Chapter 11 Body Fluids and Circulation by TEACHING CARE online tuition and coaching classes

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Introduction : This system is concerned with the circulation of body fluids to distribute various substances to various body parts.

Functions of Circulatory System.

Transport of various substances such as nutrients, waste products, respiratory gases, metabolic intermediates (Such as lactic acid from muscle to liver), vitamins hormones
Regulation of body pH by means of buffer, body temperature homeostasis, water balance
Prevention of disease by means of antibodies and
Support or turgidity to certain organs like penis and

Types of Circulation.

Circulatory system in various groups of animals can be classified as follows :

Intracellular circulation : Occurs inside the individual cells where the distribution of substances is through cyclosis of cell Example – Protozoans.
Extracellular circulation : When the distribution of the substances occurs inside the body through extracellular or intracellular This is of following types –

Extra organismic circulation : When the water of the external environment circulate through body. This is also called as water circulation system. Example – canal system in porifera, water vascular system in Echinoderms and gastrovascular system in coelenterates.
Intra-organismic circulation : It involves circulation of body It is of following types :
- Parenchymal circulation : In platyhelminthes, the fluid filled spaces present in the mesodermal parenchyma tissue between body wall and internal organs are used in the distribution of
- Coelomic circulation : Coelomic fluid is concerned with the transport of Example – pseudocoelomic fluid in the roundworms and haemolymph in Arthropods.
- Blood vascular system : It contains blood and a pumping structure (heart) for circulation of materials inside the It is of following types –
Open circulatory system
Closed circulatory system

Differences between open and closed circulatory system

Open circulatory system	Closed circulatory system
(1) In open circulatory system blood flows through large open spaces and channels called lacunae and sinuses among the tissues.	(1) In closed circulatory system blood flows through a closed system of chambers called heart and blood vessels.
(2) Tissues are in direct contact with the blood.	(2) Blood does not come in direct contact with tissue.
(3) Blood flow is very slow and blood has very low pressure.	(3) Blood flow is quite rapid and blood has a high pressure.

(4) Exchange of gases and nutrients takes place directly between blood and tissues.	(4) Nutrients and gases pass through the capillary wall to the tissue fluid from where they are passed on to the tissues.
(5) Less efficient as volume of blood flowing through a tissue cannot be controlled as blood flows out in open space.	(5) More efficient as volume of blood can be regulated by the contraction and relaxation of the smooth muscles of the blood vessels.
(6) Open circulatory system is found in higher invertebrates like most arthropods such as prawn, insects, etc., and in some molluscs.	(6) closed circulatory system is found in echinoderms, some molluscs, annelids and all vertebrates.
(7) Respiratory pigment, if present, is dissolved in plasma; RBCs are not present.	(7) Respiratory pigment is present and may be dissolved in plasma but is usually held in RBCs.

Circulatory system in multicellular animals

In protozoans : Distribution of nutrients takes place by cyclosis (streaming movement) of
In poriferans : The vascular system of poriferans is the canal system. A simplest canal system involves ostia (mouth), spongocoel and on osculum (Anus).

Route followed by water current in sponges :

Outside through

Dermal ostia

Incurrent canals

through prosopyles

Radial canals

through apopyles

through

Osculum

Spongocoel

through

gastric ostia

Excurrent canals

In coelenterates : Hydra has a single large internal cavity called coelenteron or gastrovascular cavity. It has single opening the It also extends into the hollow tentacles. It lacks a mesodermal epithelial covering (peritoneum) and a coelomic fluid. It is concerned with first extracellular and then intracellular digestion of food.
In platyhelminthes : Vascular system is absent but circulation occurs with the help of parenchyma hence called parenchymal circulation. Example – Fasciola
In annelids : Vascular system in annelids is a closed circulatory or blood vascular system which comprises four parts : blood, blood glands, blood vessels and hearts.
Blood : Red, due to respiratory pigment haemoglobin dissolved in The blood cells are colourless and nucleated like the leucocytes of vertebrates.
Blood glands : Reddish bodies present on alimentary canal in segments 4, 5 and 6 and are thought to produce blood corpuscles and
Blood vessels : Lack endothelium. The arrangement of blood vessels in first 13 segments is different from that is rest of the body. I^st 13 segments have five longitudinal vessels – dorsal, ventral, a pair of lateral oesophageal and a supraoesophageal Behind 13^th segment has 3 longitudinal vessels – dorsal, ventral and subneural.
Hearts : Four pairs, one pair in each of 7^th, 9^th, 12^th and 13^th Two anterior pairs receiving blood from dorsal vessel only are called lateral hearts and two posterior pairs receiving blood from dorsal vessel as well as

supra oesophageal vessel are called latero-oesophageal hearts. All hearts possess muscular pulsafile walls to pump blood into ventral vessel. Valves present to prevent back flow of blood.

Anterior loops : 2 pairs, one pair in each of the 10^th and 11^th segment, carry blood from lateral oesophageal vessel to supra oesophageal
Lymph glands : Two, small, whitish, located on each side of the dorsal blood vessel in each of the segments 26 and those behind They produce phagocytic cells which are occasionally liberated into the coelomic fluid to phagocytise harmful bacteria and other invaders.

Circulation in earthworm :

Behind 13^th segment

Subneural vessel (from body wall)

I^st 13 segments Dorsal vessel

Lateral hearts

Lateral oesophageals

Anterior loops Supra oesophageal

Ventral vessel : Distributing vessel. Subneural vessel : Collecting vessel. Lateral oesophageal : Collecting vessel. Supra oesophageal : Collecting vessel.

Ventral vessel

Latero oesophageal hearts

Dorsal vessel : Distributing in 1^st 13 segments and collecting in the region behind 13^th segment.

In arthropoda : Blood vascular system in arthropods is ‘Open type’ or “Lacunar type”.

Prawn : Blood vascular system of prawn includes pericardium, heart, arteries, blood lacunar/sinuses, blood channels and Blood is colourless with phagocytic leucocytes and respiratory pigment haemocyanin dissolved in plasma. The blood has remarkable clotting properties. Heart is a muscular, triangular organ without auricle and ventricle but with ostia for inflow of blood into heart and arteries. Five of the arteries arise from the anterior end and one from the posterior end of heart. The prawn’s heart always contains oxygenated blood only and hence, also called as Arterial heart.

Circulation of blood in prawn :

Pumping of oxgenated blood by heart into arteries

Arteries open into blood sinuses and lacunae of haemocoel

Heart collects the oxygenated blood through a slit-like opening in its cardiac wall

Exchange of nutrients, gases and excretory wastes between blood in lacunae and sinuses and surrounding tissues

Oxygenated blood from gills returns to pericardial sinus

Cockroach : Cockroach has an open circulatory system. The body cavity is called

Oxygenation of blood in gills

CHAMBERS OF HEART

VALVES

DORSAL

DIAPHRAGM

Deoxygenated blood seeps out into ventral sinuses to be carried to the gills

OSTIA

ALARAY MUSCLES

ANTENNA

haemocoel filled with a fluid haemolymph. The heart lies in the pericardial sinus of haemocoel. The heart is 13 chambered, tubular dorsal vessel, pulsatile with an anterior aorta.

PERICARDIAL SINUS

VENTRAL DIAPHRAGM

PERIVISCERAL SINUS(HAEMOCOEL) PERINEURAL

SINUS

NERVE CORD

HEAD

NECK

PULSATORY AMPULLA

Each chamber is inverted funnel, shaped provided with valved

Fig. – Blood vascular system of cockroach (Diagrammatic)

lateral apertures called ostia. The heart is supported by 13 pairs of triangular fan like alary muscles. The blood sinuses are dorsal pericardial sinus, middle perivisceral sinus and the ventral perinural sinus or sternal sinus. These sinuses are separated from each other by dorsal diaphragm and ventral diaphragm. Blood or haemolymph is colourless contains haemcytes but is without respiratory pigment as it plays no role in respiration.

Circulation of blood in cockroach :

Heart Aorta Head sinuses

Pericardial sinus

Perivisceral sinus

Perineural sinus

In echinoderms : A true blood vascular system is absent. It is represented by a haemal system which is enclosed within a perihaemal system. haemal system includes oral haemal ring (a sinus), radical haemal sinuses or strands (present in the arms), axial glands, heart, brown glands (present within axial sinus of perihaemal system) and aboral haemal ring, from which arise, five pairs of genital haemal

Important Tips

Blood circulation in vertebrates : Blood circulation was discovered by William harvey. In case of vertebrates, blood circulation is of closed type, which can be grouped into two categories :

(a) Single circulation (b) Double circulation

Differences between single and double circulation

Single circulation	Double circulation
(1) Blood flows only once through the heart in a complete	(1) Blood flows in two circuit pulmonary and systemic. Right auricle Left auricle Lungs Tissues Right ventricle Left ventricle
cycle. Auricle Ventricle
Tissues Gills
(2) Heart pumps only deoxygenated blood, hence called	(2) Heart pumps both deoxygenated and oxygenated
Venous Heart.	blood to lungs and body respectively, hence called
	arteriovenous heart.
(3) Blood is oxygenated in gills.	(3) Blood is oxygenated in lungs.
(4) Less efficient as gill capillaries slow down the blood flow. So, the body receives blood at a low pressure which decreases the rate of O₂ supply to the cells i.e. keeps the metabolic rate low.	(4) More efficient as blood flows at higher pressure, especially in birds and mammals, which increases the rate of food and O₂ supply to the cell and also rapid removal of wastes from them i.e. provides a higher metabolic rate.
(5) Found only in fishes.	(5) Found in amphibians, reptiles, birds and mammals.

Double circulation in mammals can be divided into three parts :

Cardiac circulation : The amount of blood present in the Its value is 7%.
Pulmonary or lesser circulation : The amount of blood present in the surrounding of lungs and pulmonary blood vessels. Its value is 9%.
Systemic or greater circulation : The amount of blood which circulates in the rest part of the Its value is 84%. It can be divided into three parts –

Arterial circulation – 15%

Capillary circulation – 5% Venous circulation – 64%

SUPERIOR VENA CAVA

SYSTEMIC CIRCULATIO

PULMONARY CIRCULATION –

AORTA

HEART –

ARTERIES –13%

INFERIOR VENA CAVA

ARTTERIOLES AND

CAPILLARIES –7%

Heart : The form, structure and function of heart exhibits much variation. The characteristics of heart of fishes, amphibians, reptiles,

VEINS, VENULES AND VENOUS SINUSOIDES –64%

Fig. – Distribution of blood volume in different parts of circulatory system

birds and mammals is presented in the following table.

Heart of vertebrates

Class of vertebrates	Characteristics	Example	Diagram
(1) Pisces (= Branchial	Thick, muscular, made of cardiac muscles, has	Labeo	CONUS ARTERIOSUS VENTRICLE AURICLE SINUS VENO SUS *Fig. – Bronchial heart of a fish* *ex. Labeo and scoliodon*
heart)	two chambers (i) auricle and (ii) ventricle. The	Scoliodon
	heart is called venous heart since it pumps deoxygenated blood to gills for oxygenation.	Neoceratodus
	This blood goes directly from gills to visceral
	organs (single circuit circulation). A sinus
	venosus and conus arteriosus is present. Lung
	fishes have 2 auricles and 1 ventricle.
(2) Amphibians	Heart consists of	Frog	LEFT AURICLE RIGHT AURICLE VENTRICLE *Fig. – Amphibian heart*
	(a) Two auricles	Toad
	(b) Undivided ventricle
	(c) Sinus venosus
	(d) Truncus arteriosus
	(conus + proximal part of aorta) Right auricle
	receives blood from all the visceral organs
	(deoxygenated) via precaval and post caval.
	Pulmonary artery carries deoxygenated blood
	to lungs for oxygenation. This blood returns to
	left auricle via pulmonary vein (Double circuit
	circulation)
(3) Reptiles	Heart consists of : (a) Left and right auricle (b) Incompletely divided ventricle (Ventricle in crocodiles gavialis and alligator is completely divided) (c) Sinus venosus (d) Conus arteriosus divided into right systemic, left systemic and pulmonary arch.	Lizards Snakes Turtles	*Fig. – Reptilian heart*
(4) Aves	Exhibit double circulation Heart consists of (a) Left and right auricle (b) Left and right ventricle (c) Complete separation of arterial and venous circulation (d) Only right systemic arch is present (e) Sinus venosus and truncus arterisious absent	Pigeon	PULMONARY ARCH
			LEFT AURICLE
			RIGHT
			AURICLE
			RIGHT LEFT
			VENTRICLE VENTRICLE
			*Fig. – Pigeon heart*


(5) Mammals	Same as bird except that mammals have left systemic arch.	Rabbit, man

Important Tips

Heart.

Shape and position : Reddish, roughly conical, highly muscular, mesodermal hollow organ of the size of one’s first. Its average weight in males is about 300 gm. and in females about 250 gm. It lies behind the sternum in the mediastinum space of thoracic cavity in between the two lungs. The broader base faces upward and backward. The narrower apex is directed downward, forward and slightly towards left, lying between 5^th and 6^th ribs and rests on the
Protective covering : Heart is enclosed in a tough, 2 layered fibroserous sac, the pericardium. The outer layer is non-distensible fibrous pericardium and inner layer is thin serous pericardium which further consists of outer parietal layer (attached to fibrous pericardium) and inner visceral layer (adhered to the heart).

Outer fibrous pericardium

Pericardium

Inner serous pericardium

Outer parietal layer Inner visceral layer

Between the parietal and visceral layers, occurs a

narrow potential space, the pericardial cavity which is derived from coelom and is filled with serous pericardial fluid for frictionless movement and protection from shock and mechanical injury.

Histology : The heart wall consists of connective tissue, blood vessels and cardiac muscle fibres in 3 different layers – Epicardium, Myocardium and

Endocardium : Innermost layer lining the cavity of heart and consisting of endothelium of squamous cells resting on thin basement membrane of loose connective

DIAPHRAG

Fig. – Diagram to show the layers of the pericardium

Myocardium : Middle, highly vascular layer, composed of cardiac muscle fibres joined together by intercalated disc. The connective tissue in myocardium acts as cardiac skeleton. Endocardium is thickest where the myocarduim is thinnest and vice-versa.
Epicardium : Visceral pericardium, joined to myocardium by connective

BRACHIOCEPHALIC TRUNK

RIGHT BRACHIOCEPHALIC VEIN

RIGHT SUBCLAVIAN ARTERY AND VEIN

SUPERIOR VENA CAVA

RIGHT LUNG

RIGHT ATRIUM

TRACHEA

LEFT COMMON CAROTID ARTERY

LEFT INTERNAL JUGLAR VEIN

LEFT BRACHIOCEPHALIC VEIN

ARCH OF AORTA

PULMONARY TRUNK LEFT PULMONARY

ARTERY

LEFT ATRIUM LEFT LUNG

LEFT VENTRICLE

DIAPHRAGM

PERICARDIUM

CORONARY SULCUS

RIGHT

APEX

INTERVENTRICLAR SULCUS

VENTRICLE

Fig. – Position of heart in our chest cavity

External structure : Human heart is 4- chambered and is divided by septa into two halves

right and left. Each half has one darker, thin walled auricle in the broader upper region and one lighter, thick-walled ventricle in the narrower lower
Auricles (Atria) : Two in , demarcated externally from ventricles by irregular groove called coronary sulcus and from each other by interatrial sulcus. When atria contract, small curtain like flaps called auricular appendages or appendices project from sides of auricles and overhang the corresponding ventricles.
Ventricles : Two in demarcated externally from each other by an oblique groove called

BRACHIOCEPHALIC TRUNK

SUPERIOR VENA CAVA

ASCENDING AORTA

RIGHT PULMONARY VEINS

RIGHT ATRIUM

CORONARY SULCUS

RIGHT VENTRICLE

INTERVENTRICULAR SULCUS

LEFT COMMON CAROTID ARTERY

LEFT SUBCLAVIAN ARTERY

ARCH OF AORTA PULMONARY

TRUNK

LEFT PULMONARY VEINS

LEFT ATRIUM GREAT

CARDIAC VEIN

LEFT VENTRICLE

APEX

interventricular sulcus which contains coronary blood vessels. The right ventricle does not reach apex.

Fig. – External features of human heart

Sinus venosus and conus arteriosus : Sinus venosus and conus/truncus/bulbus arteriosus are accessory chambers in the heart of lower vertebrates (fishes and amphibians). In rabbit, sinus venosus is formed in the embryo but later it becomes a part of wall of right

In frog, sinus venosus spreads upon most of the dorsal side of heart and conus arteriosus lies obliquely upon the ventral surface of right atrium.

LEFT ANTERIOR VENA CAVA

AOROTIC TRUNKS

RIGHT ANTERIOR VENA CAVA

RIGHT ATRIUM

SINUS VENOSUS PULMONARY VEINS

VENTRICLE

AORTIC TRUNKS

LEFT ANTERIOR VENA CAVA

LEFT ATRIUM

CORONARY SULCUS

POSTERIOR

CONUS ARTERIOSUS

CORONARY SULCUS

DORSAL VIEW VENTRAL VIEW

Fig. – Dorsal and ventral of frog’s heart

(v) Internal structure

(a) Auricles : Atria are thin walled. They act as

SYNANGIUM

TO CAROTID

reserviors for blood entering the heart. Right auricle is bigger than left auricle and both are separated by a myomembranous partition called Interatrial or interauricular septum. During embryonic stage, at the place of this septum, there are present septum primum and septum secondum having a gap (aperture) called foramen ovalis between them. From the opening of inferior vena cava upto foramen ovalis, there is a flap called Eustachian flap which prevents the blood in the foetal heart go to lungs because in foetal life, lungs are not functional purification of blood is done by placenta.

At the time of birth, there is closure of foramen ovalis but there remains depression on posterior part

TO PULMONARY ARCH

CONUS ARTERIOSUS

SPIRAL VALVE PLANGIUM

POCKET VALVE COLUMNAE

CARNAE

VENTRICLE

ARCH CAROTID ARCH SYSTEMIC ARCH PULMONARY ARCH

ANTERIOR VENA CAVA

PULMONARY VEIN APPERTURE

SINU-ATRIAL APERTURE LEFT AURICLE

INTERATRIAL SEPTUM ATRIO-VENTRICULAR APERTUBE

VENTRAL FLAP OF ATRIO-VENTRICULAR VALVE

PERICARDIAL CAVITY CHORDAE TENDINAE

PERICARDIAL MEMBRANE

POCKETS OF VENTRICULAR CAVITY POSTERIOR

VENA CAVA

of the right surface of interauricular septum in rabbit. In man this depression is present on both the side.

Fig. – Horizontal longitudinal section (H.L.S.) of frog’s heart (ventral view)

because of least regenerative power in human being. The depression towards right atrium is called fossa ovalis and depression towards left atrium is called fossa lunata.

PFO (Patient Foramen Ovalis) or septal defect : In case there is no closure of foramen ovalis, then disease is called PFO. In this condition, there is mixing of blood after birth which gives bluish appearance to the body called as Cyanosis. Such child is called Blue Baby.

The inner surface of auricles is smooth. A network of muscular ridges called musculi pectinati or trabeculi pectinati occurs internally in the region of the auricular appendages and give comb like appearance.

(ii) Ventricles : The right and left

ventricles are demarcated by an interventricular septum which is obliquely curved towards right, so that the left ventricle is larger than right one. However, the cavity of left ventricle is relatively smaller and nearly circular because the myocardium of left ventricleis 3 times thicker than right ventricle whose cavity is larger and somewhat crescentic.

The walls of the ventricles are internally raised into a number of thick, muscular, column shaped projections called columnae carnae or trabecular carnae; and a few large muscular elevations called papillary muscles or musculli papillares

PULMONARY ARTERY

SUPERIOR VENA CAVA

BRANCHES OF RIGHT PULMONARY ARTERY

TO LUNG

FROM LUNG BRANCHES OF RIGHT

PULMONARY VEIN

RIGHT ATRIUM CORONARY SINUS

FOSSA OVALIS

TRICUSPID VALVE

CHORDAE TENDINAE RIGHT VENTRICLE

INFERIOR VENA CAVA

PULMONARY SEMILUNAR VALVE

AORTIC ARCH

LIGAMENTUM ARTERIOSUM TO LUNG

BRANCHES OF LEFT PULMONARY ARTERY

BRANCHES OF LEFT PULMONARY VEIN

LEFT ATRIUM FROM LUNG

AORTIC SEMILUNAR

VALVE

MITRAL VALVE INTERVETNRICULAR

SEPTUM

LEFT VENTRICLE MYCARDIUM

DESCENDING AORTA

which are 3 in right ventricle and 2 in left ventricle. These muscles act as anchors for chordae tendinae.

PAPILLARY MUSCLE

Fig. – Internal anatomy of human heart

Chordae tendinae : Numerous, strong, inelastic thread like tendons present in the mammalian heart but absent in frog. One end of these threads is attached to the cusps of A.V. valves and the other end to the papillary muscles of the ventricles. These muscles contract during ventricular systole and pull the valves downwards, thus, preventing their everting into atria. The chordae tendinae hold the valves in place.

Regurgitation : If there is weeakening of papillary muscles or breaking of chordae tendinae, then AV valves revert into auricles. So, blood goes in opposite direction, it is called regurgitation. Sometimes, there is narrowing of valves. So, there remains gap between the valves which causes regurgitation.

Moderator band : Right ventricle contains a prominent muscular trabeculum called moderator band which extends from the interventricular septum to anterior papillary muscle.

(vi) Major blood vessels associated with heart : The blood vessels that enter or leave the heart are called Great Blood Vessels.

Superior vena cava or precaval : Brings deoxygenated blood from head and upper parts of the body into the right auricle through an opening which is single in human and cat and two in rabbit as there are 2 precavals
right and left in In frog, right and left precavals open into sinus venosus.
Inferior vena cava or post caval : Drains deoxygenated blood from middle and lower parts of the body into the right auricle through a single opening which is bordered by a membranous, falciform fold which is a remnant of the foetal valve of Eustachian. In frog, post caval opens into sinus
Coronary sinus : Returns deoxygenated blood from heart wall into right auricle through a single
Pulmonary vein : Four pulmonary veins, two from each lung, carry oxygenated blood from the lungs and open into the left auricle through four In rabbit, the pulmonary veins open in the left auricle through 2 openings.
Pulmonary aorta/arch : Arises from upper left corner of right ventricle through a single opening and divides into right and left pulmonary arteries which carry deoxygenated blood to the lungs for
Systemic aorta : Arises from upper right corner of left ventricle through a single opening and has 3 regions – ascending aorta, arch of aorta and descending It distributes oxygenated blood to various body parts except lungs.

Ligamentum arteriosus : During foetal life, because the lungs are non-functional hence blood of pulmonary aorta comes into systemic aorta through a small duct called ductus botalli or ductus arteriosus soon after birth, deposition of elastin fibre blocks this duct, forming a new structure called ligamentum botalli or ligamentum arteriosus.

PDA (Patient Ductus Arteriosus) : If the ligamentum arteriosus remains open, the condition is called PDA. In this case, there is mixing of blood which leads to blue baby.

Valves : The valves present in the mammalian heart are tendinous cords.

Eustachian valve : Present on the opening of inferior vena cava (post caval) in the right auricle in rabbit, whereas in human, the vestige of eustachian valve is present over the opening of post caval It allows the passage of blood in right auricle.
Haversian valve : Present in human but absent in It is present over the opening of precaval vein and allows the passage of blood in right auricle.
Thebesian or coronary valve : Present over the opening of coronary sinus in right auricle in mammals and allows the passage of blood in right
Atrio-ventricular valves : Auricles open into the respective ventricles through wide passages called

auriculo ventricular apertures or A.V. apertures which are guarded by one-way A.V. valves or parachute valves and are located dorsally or posteriorly. There are 2 types of valves in mammals.

Right V. valve or Tricuspid valve : Present between right auricle and right ventricle. It consists of 3 membranous flaps or cusps.
Left V. valve or Bicuspid or Mitral valve : Present between left auricle and left ventricle. It consists of 2 flaps or cusps. The bicuspid valve resembles mitre or topi of bishop,

hence, also called as Mitral valve.

SUPERIOR VENA CAVA

AORTA

PULMONARY VALVE

RIGHT ATRIUM

TRICUSPID VALVE

INFERIOR VENA CAVA

DEOXYGENATED BLOOD OXYGENATED BLOOD

PULMONARY ARTERY

PULMONARY VEINS

LEFT ATRIUM MITRAL VALVE

AORTIC VALVE LEFT

VENTRICLE

RIGHT VENTRICLE

Fig. – Path of blood through the heart

The upper edges of the flaps are attached to the margins of the A.V. apertures while the lower edges project freely into the ventricles. The free edges of these flaps are connected by chordae tendinae to he papillary muscles of the ventricles. These valves allow the passage of blood from auricles into ventricles but prevent backflow.

In frog, the A.V. valves are semilunar type and not of cuspid type. There is single row of A.V. valves due to single ventricle.

Semilunar valves : At the base of pulmonary arch and systemic aorta, three membranous, pocket-shaped flaps called semilunar valves are present which are set in a ring with their cavities directed away from the ventricles. They allow the passage of blood from ventricles to respective blood vessels, but prevent the return of

Sinus of valsalva : When the semilunar valves open towards aorta, there remains gap between the flaps and the wall of aorta. This gap is called sinus of valsalva. When ventricles relax, blood is filled in this sinus and is called Drooping of blood.

Corpora Arantii : Thick nodules present on the edges of the flaps of semilunar valves which prevent the reverting of these valves into the ventricles.

(viii) Physiology of heart : The heart pumps blood to all parts of the body. The deoxygenated blood is drained into right auricle through superior and inferior venae cavae and coronary sinus whereas the pulmonary veins carry oxygenated blood from lungs to the left auricle. This is called as Auricular circulation. About 70% of the auricular blood passes into the ventricles during diastole. This phase is called diastasis. The rest of 30% of blood passes into the ventricles due to auricular systole (contraction). In this way, blood reaches the ventricles and is called ventricular filling. During ventricular systole (which starts first in left ventricle than in right ventricle), the pressure increases in the ventricles, thus, forcing the oxygenated blood from left ventricle into systemic aorta and deoxygenated blood from right ventricle into pulmonary aorta. The systemic arch distributes the oxygenated blood to all the body parts except lungs while pulmonary aorta carries the deoxygenated blood to lungs for oxygenation.

During foetal life, heart receives and pumps mixed blood and hence, it can be compared with transitional heart, the eustachian flap, in the foetus directs the blood of right atrium towards left atrium through foramen ovalis. From left atrium, blood reaches left ventricle from which the systemic aorta arise. An iliac artery arise from this aorta from the internal branches of illiac artery, two umbilical arteries arise which come out of body through naval and reach placenta where exchange of gases takes place. A single umbilical vein arises from placenta and enters the foetal body through naval and reaches the liver to give some blood to it and some blood to inferior vena cava. Inferior vena cava already possess impure blood. So, there is mixing of blood. In foetus, pure blood is there only in umbilical vein (allantoic vein). Umbilical cord is a tube possessing a jelly like connective tissue (Wharton jelly) along with two umbilical arteries and one umbilical vein.

Heart beat : The spontaneous and rhythmic contraction and relaxation of the heart to pump out and receive blood to and from the body is called Heart beat. Depending upon the nature of control of the heart beat, hearts are of 2 types –

Neurogenic and Myogenic or autorhythmic.

Differences between Neurogenic heart and Myogenic heart

Neurogenic heart	Myogenic heart
(1) The heart beat is initiated by a ganglion situated near	(1) The heart beat is initiated by a patch of modified heart

the heart.	muscle.
(2) The impulse of contraction originates from nervous system.	(2) The impulse of contraction originates itself in the heart.
(3) The heart normally stops beating immediately after removal from the body. Therefore, heart transplantation is not possible.	(3) The heart removed from the body continues to beat for some time. Therefore, heart transplantation is possible.
(4) Examples : Hearts of some annelids and most arthropods.	(4) Examples : Hearts of molluscs and vertebrates.

Origin and conduction of heart beat : Initiation of heart beat is under special bundles of cardiac muscles called nodal tissue. The cardiac muscles have less actin and So, structurally they become more a nerve than muscle and functionally they are similar to neurons.
- Morphology of nodal tissue : The nodal tissue consists of the following –
  - Sinu-auricular or A. node : Also called as pacemaker, node of keith and flack, heart of heart, brain of heart, pulsation centre. It is located in the right wall

of right atrium below the opening of superior vena

cava. This is the place where sinus venosus is incorporated in the wall of right atrium in the embryo. S.A. node is the main tissue of heart and has highest degree of autrohythmicity (generates beating impulse at the rate of 70-80 times/minute) but least conductivity. The rhythmic impulses produced are called as Sinus rhythmia. In frog S.A. node is present in sinus venosus.

Atrio-ventricular node or V. node : Also called reserve pacemaker, node of Twara and Aschoff. Discovered by Lewis Kent. It lies in the right atrium near the junction of interauricular and interventricular septum close to the opening of

SINU-AURICULAR NODE

RIGHT ATRIUM

INTERNODAL PATHWAY

RIGHT BUNDLE OF PURKINJE FIBRES

RIGHT VENTRICLE

LEFT ATRIUM

AURICULO VENTRICULAR NODE

BUNDLE OF HIS

INTERVENTRICULAR SEPTUM

LEFT VENTRICLE

LEFT BUNDLE OF PURKINJE FIBRES

coronary sinus. It is concerned with the conduction of

Fig. – Conducting system of rabbit’s heart (ventral view)

cardiac impulses generated by S.A. node, but it can also generate the impulse at the rate of 40-60/minute. These impulses produced are rhythmic and called nodal rhythmia. In frog, A.V. node is absent.

Bundle of His or V. bundle : Discovered by His. It arises from A.V. node, descends in the interventricular septum and bifurcates into two branches innervating the wall of right and left ventricle respectively. The myocardium of atria and ventricles are discontinuous and this bundle is the only muscular connection between the two. It is concerned

RIGHT VAGUS PARASYMPATHETIC

SINUATRIAL NODE

LEFT VAGUS (PARASYMPATHETIC)

SYMPATHETIC GANGILA

AURICULO VENTRICULAR NODE

ACCELERATOR NERVES

with the conduction of impulse from atria to the tip of

Fig. – Innervation of human heart by autonomic nerves

ventricle but can also generate impulse at the rate of 35-40/minute. The impulses produced are non-rhythmic.

Purkinje fibres : Numerous, modified muscle fibres which act as sympathetic nerve They arise from branches of bundle of His and provide impulse to myocardium of ventricles. They can also generate non- rhythmic impulse at a rate of 30-35/minute.

Working of nodal tissue : A. node spontaneously initiates a wave of contraction which is conducted along the tracts of special muscle fibres called internal pathways over both the auricles at a rate of 1m/sec. The impulse generated travels first in the right atrium than in left atrium. So, right atrium contracts first but the contraction ends simultaneously in both atria. As the musculatures of atria and ventricles are discontinuous and are separated by a septum of fibrous connective tissue, called annular pad in mammals, the wave of contraction is received by A.V. node from myocardium of atria and is provided to bundle of His. The impulses reach the A.V. node about 0.03 seconds after their origin from S.A. node. The A.V. node generates a fresh wave of contraction which passes over both the ventricles along the bundle of His and its ramifications at the rate of 1.5 to 4 m/sec. The Purkinje fibres bring about the contraction of ventricles from the apex of heart which passes quickly towards the origin of pulmonary and systemic arches forcing blood into them.

S.A. node not only acts as pacemaker but also establishes the basic rhythm at which the heart beats. In case of degeneration of S.A. node, A.V. node can generate impulse but it will lead to abnormal beating (arrhythmia). The failure of atrial impulse to pass into ventricles for a few seconds to few hours is called ventricular escape or stokes- adams syndrome leading to delayed pick up of heart beat. In such conditions, artificial pacemaker (Lithium Battery) is placed underneath the patient’s chest.

Ectopic pacemaker : If any cardiac muscle other than the conducting tissue (nodes) generates impulse, then extra beats are heard. Such muscles are called Ectopic pacemaker.

In mammals, conducting system of the heart has S.A. node, A.V node and complicated system of conducting fibres. But in frog, it has only S.A. node and system of conducting fibres is simple.

Heart beat rate : Heart beat/minute or number of cardiac cycles/minute. Example – frog-64/min., rabbit- 200/min., human-70-80/min. Females have higher heart rate than males.

Normal heart beat rate ® Rhythmia Abnormal heart rate ® Arrhythmia Decrease in heart rate ® Bradycardia Increase in heart rate ® Tachycardia

Regulation of heart beat : The centre controlling the heart rate (cardiac centre) is present in medulla oblongata of brain and possess chemoreceptors sensitive for CO₂, O₂ and also for blood pressure. This centre is under the influence of hypothalamus which is the controller of autonomic
- Nervous control : Brain receives two sets of nerve fibres : Sympathetic and para sympathetic or

When there is increase in blood CO₂, the sympathetic nerve fibres stimulate S.A. node by producing sympathin (adrenaline + noradrenaline). This compound induces impulse generation by inducing entry of

Ca²⁺ into cardiac muscles. So, heart beat and force of contraction increase (Tachycardia). After action, sympathin is destroyed by sympathenase, COMT (catechol orthomethyl transferase) and MAD (Mono Amino Oxidase).

When there is increase in blood O₂, the parasympathetic or vagal (10^th cranial) nerve inhibits S.A. node by producing acetylcholine. This compound increases contraction time and hence, heart beat is decreased (Bradycardia). After action, acetyl choline is destroyed by enzyme acetyl choline esterase (AchE). This chemical regulation of heart beat on behalf of nerves was discovered by Otto Loewi.

Vagus escape : Stimulation of vagus nerve decreases the heart rate but its continuous stimulation shows no further decrease. This phenomenon is called Vagus escape.

Hormonal control : Hormones from adrenal medulla adrenaline and nor adrenaline accelerate the heart beat, the latter under normal conditions and the former at the time of

Pounding : Very fast heart beat during some conditions like anger and love. Thyroxine hormone also increases the heart beat by increasing energy production.

(d) Factors affecting heart rate

Heart rate increases with increase in basal metabolic rate (BMR).
Heart increases as the size of the animals body
Decrease in pH also increases heart
Heart rate increases with increase in
Increase in Na⁺ ions in blood or in cardiac muscles, increase heart
Increase in Ca²⁺ ions in blood increase heart beat but if they are injected in cardiac muscles, heart stops in contracted phase which is called Systolic Arrest.
Injection of K⁺ ions in heart muscles stop impulse So, heart stops in diastolic or Relax phase.
H⁺ ions reduce force of contraction of
Increased inspiration, muscular exercise, low oxygen tension, injection of adrenaline, thyroxine, sympathin

– all increase heart rate.

Increased expiration, during sleep, injection of acetylcholine decrease heart
Stenosis – Narrowing of valve is called

Cradiac cycle

A regular sequence of three events :

Auricular systole (0.1 sec)
Ventricular systole (0.3 sec)
Joint Diastole or complete cardiac diastole (0.4 sec)

During the completion of one heart beat is called as cardiac cycle. These events are repeated in a cyclic manner during each heart beat.

Auricular systole : The atria contract due to wave of contraction stimulated by A. node contraction of auricles drives most of their blood into respective ventricles as the A.V. valves are open. There is no backflow of blood into the large veins as the contraction begins at the upper end and passes towards ventricles and moreover, the valves present at the opening of these veins close. Also, blood is already present in large veins which offers resistance to the blood that may return from the atria. At the end of a atrial systole, there starts the relaxation of auricles (auricular diastole) and contraction of ventricles (ventricular systole) simultaneously. Atrial systole takes 0.1 second while atrial diastole is of about 0.7 seconds.
Ventricular systole : The ventricles begin to contract due to a wave of contraction stimulated by A.V. Due to ventricular systole, the pressure of blood in ventricles immediately rises above that in the auricles. With this pressure, the bicuspid and tricuspid valves close rapidly to prevent the backflow of blood. This closure of A.V. valves at the start of ventricular systole produces first heart sound called “Lubb” or Systolic sound. The semilunar valves are also close at this time. When the pressure of blood in the ventricles exceeds that in the great arteries, the semilunar valves open and blood enters into the great arteries. This marks the end of ventricular systole which takes about 0.3 seconds. Now the ventricles start relaxing (ventricular diastole which lasts for about 0.5 sec.)
Joint diastole : The ventricles and auricles are in the diastolic phase As the ventricular diastole progresses, the pressure in the ventricles falls below that in the great arteries. So, to prevent backflow of blood from great arteries into ventricles, the semilunar valves close rapidly. This rapid closure of semilunar valves at the beginning of ventricular diastole produces second heart sound “Dup” or diastolic sound.

During joint diastole, blood from great veins and coronary sinus flows into the atria and some blood also passes from auricles into the respective relaxing ventricles due to less pressure in ventricles. This phase takes only 0.4 seconds and is also called as blood receiving period of heart. Thus a cardiac cycle is completed in 0.8 seconds.

Cardiac output : Volume of blood pumped from heart (left ventricle) into the systemic aorta in one minute is called cardiac output. It is also called minute volume. It is calculated as the product of stroke volume (amount of blood pumped by left ventricle each time it contracts) and rate of heart beat.

i.e. Cardiac output = Stroke volume ´ Rate of heart beat

= 70 ml ´ 75 times/minute = 5040 ml/minute ≃ 5 litres/minute

Total amount of blood in human body is about 6.8 litres (7% of body weight). During mild exercise, the cardiac output rises to about 11 litres. Cardiac output is directly proportional to the size of the organism, metabolic rate etc. but is inversely proportional to age.

Fractions of cardiac output : Amount of pure blood going to an organ per minute is called as fraction of the
- Cardiac fraction – 200 ml/
- Hepatic fraction – 1500 ml/ (28% of blood as liver is the busiest organ of body and has maximum power of regeneration).
- Renal fraction – 1300 ml/min (25% of blood)

Myofraction – 600-900 ml/min.
Cephalic organs – 700-800 ml/
Remaining organs – Remaining

Cardiac index : Cardiac output per square metre of body surface area per minute. As area of normal young adult is 7 metre square, so, cardiac index is 3 litres/min/square metre.
Cardiac reserve : Maximum amount of blood that can be pumped by left ventricle under the conditions of maximum needs. In this condition, heart beat can go upto 250 and stroke volume can go upto 100 ml per Cardiac reserve is 25-30 litres which is about 5-6 times of cardiac output.
End diastolic volume : Amount of blood present in left ventricle at the end of diastole. It is the maximum volume of the cavity of left ventricle and is equal to 120-130 ml.
End systolic volume : Amount of blood present in left ventricle at the end of systole. It is the least volume of the cavity of left ventricle and is equal to 50-60 ml.
Stroke volume : (70 ml) is equal to the difference between the end diastolic volume and end systolic
Venous return : Amount of impure blood returning to righ atrium per minute is called venous return and is equal to 25 litres. The venous return is due to many factors –
Little blood pressure in the veins.
Skeletal muscle pump : Veins usually pass through skeletal muscles which, on contraction, exert milking action on So, there is upward movement of blood.
Respiratory pump : Due to the movement of diaphragm during breathing, blood moves upward in the
Pressure difference in venae cavae and right The negative pressure created in right atrium due to the atrial diastole results in sucking up of blood from venae cavae into the atrium.

Heart sounds

In normal heart, four sounds are heard. First and second sounds have audible frequencies, so, they can be heard very easily. 3^rd and 4^th sounds are having very less frequency (less than 20 Hertz). So, they can’t be heard easily. Third heart sound is running water sound. Fourth heart sound is also called Atrial sound as it appears when blood flows from atria into ventricles due to atrial contraction.

Differences between first and seconds heart sounds

First heart sound (Lubb)	Second heart sound (Dup)
(1) It is produced by closure of bicuspid and tricuspid valves at the start of ventricular systole.	(1) It is produced by closure of semilunar valves at the start of ventricular diastole.
(2) It is low pitched, less loud and of long duration.	(2) It is higher pitched, louder, sharper and of short duration.
(3) It lasts for 0.15 seconds.	(3) It lasts for 0.1 second.
(4) Its principal frequencies are 25 to 45 cycles per second.	(4) Its principal frequency is 50 cycles per second.

Heart sounds can be heard by an instrument called stethoscope by placing its receiver on left side of the chest at the fourth intercostal space. Hearing of sound with the help of stethoscope is called Auscultation. The quality of heart sounds indicates the state of the heart valves. Defective or damaged heart valves lead to the backflow of blood either from ventricles to auricles or from aortae to ventricles. Such defects are detectable as abnormal hissing sound called “Murmur”.. Defective valves may be replaced or repaired surgically. Syphilis and Rheumatic fever cause Murmur. The instrument used to magnify and record the heart sound is called Phonocardiogram.

Electrocardiogram (ECG)

A graphic record of electrical events occuring during a cardiac cycle is called Electrocardiogram. The instrument used for rcording the heart’s electrical variations is called Electrocardiograph in which the potential differences of heart muscles are recorded by a galvanometer. In ECG, there are 2 types of waves :

Depolarisation waves : They represent the generation of the potential These waves appear only when both electrodes of galvanometer are in different fields. When both the electrodes are in same field, there is no deflection and wave drops down to base line.
Repolarisation waves : They appear when depolarisation is over and the muscle fibre is returning to its original polarity. When both electrodes are in same polarity (means 100% repolarisation and 100% depolarisation), there is no

A normal ECG has 5 deflection waves – P, Q, R, S and T. Out of them – P, R and T waves are above the base line and are called positive waves. The Q and S waves are below base line and are called negative waves. The port of the base line between any 2 deflections is called Interval.

T (sec)

0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0

R R R R

P T P T P T P T

Q Q Q Q

S S S S R

– 1

Fig. – Normal electrocardiogram

P wave : Indicates impulse of contraction generated by S.A. node and its spread in atria causing atrial depolarisation. The interval PQ represents atrial contraction and takes 0.1 second.

QRS complex : Indicates spread of impulse of contraction from

node to the wall of ventricles through bundle of His and pukinje fibres causing ventricular This complex also represents repolarization of S.A. node.

The RS of QRS wave and ST interval show ventricular contraction (0.3 seconds). QRS is related to ventricular systole.

T wave : Indicates repolarisation during ventricular relaxation.

P T

Q S

ATRIAL DEPOLARISATION VENTRICULAR DEPOLARISATION

VENTRICULAR REPOLARISATION

Fig. – Normal ECG deflections, Depolarisation and repolarisation

Any abnormality in the working of heart alters the wave pattern of ECG. Thus, ECG is of great diagnostic value in cardiac diseases. ECG also indicates the rate of heart beat.

If S.A. node is degenerated, the P wave disappears. This condition is called Heart fail. Atrial repolarisation wave is not seen in normal ECG because at this time, the depolarisation wave of ventricles is being recorded. When there is degeneration of bundle of His, the P to R interval increases. This is called Wenckebach phenomenon.

If bundle of His is completely cut, the P-R interval becomes infinite as the bundle of His is to transmit the cardiac impulses. It is called total heart fail or total heart block. In arborisation heart block, the defect lies in purkinje fibres. In heart attack, T waves become negative. When there is decrease in blood supply to a part of heart, there occurs death of myocardium. This condition is called Myocardial infarction (MI). It is acute heart attack. The ST part of ECG is depressed when heart muscles receive insufficient oxygen and is elevated in acute MI. When there is degeneration of myocardium and deposition of fibres, the condition is called fibrillation during which, ECG obtained is bizzare or non-decipherable.

Vector cardiogram : Represents the direction of transmission of impulse.

History of ECG : The ECG was first recorded by Waller in frog. First human ECG was prepared by Einthoven who also discovered the electrocardiograph and discussed the principles of ECG. Hence, he is commonly called “Father of Electrocardiography”.

Blood vessels

The study of blood vessels is called Angiology. The blood vessels are of following types :

Arteries (ii) Capillaries (iii) Veins

Vasa vasorum : Supply blood to the wall of large blood vessels.

Arteries : Thick walled, carrying oxygenated blood (deoxygenated in pulmonary artery) from heart to various parts of body. These blood vessels are grouped as Aorta which branches to form arteries which further divides into thinner branches called arterioles inside the organ. Average diameter of arteriole is 120 mm. the arterioles further divide into smaller vessels called meta-arterioles (70 mm) which divide into capillaries. At the beginning of capillary, the arterioles posses circular muscles called precapillary sphincter which regulates flow of blood into the capillaries which is called vasomotion.

Muscleless end of meta-arteriole is called thoroughfare channel or preferential channel. The largest artery is dorsal / abdominal aorta (systemic aorta).

Elastic or conducting arteries receive blood from heart and do not provide it to any organ rather they provide blood to other atreries and are pressure reservoirs of blood.

Muscular arteries show vasoconstriction and vasodilation and provide blood to the organs.

Anastomosis : If more than one arteries are supplying to one organ then branches of these arteries unite to form a network called Anastomosis. It provides many collateral or alternate pathways of blood supply. So, if there is blocking of any artery, it will not lead to necrosis.

End arteries : In organs like heart, branches of different arteries do not unite rather they terminate due to which the alternate pathways are not available. In such cases, blocking of any artery leads to necrosis of related part of organ. To develop alternate pathway in such conditions is called as By pass surgery.

Capillaries : Smallest blood vessels, discovered by Marcello Malpighl (also layered nucleated squamous epithelial cells called endothelium resting on a basement Diameter of capillary is about 8m. These are

also called as exchange vessels as they are the site of exchange of material between blood and tissue because of least barrier in them. The capillaries can be grouped into two categories :

Arteriolar capillary : Which supplies nutrition, respiratory gases to the body cells.
Veinular capillaries : Which collect the metabolic wastes from the body

Capillaries possess abour 5% of total body blood and are present near almost all cells of body in the intercellular spaces. The tissues which are devoid of intercellular spaces are also devoid of capillary. They are called avascular tissues.

Capillaries are surrounded by cells of connective tissue called pericapillary cells. Some of these cells are contractile and phagocytic in nature and are called Rouget cells or pericytes.

Continuous capillaries are without fenestra/aperture, hence are less permeable. These are present in organs such as lungs, muscles, connective tissues and brain tissues.

Fenestrated capillaries possess apertures/fenestra and are found in those organs where there is maximum need of permeability such as endocrine glands, intestinal villi, cavities of brain, kidney, ciliary body of eye.

Sinusoids are irregularly dilated capillaries found in organs where there is decrease in flow rate such as liver, spleen, bone marrow, parathyroid, pituitary gland. In liver, sinusoids are branches of venules and open into venules while in other organs, they originate from arteriole and unite to form venules.

Veins : These are thin walled, carrying deoxygenated blood (oxygenated in pulmonary vein) from tissues to the heart. Venules, smallest branches, unite to form veins which in turn unite to form vena cava. The largest vein is inferior vena cava/post caval. Varicose veins is stout, blood filled painful veins specially of the limbs due to defective watch pocket

(a) Histology of arteries and veins :

ENDOTHELIUM

DIRECTION OF BLOOD FLOW

CAPILLARY

VEIN ARTERY

VEINS (A)

Fig. – (A) Venous valves, (B-D) Histology of the blood vessels

Tunica externa or tunica adventitia : Outermost, fibrous, made up of collagen rich connective tissue and less elastin The collagen fibres give strength to the blood vessels and prevent their overdilation.

Tunica media : Middle, thickest, made up of smooth involuntary muscle fibres and elastin fibres. This layer is very much variable because number of elastin fibres and muscle fibres depend upon the position of blood vessels from the
Tunica interna or tunica intima : Innermost, thinnest, made up of inner, single layer of simple squamous epithelial cells called endothelium resting on a basement membrane and outer layer of elastic (yellow fibrous) connective The hollow space in the blood vessel is called lumen.

Differences between arteries and veins

S.No.	Characters	Arteries	Veins
(1)	Wall	Thick, more elastic, non collapsible.	Thin, less ealstic, collapsible.
(2)	Tunica externa	Less developed, so less strong.	More developed, so more strong.
(3)	Tunica media	More muscular and has many elastic fibres.	Less muscular and only a few elastic fibres.
(4)	Tunica interna	Endothelial cells more elongated. Elastic membrane more developed.	Endothelial cells less flat. Elastic membrane less developed.
(5)	Lumen	Narrow	Wider
(6)	Position	Deep seated except wrist, neck etc.	Superficial
(7)	Valves	Without valves.	With valves to prevent back flow.
(8)	Direction of blood flow	From heart to body organs	From body organs to heart
(9)	Nature of blood	Oxygenated except pulmonary artery.	Deoxygenated except pulmonary vein
(10)	Blood pressure	More, generally 120/80 mm of Hg.	Less, generally 0 mm of Hg.
(11)	Speed of blood	Fast	Slow
(12)	After death	Becomes empty	Contain blood
(13)	Amount of blood	15% at any given time.	64% at any given time
(14)	Colour	Pink	Dark red
(15)	Disintensibility	Less	More

Blood pressure : The pressure exerted by the blood on the wall of the blood vessels in which it is present is called blood pressure. It is usually measured in brachial artery by an instrument called sphygmomanometer (invented by Riva-Rocci). Arterial blood pressure is of 2 types :
- Systolic blood pressure : It is the pressure exerted by blood on the walls of the blood vessels due to the systole of ventricles and is equal to 120 mm Hg. During ventricular systole, there is expansion in the artery due to the uncoiling of elastic Hence, the pressure is maximum in arteries but gradually decreases in capillaries and veins.
- Diastolic blood pressure : It is the pressure exerted on walls of blood vessels when the ventricles are During ventricular diastole, the uncoiled elastic layer recoils leading to normalization of artery. Hence, blood pressure drops down to 80 mm Hg. Thus, blood pressure in normal person is systolic/diastolic pressure i.e. 120/80 mm Hg.
- Pulse pressure : The difference between systolic and diastolic pressures is called pulse pressure and its normal value is 120 – 80 mm Hg = 40 mm Hg. It provides information about the condition of
- Mean arterial pressure : It is the average pressure of systolic and diastolic pressures. As the blood remains in the systolic phase for shorter period and in the diastolic phase for longer period, the mean pressure of blood lies near the diastolic

This value varies at different levels of circulation being maximum (100 mm Hg) in the aorta and minimum (0

mm Hg) in the venae cavae under normal conditions.

Pulse : It is the pressure wave of distension and recoiling felt in the radial artery due to the contraction of left ventricle which force about 70-90 ml of blood in each cardiac cycle to aorta. This perssure wave of contraction travels down to the wall to the arteries and is called the pulse.

The pulse is measured in the radial artery in the wrist but can be felt in the temporal artery over the temporal bone or the dorsal pedis artery at the bind of ankle. The pulse normally travels at the rate of 5-8 m/second.

Since each heart beat generates one pulse in the arteries so the pulse rate per minute indicates the rate of heart beat. So the normal pulse rate in a normal adult person is 72/minute.

The normal ratio of systolic pressure to diastolic pressure to pulse pressure is about 3 : 2 : 1.

Important Tips

(c) Factors affecting blood pressure :

Age : With the advancing age, BP increases after the age of 60 years, it is calculated as 100 + age of the
Cardiac output : BP increases with the increase in cardiac
Elasticity of blood vessels : BP is inversely related to the elasticity of the blood
Total peripheral resistance : Constriction of the blood vessels increases BP whereas dilation of the blood vessels decreases

Hypotension : Low blood pressure with systolic below 110 mm Hg and diastolic below 70 mm Hg. It is caused by low metabolic rate, starvation, anaemia, chronic vasodilation of arterioles, lower pumping activity of heart, loss of blood in haemorrhage, valvular defects, nervous disorders and Addison’s disease. It may cause fainting.

Hypertension : Persistent high blood pressure with systolic more than 140 mm Hg and diastolic more than 90 mm Hg. It is caused by decrease in extensibility of the artery due to atherosclerosis and arteriosclerosis. Sclerosis means hardening and narrowing of blood vessels which may be due to the deposition of cholesterol or calcium or lipid or any other compound in the wall of the arteries and arterioles.

In atherosclerosis deposition is mainly in tunica interna of the blood vessels which prevents their dilation. The atherosclerosis is, infact, the beginning of thickening and hardening of blood vessels but later, the deposition of cholesterol and other compounds takes places in both tunica media and tunica interna leading to arteriosclerosis.

Hypertension caused by hormones (epinephrine, aldosterone, renin) is called secondary hypertension, other forms of hypertension are known as primary or essential hypertension.

A blood pressure of 220/120 mm Hg may cause internal haemorrhage due to rupturing of some blood vessels. Cerebral haemorrhage due to rupturing of some blood vessels cerebral haemorrhage or complete cessation or great

decrease in blood supply to some part of brain causes stroke or CVA (Cerebrovascular accident). Hypertension is commonly called as silent killer.

High density lipoproteins (HDL) are responsible for excretion of cholesterol and thus, reduce the risk of coronary heart diseases. Low density lipoproteins (LDL) and very low density lipoproteins (VLDL) cause deposition of cholesterol in the wall of the arteries and thus, increase the risk of coronary heart diseases. The blood pressure was first measured by Stephen Halls in horse. Highest blood pressure is recorded in giraffe.

Types of blood circulation in human

The physiology of blood circulation was first described by Sir William Harvey in 1628. The blood circulation in our body is divisible into 3 circuits –

Coronary circulation : It involves blood supply to the heart wall and also drainage of the heart

Coronary arteries : One pair, arising from the aortic arch just above the semilunar valves. They break up into capillaries to supply oxygenated blood to the heart wall.

Coronary veins : Numerous, collecting deoxygenated blood from the heart wall and drains it into right auricle through coronary sinus which is formed by joining of most of the coronary veins. But some very fine coronary veins, called venae cordis minimae open directly in the right auricle by small sized openings called foramina of Thebesius.

Pulmonary circulation : It includes circulation between heart and lungs. The right ventricle pumps deoxygenated blood into a single, thick vessel called pulmonary aorta which ascends upward and outside heart gets divided into longer, right and shorter, left pulmonary arteries running to the respective lungs where oxygenation of blood takes The oxygenated blood from lungs is returned to the left auricle by four pulmonary veins. Left auricle pumps this blood into the left ventricle.

Systemic circulation : In this, circulation of blood occurs between heart and body organs. The left ventricle pumps the oxygenated blood into systemic arch which supplies it to the body organs other than lungs through a number of arteries. The deoxygenated blood from these organs is returned to the right auricle through two large veins (precaval and post caval). Right auricle pumps this blood into the right Thus, the sytemic circulation involves two circuits

–

Arterial circulation or Arterial system
Venous circulation or Venous system

Time taken by blood to circulate in the body from heart to heart to heart is called circulation time. The amount of blood flowing per minute in pulmonary and systemic circulation is same.

(a) Arterial system : It involves aorta, arteries, arterioles and meta- arterioles. It supplies oxygenated blood to all parts of the body except lungs.

The left ventricle of the heart pumps the oxygenated blood into a single, question marked shaped, long vessel called left carotid-systemic aorta. It is the largest blood vessel of the body. The initial part of systemic aorta is dilated and is called aortic sinus. It

EXTERNAL CAROTID INTERNAL CAROTID

VERTEBRAL

RIGHT COMMON CAROTID RIGHT SUBCLAVIAN BRANCHIOEPHALIC

AORTA AXILLARY

HEART

BRACHIAL

SUPERIOR MESENTRIC

RIGHT RENAL

LUMBAR COMMON

ILIAC

EXTERNAL ILIAC

POSTERIOR TIBIAL

LEFT COMMON CAROTID

LEFT SUBCLAVIAN

PULMONARY ARTERIES PULMONARY TRUNK

CORONARY ARTERY INFERIOR PHRENIC

COELIAC LEFT RENAL

GENITAL

INFERIOR MESENTERIC

ULNAR RADIAL

INTERNAL ILIAC

FEMORAL DEEP FEMORAL

POPLITEAL

ANTERIOR TIBIAL

Fig. – Arterial system in human body

possess some baroreceptors and some CO₂ sensitive cells. Barroreceptors are supplied with 9^th cranial nerve (glossopharyngeal).

After ascending from the heart, the systemic aotra turns and descends down to the level of lower border of fourth lumbar vertebra. At its distal extremity, it bifurcates into right and left common iliac arteries. The sytemic aorta has following parts –

Ascending aorta : It gives off left and right coronary

Arch of aorta : It gives – Innominate or Brachiocephalic artery left common carotid artery left subclavian artery.

Descending aorta : The aorta turns towards the back of heart and finally converts into dorsal aorta. While dorsal aorta is in thorax, it is called thoracic aorta; when it goes down into diaphragm, it is called abdominal aorta. Mammals have left systemic arch while birds have right systemic

Arterial System

Ascending

artery

Descending

artery

Right side Left side Thoracic region Abdominal region

Verte

Inferior phrenic

Coelic artery

Superior mesenteric

Renal

Lumbar

Sacral

Inferior mesenteric

Common iliac

Left

gastric

Common Splenic

hepatic

iliac

Pancreoduodenal Jejunal Iliac Iliocolic Internal

External iliac

(1) Ascending aorta

From convexity of the arch of aorta

Brachiocephalic (innominate) : Unpaired, largest branch of the aorta divides into right subclavian towards right side and right common carotid towards left side. Right subclavian gives off vertebral artery (supplies to head and part of right shoulder) and then enters into right arm, now called axillary artery or brachial artery, which divides into ulnar and radial arteries in the region of elbow. The right common carotid, enters into head and divides into external and internal carotids which supply the right parts of head by their
Left common carotid : Unpaired artery, enters into head and divides into left external and internal carotids which supply the left parts of the head by their
- The external carotids of both sides provide blood to thyroid gland, tongue, throat, face, ear,
- The internal carotids of both sides supply to brain, eye, inner part of nose and These internal carotids go upward and enter skull through foramen magnum and unite at the base of brain along with the vertebral

arteries of both sides. So, there is formation of a ring shaped artery called as “Circle of willis”. From this circle, many branches or arteries arise which go to different parts of brain.

In frog, the internal carotid has at its base, carotid labyrinth (spongy mass of non-contractile fibro-elastic tissue) which acts as a sensory organ to detect blood pressure in artery.

Left subclavian artery : Unpaired artery, it gives off a left vertebral artery (supplies to head and part of left shoulder) and then enters into left arm, now called left axillary artery or left brachial artery which divides into ulnar and radial arteries in the region of

Descending aorta : The descending dorsal aorta divided into thoracic and abdominal
- From thoracic segment of aorta : Several pairs of small arteries arise in this region to supply various parts such as pericardium (pericardial artery); lungs and bronchi (bronchial artery); oesophagus (oesophageal artery); mediastinal organs and thymus (mediastinal artery); intercostal muscles and mammary glands (intercostals and subcostal arteries); upper surface of diaphragm (superior phrenic artery).
- From abdominal region of aorta : In the abdominal region, abdominal aorta gives off several pairs of Some of the major ones are as follows
Inferior phrenic artery : Right and left to supply the lower surface of the
Coeliac artery : Unpaired, divides into three branches
- Left gastric artery : To
- Common hepatic artery : To pylorus, pancreas, gall bladder, liver, cystic duct, hepatic ducts
- Splenic artery : To pancreas, stomach and spleen.
Superior mesenteric : Unpaired, supplies various parts of small intestine (except superior part of duodenum part of colon and caecum). Its sub branches are
- Pancreo duodenal artery : To pancreas and
- Jejunal artery : To
- Ilial artery : To ileum and
- Iliocolic artery : To ileum and colon.
Supra renal artery : Supplies the adrenal
Renal arteries : One pair, supply to
Lumbar arteries : 4 pairs, supply the skin, muscles, joints, vertebrae, meninges, spinal cord in the lumbar region.
Sacral artery : Supplies the tissues of sacral
Inferior mesenteric artery : Unpaired, supplies most part of colon, rectum and anal
Common iliac arteries : Two, right and left, formed by bifurcation of aorta at its lower end. Each common iliac artery divides into external and internal iliac arteries. The internal iliac (hypogastric) artery supplies

lies viscera and wall of pelvic region, perineum and gluteal regions. The external iliac artery enters into the leg now called femoral artery continues down the thigh, now called popliteal artery which bifurcates into anterior and posterior tibial arteries, at about the level of knee.

Inguinal canal : Connects abdominal cavity with the cavity of scrotum. So, through this canal, spermatic artery (testicular artery), subclavian vein and sperm duct pass.

(b) Venous system : It originates in tissues by union of capillaries and ends in the atrium of heart. It includes two major veins – superior and inferior vena cava which drain the deoxygenated blood into the right atrium.

Venous System

Superior vena cava Inferior vena cava Pulmonary vein

Branchiocephalic

vein

Inter jugular

vein

Subclavian

vein

External jugular

vein

Azygous &

Hemi azygous vein

Internal

thoracic vein

Inferior

thoracic vein

Left superior

intercostal

Cephalic

vein

Axillary

vein

Common	Lumbar vein	Genital vein	Renal vein	Supra renal	Inferior	Hepatic vein
iliac vein				vein	phrenic

External

iliac

Internal

iliac

tibial

Posterior

tibial

Popliteal Large

saphenous

Small saphenous

Superior vena cava (pre caval) : Single, formed by the union of right and left brachiocephalic (innominate) veins. It collects blood from head, neck, arms and chest It involves the following veins –
Brachiocephalic veins : Two, each is formed by the union of an outer subclavian vein and medial internal jugular Each vein also receives blood from different thoracic parts of its sides through three main veins.
Internal thoracic vein : From some muscles and mammary
Inferior thyroid vein : From thyroid
Left superior intercostal vein : From upper part of
Internal jugular vein : Two, right and left. Each one is formed by the union of numerous sinuses and veins of the cranial cavity, superior part of the face and some part of neck and collects blood from these
Subclavian veins : Two, right and left, formed in the shoulder region by union of cephalic and axillary veins of respective
Axillary veins : Two, right and left, present in the respective arms and collect blood from these

Cephalic veins : Two, right and left, collect blood from respective arms and shoulder
External jugular veins : Two, right and left, open into respective subclavian vein. They collect the blood from parotid gland, facial muscles and superficial parts of
Azygos and hemiazygos veins : Azygos vein originates in lumbar region towards right side of mediastinum and ascends upwards small veins from lumbar and thoracic parts of backbone, oesophagus, mediastinum, pericardium empty into it.

Towards the left side of the body originates hemiazygos and accessory hemiazygos collects blood from oesophagus, mediastinum, intercostal muscles, mammary glands etc. and drains into Azygos which in turn opens into superior vena cava. Accessory hemiazygos drains blood into left innominate vein.

Inferior vena cava : It is the largest vein, originated in inferior lumbar region by the union of right and left common iliac veins and opens into right atrium by separate opening. It collects blood from all body structures below the diaphragm. It involves following veins –
- Common iliac veins : Two, right and Each one is formed by union of external and internal iliac veins.
- External iliac vein : This is the continuation of femoral vein which collects blood from leg. Femoral vein in turn is formed by the union of anterior tibial vein, posterior tibial vein, popliteal vein, large saphenous vein, small saphenous vein, etc. which collect blood from different parts of leg. External iliac vein also collects blood from pubic region and parts of pelvis through number of small Last saphenous vein is the

longest vein of the body.

RIGHT EXTERNAL JUGULAR

RIGHT INTERNAL JUGULAR

RIGHT SUBCLAVIAN

BRACHIOEPHALIC

SUPERIOR VENA CAVA

HEART HEPATIC

HEPATIC PORTAL RIGHT SUPRARENAL

RIGHT RENAL RIGHT TESTICULAR

LUMBAR

COMMON ILIAC

EXTERNAL ILIAC FEMORAL

GREAT SAPHENOUS

LEFT EXTERNAL JUGULAR

LEFT EXTERNAL JUGLAR

LEFT SUBCLAVIAN

LEFT AXILLARY

CORONARY

INFERIOR PHRENIC

LEFT CEPHALIC LIVER

INFERIOR VENA CAVA

LEFT SUPRARENAL

LEFT RENAL

LEFT TESTICULAR

INTERNAL ILIAC

FEMORAL POPLITEAL

POSTERIOR TIBIAL

ANTERIOR TIBIAL

(iii) Internal iliac (Hypogastric)

Fig. – Venous system in male human being

veins : Two, right and left. Each one is formed by union of number of small veins, which collect blood from pelvis, pelvic viscera, pelvic girdle, sacrum, rectum, ureter, urinary bladder, uterus, vagina, prostate glands, seminal vesicle, penis, scrotum etc. (i.e. number of reproductive organs).

Lumbar veins : Four pairs, which collect blood from muscles, skin and vertebrae of lumbar region and drains it into inferior vena cava.
Genital veins : In man, right testicular vein collects blood from male organs and inguinal regions and drains it into inferior vena cava. Left testicular vein drains the blood into left renal vein. In woman, the right ovarian vein drain blood from ovaries, uterus and empties into inferior vena cava. The left ovarian vein opens into left renal vein.
Renal veins : Two, right and left collects blood from respective kidneys and opens into inferior vena The left renal vein is about three times longer than the right one.
Suprarenal vein : Two, right and left, collects blood from adrenal glands. Right one opens into inferior vena cava whereas left one opens into left renal
Inferior phrenic veins : These veins drain the blood from lower surface of diaphragm. The right one ends in post caval. The left one is often doubled with its one branch ending in left renal or suprarenal vein and the other in post
Hepatic veins : They drain blood from liver into the post Urea is maximum in hepatic vein while it is minimum in renal vein.

Portal system

It is a part of venous circulation which is present between two groups of capillaries i.e. starts in capillaries and ends in capillaries. The vein which drains blood into organs other than heart is called portal vein.

Types of portal system : It is of following types :

Hypothalamo-hypophysial portal system
Hepatic portal system
Renal portal system

(i) Hypothalamo-hypophysial portal system :

Present in higher vertebrates (amphibia, reptiles,

birds and mammals). Blood from hypothalamus is collected by hypophysial portal vein which ends in anterior lobe of pituitary gland. The superior hypophysial artery which bring blood into circle of willis bifurcate outside the lobe; one branch supplies the lobe itself, but the other one supplies the hypothalamus. The vein that drain the blood from hypothalamus then runs into pars distalis and divide into capillaries. Thus this is a portal vein called hypothalamo-hypophysial portal vein.

INFUNDIBULUM

NEUROHYPOPHYSIS

(POSTERIOR LOBE)

VEIN

OPTIC CHIASMA

HYPOTHALAMUS

CAPILLARIES ARTERY TO BRAIN

HYPOPHYSIAL PORTAL VEIN

ARTERY TO ADENCHYPOPHYSIS

ADENCHYPOPHYSIS

(ANTERIOR LOBE)

SECONDARY CAPILLARY PLEXUS

Function : This portal system enables the

releasing factors and inhibiting factors from

Fig. – Human hypophysial portal system

hypothalamus to reach upto anterior pituitary.

Hepatic portal system : Found in all In mammals, there is a single vein called hepatic portal vein, formed by the union of four main veins, which drain venous blood from different parts of alimentary canal (digestive system) into the liver. These veins are :
Posterior mesenteric vein : Collect blood from rectal wall and anal This vein possess maximum diluted blood. Posterior mesenteric made up of by joining of 4 small veins that is rectal vein, sigmoid vein, left colonic vein and it opens into the splenic vein.
Anterior mesenteric vein : Collect blood from wall of colon, caecum and small intestine. This vein possesses largest concentration of nutrients (glucose, amino-acid and vitamins). This vein formed by the joining of right colonic vein, ileocolic vein and appendicular vein.
Splenic vein : Collect blood from spleen and pancreas splenic vein possess free haemoglobin in large
Right gastric vein : Receives blood from stomach and

Posterior mesenteric vein open into splenic vein and splenic, anterior mesenteric, right gastric fused to form hepatic portal vein, which leads to blood in the liver.

In amphibians (example – frog), hepatic portal system is formed of single hepatic portal vein and single anterior abdominal vein. The latter collects blood from leg region and drains it into the left lobe of liver.

Significance of hepatic portal system : The hepatic portal system has following significance.

The blood which comes from the alimentary canal contains digested food like glucose and amino acids. The excess of glucose is converted into glycogen which is stored in the liver for later When an individual feels deficiency of food, the glycogen is converted into glucose and is transferred to the blood stream via hepatic veins.
Harmful nitrogenous waste like ammonia is converted into urea which is later removed by kidneys. Thus the blood is detoxified (purified) of harmful nitrogenous
Liver produces blood

INFERIOR VENA CAVA

HEPATIC VEIN

LEFT LOBE OF LIVER

HEPATIC PORTAL VEIN

SUPERIOR MESENTRIC VEIN

RIGHT COLONIC VEIN

ILEOCOLIC VEIN

DESCENDING COLON

CAECUM APPENDICULAR VEIN

APPENDIX

RIGHT GASTRIC VEIN

OESOPHAGUS

STOMACH

SPLEEN

SPLEENIC VEIN

PANCREAS DUODENUM

INFERIOR MESENTERIC VEIN

DESCENDING COLON

LEFT COLONIC VEIN

SIGMOID VEIN

SIGMOID COLON

proteins which are put into blood circulation.

RECTAL VEIN RECTUM

Fig. – Human hepatic portal system

Renal portal system : It is well developed in fishes and amphibians it is reduced in reptiles and birds and is absent in This system carries blood from the posterior region of the body to the kidneys by renal portal veins, thence its name. The kidneys remove the waste products from the blood and then the blood is passed to the post caval by renal veins. Why renal portal system is absent in mammals ? The mammals have no renal portal system due to the following facts :
It is an Evolutionary trend that fishes and amphibians have well developed renal portal system, while in reptiles and birds this system gets Finally in mammals it ultimately disappears.
The heart of mammals is four

Due to the four chambered heart in mammals there is total separation of oxygenated and deoxygenated
Posterior portion of body gets oxygenated blood from the heart and after oxidation process, etc. the blood does not get so much impurities that it should go to the kidneys first for filtration as happens in fishes and

Renal portal system in frog consists of one pair of renal portal vein, each one formed by the union of formal vein and sciatic vein. It collects blood from leg region and drains it into kidney. It also collects blood from dorsal part of lumbar region through dorsolumbar vein.

Function : Renal portal system helps in blood filtration by draining it into kidney which filters the blood.

Lymphatic system

It is a part of greater circulation which begins in the tissue fluid with lymphatic capillaries which are always terminally closed. This system terminates into venous system near heart. The main components of this system are :

(i) Lymph (ii) Lymphatic system in frog

(iii) Lymphatic system in human (iv) Lymphatic organ

Lymph : Lymph can be defined as blood minus RBC’s. In addition to the blood vascular system all vertebrate possess a lymphatic It is colourless or yellowish fluid present in the lymph vessels. It is a mobile connective tissue like blood and is formed by the filtration of blood. This process involves the diffusion of substances from blood capillaries into the interstitial space which is, thus, the primary site of lymph formation. Two forces bring about a steady filtration of plasma fluid into the tissue spaces : capillary pressure (30-35 mm Hg) and colloid osmotic pressure in tissue fluid (8 mm Hg). Most of the compounds come out by filtration and few such as glucose come out by diffusion. These compounds get collected in the intercellular space as Tissue fluid or Interstitial fluid which is, infact, a part of blood. So, it must return to blood otherwise blood volume will decrease. For this, the outflux of plasma fluid into capillaries is prevented by colloid osmotic pressure in plasma (28 mm Hg) which counteracts the above two forces. When the blood flows from arteriolar to venous part of the capillaries, the capillary pressure falls to 10-15 mm Hg due to which the blood capillaries absorb waste material and CO₂ from filtered blood. Thus, at the side of veinlets, net diffusion pressure = 28

– 15 = 13 mm Hg. After absorption by veins, a small amount of CO₂ and waste material still remains in the tissue fluid which is absorbed in the lymphatic capillaries as lymph. So, we can say that lymph is modified tissue fluid.

Differences between lymph and blood

S.No.	Characters	Blood	Lymph
(1)	RBC	Present	Absent
(2)	Blood platelets	Present	Absent
(3)	WBC	Persent, generally 7000/cu mm	Persent, generally 500-75000/cu mm
(4)	Plasma	Present	Present
(5)	Albumin : globulin	Albumin > Globulin	Albumin > Globulin
(6)	Fibrinogen	More	Less
(7)	Coagulation property	More	Less
(8)	Direction of flow	Two way, heart to tissues and tissues to heart	One way, tissues to heart
(9)	Rate of flow	Fast	Slow
(10)	Glucose, urea and CO₂	Less	More

Hence, lymph can be represented as :

Lymph = Blood – [RBC + platelets + plasma proteins of high molecular weight]

Composition of lymph : Microscopic examination of lymph depicts that is contains a large number of leucocytes (mostly lymphocytes) ranging from 500 to 75,000 per cubic mm. No blood platelets present. The composition of the non cellular part of lymph (fasting) is as follows :

Water 94% (2) Solids 6%
- Proteins : Protein content is roughly half of the plasma and varies from 2.0 – 4.5%. It varies according to the part of the body from which is collected, e. in liver 6%, in limb 2% of intestinal part 4%. The varieties of proteins are found – albumin, globulin and fibrinogen. In addition to this, traces of prothrombin, fibrinogen.
- Fats : In fasting condition fat content is low but after a fatty diet it may be 5.0 – 15%.
- Carbohydrates : Sugar, 2 mgm per 100 ml.
- Other constituents : Urea, creatinine, chlorides, phosphorus, calcium, enzymes and
Normally the rate of lymph formation is equal to the rate of its return to the blood

Lymphatic system in frog : In frog, all lymph capillaries empty into large, irregular lymph spaces called lymph The latter are lined by a membranous squamous epithelium and occur in all parts of body. The major lymph sinuses are :
Subcutaneous lymph sinuses : These are

FEMORAL SINUS CRURAL SINUS

LATERAL SINUS DORSAL SINUS

several sinuses located beneath skin and separated from each other by thin septa of connective tissue

CONNECTIVE TISSUE SEPTA

SUBMAXILLARY SINUS

(figure). Major subcutaneous sinuses are brachial lymph sinuses in forelimbs, dorsal and lateral trunk

ABDOMINAL SINUS

PECTORAL SINUS

sinuses and pelvic lymph sinuses in posterior part of trunk, and crural or femoral lymph sinuses in hindlimbs.

Fig. – The subcutaneous lymph sinuses

Subvertebral lymph sinus (= cisterna magna) : This is a single large lymph sinus located beneath vertebral column throughout the length of the Kidneys are lodged in this sinus.

A number of lymph capillaries empty into the body cavity or coelem also. This proves that the coelomic fluid is also lymph, and the coelom is a large lymph sinus.

Lymph hearts : Two pairs of small, sac-like structures, one pair located behind the transverse processes of third vertebra, and the other in the region of urostyle, are closely connected with lymph sinuses in frog (figure). These have thin, but muscular walls. by contraction of their walls, these regularly pulsate and pump the lymph of sinuses into veins. Obviously, these are “lymph heart”. The anterior lymph heatrs pump the lymph into subscapular veins and the posterior ones into femoral veins.

(iii) Lymphatic system in human

(a) Lymph capillaries : Small, thin, lined by endothelium resting on a basement membrane and fine whose one end is blind and other end unites to form lymphatic ducts. These are present almost throughout the body but are absent in brain, eyeball, spinal cord, internal ear, bone

1^ST PAIR OF HEARTS

DORSAL SINUS

FEMORAL SINUS

PELVIC SINUS

BRACHIAL SINUS

LATERAL SINUS

2^ND PAIR OF HEARTS

marrow etc. Lymph capillaries in the region of small intestine in villi are

called “lacteals” which collect chyle which is milky white in colour due to absorbed fat. Lacteals help in the absorption of digested fat.

Fig. – Lymph hearts of frog

Lymphatic ducts or vessels : Numerous, present in various parts of body. These vessels are like veins as they have all the three layers – tunica externa, tunica media and tunica interna, and are provided with watch pocket or semilunar valves but valves are more in number than veins.

Flow of lymph in lymphatics : Pulsations of lymph hearts in frog create sufficient force to maintain a steady flow of lymph in the lymphatic In mammals, the credit for maintaining onwards flow of lymph goes to (i) the “squeezing force” created by the muscles of body wall and internal organs, (ii) the breathing movements of diaphragm and thoracic cage, (iii) mild peristalsis created by smooth muscles of the wall, of lymphatics themselves, and (iv) the pressure created by increasing amount of lymph in the lymphatics. Certain compounds like fats increase the rate of lymph flow and are called lymphata gogue. Blocking of lymph

RIGHT THORACIC LYMPH DUCT

RIGHT SUBCLAVIAN VEIN

CERVICAL NODES

LEFT SUBCLAVIAN VEIN

AXILLARY NODES LEFT THORACIC

LYMPH DUCT INTERCOSTAL NODES

CYSTERNA CHYLI

LUMBAR NODES ILIAC NODES

INGUINAL NODES

flow causes oedema.

(d) Types of lymphatic ducts : Two

Fig. – Lymphatic system of mammals shown in man (ventral view)

main types :

Right lymphatic duct : It is the smallest lymphatic duct with the length of approximately 1.25 cm. Its one end is blind and other one opens into right subclavian vein at the junction of right internal jugular vein. It collects lymph from one-fourth of the body (right part of head, neck, thoracic cavity and right arm).
Left lymphatic duct/thoracic duct : It is the longest lymphatic duct with the length of approximately 38-45 cm. It originates from cisterna chyli and empties into left subclavian vein. It collects lymph from three-fourth part of the body e. complete posterior part through cisterna chyli, left part of head, neck, thoracic cavity and left arms.
Cisterna chyli receptaculum chyli : It is a dilated sac like structure present below the diaphragm in lumbar region at the level of second lumbar It collects lymph from posterior part of body i.e. abdomen, pelvic region and hind limbs and drains it in the left lymphatic duct.

It shows inflation and deflation due to the movement of diaphragm which is a passive movement. Hence, it is also called as passive lymphatic artery. It is also called as second heart.

Lymph nodes or lymph glands : These are the masses of lymphatic tissue and connective tissue (reticular tissue) and are located on the capillaries either solitary or in cluster. Where they are present solitary and in few number, such tissues are called diffused lymphatic tissues and where they are in clusters, they are called tonsils.

Lymph nodes are covered by capsule of white collagen tissue. Outer region of lymph node is called cortex and inner region is called medulla. In medulla, there are medullary cords, (cord like arrangement of lymphocytes). Cortex possess follicles (clusters of lymphocytes), outer part of which possess T-cells and macrophages while the inner part possess B-cells.

Lymphadenitis : During infection, central part of follicle shows rapid division and formation of plasma cells. hence, this part is also called reaction centre. The inflammation of lymph nodes in such condition is called Lymphadenitis.

TRABECULUS

MEDULLARY CORDS

AFFERENT LYMPH VESSELS

SUBCAPSULAR SINUS

BLOOD VESSELS

Some of the common lymph nodes are – Axillary nodes (in armpits), genital (Inguinal) nodes (in pubic region), cervical

EFFERENT LYMPH VESSEL

Fig. – Scheme to show some features of the structure of a lymph node

nodes (in neck region), intercostal nodes (in chest region), lumbar nodes (in lumbar region), iliac nodes (in pelvic region) and payer’s patches (in small intestine). Besides these lymphatic nodes, a number of them are also present near major blood vessels (arteries), specially dorsal aorta.

Tonsils : Clusters of lymph nodes. They are very often called as policemen. Various tonsils are – Normal tonsils (in pharynx), adenoid tonsils (in nasopharynx), abdominal tonsils (in vermiform appendix) and policeman of intestine (in lamina propria of ileum). Adenoid tonsils are present upto 7 years of age, then they are degenerated. Their swelling is called adenoid. Inflammation of tonsils is called Tonsilitis.

Haemal lymph node : In many animals some lymph nodes are found to possess red colour, due to the presence of blood in them. In man they are found in the retroperitoneal tissues and also in the mediastinum. In these nodes some of the so-called lymphatic channels contain blood, while the rest of the nodes possesses the same

structure as the typical lymph node. Spleen may be regarded as the modified haemal lymph (haemolymph) node. Lymph nodes are located at intervals along its course.

Function of lymph nodes :

They produce and supply lymphocytes to the blood and as a supportive function the trabeculae carry blood vessels which supply the
They make screening of the lymph by means of phagocytic
They serve a great defensive role against bacterial
They temporarily stop the spread of cancer cells as those cells have to penetrate through the lymph vessels to the lymph nodes from where they spread in the
They act as mechanical filters to resist the entrance of poisonous substances into
They carry out immunological They help in elaboration of antibodies and in the development of immunity.
Lymph nodes produce g-globulin.

(iv) Lymphatic organs : The lymphatic organs present in our body are chiefly spleen (haemolymphatic organ) and thymus (endolymphatic organ).

(a) Spleen : In frog, a small and spherical, dark red organ, called spleen, is found attached, by means of a fold of peritoneum, to the anterior part of large intestine in rabbit, the spleen is some what flattened and elongated, and attached to the hind border of stomach.

Structure of spleen : Spleen is madosermal in origin. Spleen is the largest solid mass of reticulo-endothelial tissue in the body. Histologically it is formed by following structure –

Capsule : It is the outer covering of spleen formed of elastic fibrous connective tissue and smooth The outer layer of the capsule is the serous coat formed of visceral peritoneum.
Trabeculae : Narrow fold like septa or trabeculae extend inwards from the capsule, dividing

MESOTHELIAL CELL LINING RED PULP TRABECULA CAPSULE

CENTRAL ARTERY

VENOUS SINUSES IN RED PULP

GERMINAL CENTRE

(SECONDARY MODULE)

the spleen tissue into several incomplete lobules. These

are better developed in rabbit and other mammals

CORTEX OF WHITE PULP

TRABECULAR

ARTERIOLE IN RED PULP

VEIN IN TRABECULA

than in frog.

Splenic pulp : The reticulo-endothelial

ARTERY SURROUNDED BY

LYMPHOCYTES

Fig. – Histological structure of spleen (Diagrammatic)

tissue is called splenic pulp. It contains a denser network of blood capillaries, small sinuses and fine blood vessels. The meshes of this network are studded with numerous splenic cells, red, blood corpuscles, macrophages and lymphocytes. The splenic pulp is of two distinct types –

(i) White pulp (ii) Red pulp

White pulp : The white pulp is the accumulation of lymphatic tissue surrounding a major arterial vessels of the spleen. This lymphatic tissue is comprised of lymphocytes, plasma cells, macrophages or other free cell lying in the meshwork of reticular fibres at various points along the course of the vessels where the infiltration of lymphocytes is greater, it forms spherical or ovoid nodules which are called as splenic nodules of white The splenic nodules may have typical germinal centres.
Red pulp : It is a modified

ACCORDING TO ‘CLOSED THEORY’ ARTEROLE OPENING DIRECTLY INTO SPLENIC SINUSOIDS

SPLEENIC VENOUS SINUSES

RED PULP

CENTRAL ARTERIOLE CENTRAL ARTERY

TRABECULAR VEIN

TRABECULAR ARTERY

ARTERIAL

CAPILLARY CAPUSLE

MESOTHELIAL CELL LINING

PENICILLAR ARTERY

RED PULP ARTERIOLE

ELLIPSOLD

(SHEATHAL ARTERIOLE) GERMINAL CENTRE

SPLEENIC NODULE TO WHITE PULP

PERI ARTERIAL LYMPH SHEATH OF WHITE PULP

lymphatic tissue and is mostly infiltrated with cells of the circulating blood. It consists of two components –

Splenic sinuses or

ACCORDING TO ‘OPEN THEORY’ ARTEROLE OPENING INTO PULP ON (MESH) BETWEEN SPLENIC SINUSAL

Fig. – Anatomy of circulation in a splenic lobule showing both closed circulation and open circulation (Diagrammatic)

Splenic cords or Billroth cords [big blood sinuses]. It is raddish due to excessive number of RBCs. Red pulp of spleen contains reticular fibres, erythrocytes, lymphocytes, macrophages, monocytes

In mammal embryos the red pulp contains myelocytes, erythroblast and also megakaryocytes. These types of cells are not present in adult spleen except in certain pathological condition.

Function : Although located close to the alimentary canal, the spleen has nothing to do with digestive system. it is, in fact, an important constituent of the reticuloendothelial system of body and performs the following functions:

Its macrophages engulf (= phagocytize) and destroy wornout blood corpuscles, dead and live pathogens, cell debris, pigment granules and other useless particulate materials, thus regularly cleaning the blood of its
It is active haemopoietic organ. In foetal life, the red pulp possess myeloblast, erythroblast and Hence, in foetus, it produces blood. In adults, the red pulp possess macrophages, plasma cells and lymphocytes. So, in adults, it is not producing blood rather it is screening blood.
In adults, it also serves as a sort of “blood bank”. Its sinuses act as “reservoirs of blood”. When required, their blood is squeezed into general circulation. Similarly, RBCs stored in spleen are also released into general circulation when
Many lymphocytes of spleen produce
Spleen also acts as Grayeyard or Slaughter house of worn out
Haemolysin is formed in
Haemoglobin is broken down into haem and globin by spleen. The haem is further split into iron and pigment haematoidin, which becomes bilirubin of plasma. Iron first stored is splenic pulp then transferred into liver and bone After splenectomy this storage function suffers and more iron is lost.

Besides all these functions, the primary function of spleen is that it assists liver and helps in maintaining the composition of blood.

(b) Thymus : It is a bilobed mass of lymphiod tissue which is situated in the upper chest near front side of heart. It is prominent in children but begins to degenerate in the adults. It stimulates the development and differentiation of T-lymphocytes, which produce antibodies, thus, increasing the resistance to infection.

Important Tips

Lymphatic system in class amphibia is of open
Lymph sinuses are the large spaces containing These are present in frog but absent in mammals.
Lymph heart – The heart which collects
In frog, lymph hearts are two pairs – an anterior pair and a posterior pair which collect lymph from respective There are no lymph hearts in mammals.
The process of lymph formation is called
Lymph serves to return the interstitial fluid to the
Oedema (Edema) or Dropsy – A local swelling due to the accumulation of tissue fluid in tissues caused by the defective circulation of blood or
Lymph nodes are secondary lymphatic organs because they harbour Primary lymphoid organs are bone marrow and thymus.
Lymph nodes are maximum in armpits and
Spleen is called “first reservoir” of blood while liver is called “second reservoir” of
Spleen, liver and kidneys – all are called filter apparatus of
Diseasess where there is more destruction of RBCs such as malaria, banti disease, there is enlargement of spleen called as splenomegaly.
Thymus is concerned with the immunological
In AIDS, there occurs generalised swelling of all lymph
Spleen is absent in
Cardiology – Study of
Pericarditis – Inflammation of
Endocarditis – Inflammation of endocardium, generally caused due to the rheumatic
Frank-Starling law – Within certain physiological limits, the heart pumps all the blood that comes in
Largest sized heart is found in Blue whale.
Papillary muscles of ventricles are found only in the heart of
Valves in heart were first reported by Fabricious.
World’s first heart transplant was performed by Christian Barnard on 55-year old Louis Wash kansky in Cape town, South Africa in the year 1967.
India’s first heart transplant was conducted by cardiac surgeon P. Venu Gopal in a 42-year old man Mr. Devi Ram on 3^rd August, 1994 at AIIMS, Delhi.
Cardiomegaly – Enlargement of
Myocardial Ischaemia – Deficient blood supply to heart muscle leading to angina
Angina pectoris – Severe but temporary heart pain of short duration which is usually felt in front of the chest and may pass into the
Coronary thrombosis – Formation of blood clot in coronary arteries of heart causing death of tissue and leading to heart attack or

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Functions of Circulatory System.

Types of Circulation.

Circulatory system in multicellular animals

Circulation of blood in prawn :

Important Tips

Heart of vertebrates

Heart.

(v) Internal structure

Differences between Neurogenic heart and Myogenic heart

(d) Factors affecting heart rate

Cradiac cycle

Heart sounds

Differences between first and seconds heart sounds

Electrocardiogram (ECG)

Blood vessels

(a) Histology of arteries and veins :

(c) Factors affecting blood pressure :

Types of blood circulation in human

(1) Ascending aorta

(iii) Internal iliac (Hypogastric)

Portal system

(i) Hypothalamo-hypophysial portal system :

Lymphatic system

(iii) Lymphatic system in human

(d) Types of lymphatic ducts : Two

Function of lymph nodes :

Important Tips

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