosinophils and basophils, each with a lobed nucleus. Agranulocytes are of two types, viz. lymphocytes and monocytes. Neutrophils and monocytes protect the body against microbes by phagocytosis. Lymphocytes produce antibodies in the blood to destroy microbes and their toxins. The number of leucocytes per microlitre (1 l = 1 mm3 = 10-6) of blood is called the Total Count of WBC. It is normally 5000 in humans. It may rise abnormally in acute infections (e.g., pneumonia), inflammations (e.g., appendicitis) and malignancies (e.g., leukemia). In some cases such as folic acid deficiency, the total count falls abnormally (leucopenia). The total count of WBC is also of diagnostic value in some diseases. Monocytes have kidney shaped nucleus. The process by which monocytes and neutrophil squeeze through thin capillary wall is called Diapedesis.

 

Differential Leukocyte Count (DLC) Leukocytes (2 types):

 

1. Granulocytes with granules in cytoplasm

(3 types) on the basis of staining characteristic of cytoplasmic granules and shape of nucleus

1. Neutrophils (40 – 75%)
2. Eosinophils (1 – 6%)
3. Basophils (0 – 1%)

 

2. Agranulocytes without granules

 

1. Monocytes (2 – 10%)
2. Lymphocytes (20 – 45%)

 

1. Neutrophils: They are maximum in number, stain equally with both basic and acidic dyes and haved many lobed nucleus, granules are in abundance in cytoplasm and help in phagocytosis.

 

1. Eosinophils: They have bilobed nucleus, stain with acidic stains. Their number increases during allergic reactions (Eosinophila).

 

1. Basophils: They stain with basic dyes. The nucleus is ‘S’ shaped. Coarse granules are few in cytoplasm. Basophiles release heparin and histamine in the blood and have a function similar to the mast cells.

 

1. Lymphocytes have large and rounded nucleus. The cytoplasm forms a thin peripheral film. They have the stain cells in the bone marrow and are differentiated in the bone marrow or in the thymus. Lymphocytes are of two types B-lymphocytes and T-lymphocytes.B-lymphocytes produce antibodies against antigens and they mature in the bone

 

1. Monocytes are the largest leucocytes (12-15 m). The nucleus is kidney They are produced from bone marrow from monoblast cells. They help in phagocytosis.

 

 

Differences between different types of Leucocytes

 

Character	Lymphocytes	Monocytes	Eosinophils	Basophils	Neutrophils (Acidophils)
Number/Percentage	20-25%	2-10%	2-3%	0.5-1%	60-65%
Granules in cytoplasm	Absent	Absent	Coarse	Coarse	Fine
Staining of cytoplasm	Basophilic	Basophilic	Eosinophilic	Basophilic	Neutrophilic
Nucleus	Rounded	Bean-shaped	Bilobed	S-shaped 3-lobed	Multilobed
Site of formation	Lymph nodes spleen, thymus tonsils, Peyer’s patches Bone marrow	Bone marrow	Bone marrow	Bone marrow	Bone marrow
Life span	Few days or even years	10-20 hours in the blood tissue, months or even years	4-8 hours in blood and 4 to 5 days in tissue	4-8 hours in blood and 4 to 5 days in tissue	4-8 hours in blood and 4 to 5 days in tissue
Function	Antibody formation	Phagocytic	Important role in immunity antiallergic	Secretion of heparin histamine and serotonin	Phagocytic

Blood platelets

 

Blood platelets also called throbocytes, are non-nucleated, round or oval, biconvex disc-like bodies. They are 2-3 micromitres in diameter and their number normally varies from 0.15 to 0.45 million per microlitre of blood. They bud off from the cytoplasm of very large Megakaryocyte cells of bone marrow. Their normal life-span is about a week. When a blood vessel is injured, platelets get clumped at the injured spot and release certain chemicals called Platelet Factors. These promote blood coagulation.

 

Thrombocytopenia, decrease in platelet count. Purpura, is a group of bleeding disease due to thrombocytopenia

 

Blood Coagulation

 

When blood oozes out of a cut, it sets into gel within a few minutes. This is called coagulation. Coagulation is brought about by hydrolysis of soluble fibrinogen of plasma to insoluble fibrin. This is catalyzed by an enzyme called thrombin. Fibrin precipitates as a network of fibres. This network traps many blood cells, particularly RBC’s to form a red solid mass called the Blood Clot. The clot seals the wound in the vessel to stop the bleeding. The straw-colored fluid left after clotting of blood, is called Serum. The serum can not be coagulated as it lacks fibrinogen.

 

Thrombin occurs in normal blood as an inactive globulin called Prothrombin. It must be activated to thrombin before blood coagulation can occur. In case of injury to a blood vessel, coagulation promoting substances called Thromboplastins are released into the blood from clumped platelets and damaged tissues. Thromboplastins help in the formation of the enzyme Prothrombinase. This enzyme hydrolyses prothrombin to thrombin to initiate coagulation. Ca²⁺ ions are essential for both the activation and action of thrombin.

 

Blood normally contains an anticoagulant, Heparin which prevents activation of prothrombin, heparin is released from mast-cell granules. Blood also contains Antithrombin which inhibits any thrombin formed accidentally.

 

Blood drawn from a blood vessel can be kept uncoagulated by adding a pinch of oxalate (sodium or potassium oxalate) to it. Oxalate precitates Ca²⁺ and consequently prevents coagulation. Chilling of blood also delays coagulation because cold depresses the action of coagulation promoting enzymes.

 

Blood Clotting Factors

 

These factors are designated by Roman numerals.

 

 

International Nomenclature	Description
Factor I	Fibrinogen, soluble plasma protein, MW 3,30,000; plasma level 250-400 mg%.
Factor II	Prothrombin, MW 69,000; plasma level 40 mg%.
Factor III	Thromboplastin or tissue factor or tissue extract.
Factor IV	Ionic calcium. Removal of Ca2+ by potassium oxalate, sodium citrate or sodium edetate (EDTA, Versene) prevents clotting in vitro.

 

Factor V	Labile factor or proaccelerin or accelerator globulin. It gets consumed during clotting and is, therefore, absent from serum.
Factor VI	Unidentified.
Factor VII	Proconvertin or serum prothrombin convergen accelerator (SPCA) or stable factor or Autoprothrombin I. Not consumed during clotting and, therefore, is present in serum as well as in plasma.
Factor VIII	Antihemophilic factors (AHF) or Antihemophilic globulin (AHG) or antihemophilic factor-A (AHF-A). It is consumed during clotting, therefore, absent from serum; half life 10-20 hours.
Factor IX	Christmas factor or plasma thromboplastin component (PTC) or autoprothrombin II or AHF-B.
Factor x	Stuart power factor or autoprothrombin-C. Present in plasma and serum.
Factor XI	Plasma thromboplastin antecedent (PTA) or AHF-C. present in plasma and serum both.
Factor XII	Hageman factor or glass factor or contact factor, present in plasma and serum both.
Factor XIII	Fibrin stabilizing factor or fibrinrase or Laki-Lorand factor. It causes polymerization of soluble fibrin to produce insoluble fibrin

Blood Groups

 

ABO Blood Group Karl Landsteiner reported first time ABO blood groups in human beings. A,B and O blood groups were discovered by Landsteiner (1900) while AB blood group was found out by de Castello and Steini (1902). Aggluinogens (=antigens) are present on the surface of red blood corpuscles and agglutinins (=antibodies) are found in the blood plasma. Both antigens and antibodies are proteins. When two different type of blood are mixed, the red blood corpuscles form a clump. The clumping of red blood corpuscles is called agglutination.

 

Agglutination is due to the interaction of antigens and antibodies. There are two kinds of antigens that are named A and B. There are also two kinds of antibodies which are called a and b. Then antigen A and antibody a are incompatible (antagonistic) and cause self clumping and cannot exist together. Thus A and B can exist together and therefore, B and a can exist together. The corpuscles factor a and B can occur together if their antagonistic plasma factors a and b are not present. The plasma factors a and b can occur together if their antagonistic corpuscle factors A and B are absent.

 

Incompatibility during pregnancy : The incompatibility of blood groups of mother and foetus may cause problems during pregnancy. For example, if the mother’s blood group is A and the Foetus’s blood group is B, the antibodies b (plasma factor b) of the mother blood plasma attack and destroy same foetal red blood corpuscles. This may cause anaemia, jaundice, etc. in the baby and is called haemolytic disease of the new-born. It is a mild disorder and rarely needs blood transfusion

2.  Muscular tissue:-

Muscle cause movements of limbs and internal organs and also locomotion of the organism. Cells of muscle tissue can shorten forcefully and again return to the relaxed state. This specialized property is called Contractility. It is based on the organized arrangement of some protein filaments in the

 

cytoplasm of muscle cell. The cell shortens or relaxes according to the relative positions of dofferent intracellular filaments. Whenever adequately stimulated, muscle cell respond by contracting. This property of the muscle tissue is responsible for the various movements in an animal. Muscle cells are usually called Muscle Fibres because they are thin and elongated. In higher animals, some muscles remain associated with the skeleton, but many others form walls of visceral organs, blood vessels and heart. Muscle tissue may be classified into striated, non-striated and cardiac muscles, according to their structure, location and functions.

 

Striated/Skeleton/Voluntary muscles:-

 

 

 

 

Striated/Skeleton/Voluntary muscles are attached to bones by tendons. A voluntary muscle is composed of long bundles of striated muscle fibres. Each fibre is long, unbranched, cylindrical cell. It shows transverse striations in the form of regular alternate dark (A) and light (I) bands. At the centre of I band is a fine, dense, dark band, the Z band or Z-line (Krause’s membrane). The plasma membrane covering the fibre is called Sarcolemma. The cytoplasm inside the fibre is called Sarcoplasm. The sarcoplasm contains many long, thin, unbranched, cross-striated cylindrical structures called Myofibrils. They are arranged along the long axis of the fibre. Dark A bands of neighbouring myofibrils are located side by side, So also are their light I bands. This gives cross-striated appearence to the entire muscle fibre also. A-band has both actin and myosin filaments. The portion of A-band, where actin filaments are absent is called H-zone. Z-zone or Krauze membrane is a dark membrane which bisects I band or

 

isotropic band.

 

Muscle is rich in proteins. Most of these protein occur as two types of filaments arranged longitudinally in myofibrils. The thick filaments are made up of the protein Myosin. Myosin filaments are located inside A bands. Thin filaments are most numerous. They are composed of the protein Actin. From a fine, dense, dark Z band at the centre of each I band, actin filaments extend through the I band and encroach between myosin filaments upto a considerable distance into the A band. Each segment of the myofibril from one Z band to the next functions as a contractile unit and is called a Sarcomere.

 

Various parts of a sarcomere have a specific arrangement of actin and myosin filaments as given below.

 

I band – Has only actin filaments

A band – Has both actin and myosin filaments

H band – Has only myosin filaments

Z line – A membrane to which actin filaments are attached on both the sides.

 

1. Non-Striated or Smooth muscle fibres do not show cross-striations, instead, they look Smooth muscles can not be moved voluntarily. So they are also called Involuntary Muscles. Functionally smooth muscles are of two types. Single-Unit Smooth Muscles are composed of muscle fibres closely joined together. All its

 

fibres contract together as a single unit. They may contract automatically and rhythmically. Such smooth muscles occur on the walls of hollow visceral organs such as the urinary bladder and the gastrointestinal tract. Multi-Unit Smooth Muscle are composed of more independent muscle fibres, not so closely joined together. Individual fibres of such smooth muscle contract as separate unit. These occur at hair roots, and on the wall of large blood vessels e.g., Erector pili muscles.

 

Smooth muscle fibres elongated spindle-shaped cells. They are packed parallel to each other in branching bundles. Each fibre contains a single, spindle shaped nucleus at its thick central part. The smooth muscle fibre is generally shorten than a striated muscle fibre. Mitochondria and other organelles are less extensive and protein filaments are not regularly arranged to give rise to striations.

 

 

 

Table IV : Differences between Single-unit and Multi-unit Smooth Muscles
Single-unit smooth muscles	Multi-unit smooth muscles
(i)    They have number of muscle fibres closely joined together.   (ii)    All the fibres contract together as a single unit, automatically. e.g., walls of hollow visceral organs like stomach, intestine, urinary bladder etc.	(i)    They have number of muscle fibres not so closely joined.   (ii)    The individual fibres contract as separate units more or less as independent muscle fibre. e.g., hair roots, and on the walls of large blood vessels.

 

1. Cardiac muscle occurs exclusively in the heart. It possesses considerable automatic rhythmicity and generates its own wave of excitation. The excitation can also pass directly from fibre to fibre in the cardiac muscle. It is not under voluntary control. It shows cross-striations, but striations are much fainter than those of striated muscle. Between the cardiac fibres intercalated are present. They are specialized regions of cell membrane of two adjacent fibres. The intercalated discs function as boosters of contraction wave and permit the wave of contraction to be transmitted from one to another.

 

Cardiac muscle cells are short cylindrical cells joined end to end to form rows. They possess abundant cytoplasm with myofibrils (sarcoplasm) and numerous mitochondria and glycogen granules.

 

This is because they need a large amount of energy. Faint but regular, alternate dark and light bands gives rise to cross- striations in the cardiac muscle fibres and indicate regular and alternate arrangements of thin and thick filaments in the fibre. Sarcomeres are also present. Cardiac muscle cell frequently branches to form junctions with neighbouring cells. Where two cardiac muscle cells meet end to end, dense zig-zig junction is

 

formed between them. It is called an Intercalated Disc. Long refractory period is present in cardiac muscles.

Nerve Tissue

 

Ordinary connective tissue is absent inside the central nervous system, the neurons are held together by supportive cells called Neuroglia Cells. Nerve tissue is made of neurons and neuroglia cells.

 

A Neuron has a large cell body with two or more, thin protoplasmic processes extending from it. One of the prosses called the Axon is long and conducts nerve impulses away from the cell body. It ends in a number of small branches on muscle fibres, gland cells or other neurons. The remaining one or more prosses conduct nerve impulses towards the cell body and are called Dendrites or Dendrons. The axon terminals may form inter-communicating junctions called Synapses, with dendrites terminals, cell bodies or even axons of other neurons. Nerve impulses pass between neurons through the synapse with the help of chemicals such as acetycholine which are termed Neurotransmitters.

 

The cell body of a neuron is called the Soma. The soma has various shapes. Both the soma and the prosses are covered by the plasma membrane. The soma contains abundant granular cytoplasm and a large nucleus. To serve the high energy needs for impulse conduction, neurons have many mitochondria. Light microscopy shows many small conical, angular or rhomboidal and highly basophilic structures in the cytoplasm of soma and dendrites, They are called Nissl Bodies and are absent in the axon and the axon hiloock. Nissl’s bodies are made up of ribosomes, ER, m-RNA.

 

The processes which are arise from neuron are called as neurites. These are of two types-Dendrites, Axon.

 

1. Dendrites conduct the nerve impulse towards the nerve cell body and are called as afferent processes.

 

1. Axon is a single, usually long process. The part of cyton from where the axon arises is called as axon hillock. The cell membrane of the axon is called axolemma and its cytoplasm is known as axoplasm. The axon divides to form axon ending; each with a synaptic knob. The synaptic knob contain mitochondria and secretory vesicles. The vesicles contain neurotransmitter which is nor-adrenaline or Acetyl chlorine.

 

 

sensory neurone

relay neurone

motor neurone

 

 

 

Practice Test Paper

 

1. Pseudostratified columnar ciliated epithelium is found in

(a) Mouth (b) Stomach / Oesophagus (c) Kidney (d) Trachea

2. Cells lining the blood capillaries are called

(a) Oxyntic cells (b) Endothelial cells (c) Parietal cells (d) Haemocytes

3. The epithelium found in the lining layer of stomach and intestine is [AIEEE 2003]

(a) Columnar (b) Squamous (c) Stratified (d) Pseudostratified

4. Blood vessels are internally lined by

(a) Ciliated epithelium (b) Columnar epithelium (c) Squamous epithelium (d) Striated epithelium

5. Average life span of human B.C. is [ CPMT 2003]

(a) 100 days (b) 90 days (c) 120 days (d) None of these

 

6. B.C. in adult are formed [ 2003]

(a) In the red bone marrow of long bones (b) In the spleen

(c) In the thymus (d) In the liver

 

 

7. The major protein of the connective tissues is [ AIIMS 2001]

(a) Keratin (b) Collagen (c) Melanin (d) Myosin

 

8. Histiocyte is a connective tissue cell, the function of which is

(a) Phagocytic (b) Secretion (c) Fibre production (d) None of these

 

9. Cells which secrete the bone matrix are

(a) Osteoblast cells (b) Osteoclast cells

(c) Bone cells (d) Bone cells and osteoclast cells

 

10. Which of the following cells is phagocytic in nature

(a) Mast cells (b) Podocytes (c) Macrophages (d) Fibroblast cells

 

11. Processes from osteoblasts are called

(a) Dendrites (b) Lamellae (c) Canaliculi (d) Haversian canals

 

12. Which of the following work as phagocytes [AFMC 2003]

(a) WBCs (b) RBCs (c) Enzymes (d) Hormones

 

13. B- and T- cells required for immune system are produced in

(a) Bone marrow (b) Liver (c) Spleen (d) Lymph nodes

 

14. The mast cells secrete the following substance

(a) Heparin (b) Histamine (c) Serotonin (d) All of these

 

15. Phagocytic cells of liver are called

 

(a) Kupffer cells (b) Deiter cells (c) Hensen cells (d) Aciner cells

 

16. Sarcolemma is the covering of

(a) Nerve fibres (b) Muscle fibres (c) Bone marrow (d) Liver, kidney and stomach

 

17. Who propounded the “ Sliding filament theory” for muscles contraction

(a) Cori (b) H.E. Huxley

(c) A.F. Huxley (d) H.E. Huxley and A.F. Huxley

 

18. Nerve fibre is different from the muscle fibre due to the presence of

(a) Myofibrils (b) Lines (c) Sarcolemma (d) Dendrites

 

19. Schwann cells and Node of Ranvier are found in

(a) Nervous tissue (b) Osteoblast (c) Chondrioblast (d) Gland cells

 

20. The junction between Schwann cells is known as

(a) Plasmalemma (b) Node of Ranvier (c) Dendrons (d) Synapse

 

21. Two system which exerts opposite influence on the same organs are

(a) Endocrine and exocrine gland systems (b) Muscular and nervous system

(c) Endocrine and nervous system (d) Sympathetic and parasympathetic systems