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Circulation In Animal

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


Transport of various substances such as nutrients, waste products, respiratory gases, metabolic intermediates (Such as lactic acid from muscle to liver), vitamins hormones etc.

Regulation of body pH by means of buffer, body temperature homeostasis, water balance etc.

Prevention of disease by means of antibodies and antitoxins.

Support or turgidity to certain organs like penis and nipples.

2. Types of Circulation.

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

(i) Intracellular circulation : Occurs inside the individual cells where the distribution of substances is throughcyclosis of cell cytoplasm. Example –Protozoans.

(ii) Extracellular circulation : When the distribution of the substances occurs inside the body through extracellular or intracellular fluids. This is of following types –

(a) 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.

(b) Intra-organismic circulation : It involves circulation of body fluids. It is of following types :

(1) Parenchymal circulation : In platyhelminthes, the fluid filled spaces present in themesodermal parenchyma tissue between body wall and internal organs are used in the distribution of substances.

(2) Coelomic circulation : Coelomic fluid is concerned with the transport of substances. Example –pseudocoelomic fluid in the roundworms and haemolymph in Arthropods.

(3) Blood vascular system : It contains blood and a pumping structure (heart) for circulation of materials inside the body. It is of following types –

(i) Open circulatory system

(ii) 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 calledlacunae andsinuses among the tissues.

(1) In closed circulatory system blood flows through a closed system of chambers calledheart and blood vessels.

(2) Tissues are indirect contact with the blood.

(2) Blood doesnot come in direct contact with tissue.

(3) Bloodflow is very slow and blood has very low pressure.

(3) Bloodflow is quite rapid and blood has a high pressure.

(4)Exchange of gases and nutrients takes placedirectly between blood and tissues.

(4) Nutrients and gases pass through thecapillary wall to thetissue fluid from where they are passed on to thetissues.

(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 thesmooth muscles of the blood vessels.

(6) Open circulatory system is found inhigher invertebrates like most arthropods such as prawn, insects, etc., and in some molluscs.

(6) closed circulatory system is found inechinoderms, some molluscs, annelids and all vertebrates.

(7) Respiratorypigment, if present, isdissolved in plasma; RBCs are not present.

(7) Respiratorypigment is present and may be dissolved in plasma but is usually heldin RBCs.


Circulatory system of cockroach is of open type and is formed of three parts.

Body cavity of cockroach is called haemocoel as it is a pseudocoel filled with blood. It is divided into three sinuses by two fenestrated diaphragms Dorsal or pericardial diaphragm and ventral or sternal diaphragm. These three sinuses are: dorsal pericardial sinus, middle perivisceral sinus and ventral perineural sinus. The dorsal sinus is with heart and alary muscles, middle sinus is with most of visceral organs like gut, tracheae, reproductive organs, etc. while ventral sinus is with nerve cord. Head contains small sized spaces called head sinuses.

Blood circulation in vertebrates : Blood circulation was discovered byWilliam harvey. In case of vertebrates, blood circulation is ofclosed 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 cycle.

(1) Blood flows in two circuit pulmonary and systemic.


(2) Heart pumps only deoxygenated blood, hence calledVenous Heart.

(2) Heart pumps both deoxygenated and oxygenated blood to lungs and body respectively, hence calledarteriovenous 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.

Heart of vertebrates

Class of vertebrates




(1) Pisces (= Branchial heart)

Thick, muscular, made of cardiac muscles, has two chambers (i) auricle and (ii) ventricle. The heart is called venous heart since it pumps deoxygenated blood to gills for oxygenation. 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

(a) Two auricles

(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.




(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


(5) Mammals

Same as bird except that mammals have left systemic arch.                                                                                 

Rabbit, man

  • Haemolysis. It is destruction of red blood corpuscles with release of haemoglobin into plasma. It results in jaundice.

  • Leucopenia. An unusual lack of white blood corpuscles in the blood.

  • Haemorrhage. Haemorrhage is excessive loss of blood. The loss of blood decreases both the arterial and venous pressure.

  • The term homeostasis was given by an American physiologist Walter B. Cannon (1871–1945).

  • Blue Whale has the largest heart in the whole world.

  • The most important factors in heart diseases are cigarette smok ing, lack of exercise and over weight.

  • Cardiomegaly. Heart enlargement.

  • Angiology. Study of blood vascular and lymphatic systems.

  • Willian Harvey(1578-1657) is regarded as the father fo modern physiology.

  • Largest vein in human body–inferior vena cava.

  • Largest Artery—Aorta.

  • Smallest blood vessel in the body—blood capillary.

  • The giraffe’s blood pressure may be the highest.

  • One species of Antarctic fish is the only fish known to have white blood. It has no red pigment in its blood.

  • At birth the number of WBCs is more than the RBCs.

  • Frog has two pairs of lymph hearts.

  • A person feels sleepy after a heavy meal and is not able to concentrate his mind on serious matters because there is no sufficient blood to fill all the blood vessels at a given time, so more blood is directed towards alimentary canal and less blood towards the brain.

  • Angiography. X-ray of the blood vessels after injection of ratio-opaque substance.

  • Coronary Angiography. When the contrast medium dye is injected in coronary arteries (arteries of heart) and pictures are taken, it is known as coronary angiography.

  • In arborisation heartblock, the defect lies in the Purkinje’s fibres.

  • With removal of spleen, the leucocytes count rises.

  • Spleen is absent in cyclostomes.

  • Excess calcium ions cause increased heart beats.

  • Highest haemoglobin percentage is in neonates (newly born 14.5–24.5 per cent).

  • RBCs fail to mature if there is a deficiency of vitamin12and folic acid.

  • Right and left auricles (atria) of the mammalian foetus are connected through foramen ovale. Foramen ovale closes by the time of birth by a flap-like valve.

  • The heart is wrapped around the rectum of fresh water mussel. It means the rectum of fresh water mussel passes through the heart.

  • Keber’s organs or pericardial glands discharge excretory products into the pericardial cavity in the fresh water mussel.

  • A ‘‘Blue baby’’ is the name given to an abnormal human baby who has a hole in the ventricular septum through which more oxygenated and less oxygenated blood mix.

  • At higher altitude the blood volume increases.

  • The spleen is often referred to as ‘‘graveyard’’ of RBCs.

  • Adventitia. Outer most covering of any organ or structure specifically the outer coat of an artery, the tunica adventitia.

  • Renal vein carries the least amount of urea. However hepatic vein carries maximum amount of urea.

  • An insect larva has red blood. the larva of genus Chironomus is called ‘Blood worm’. The red colour of this larva is due to haemoglobin, which has the power of attracting and storing oxygen and giving it off to the tissues as they require it. Such larva is able to live in burrow it constructs in the mud.

  • Foramen of Panizzae : Aperture between two systemic arches in the reptiles.

  • Gubernaculum cordis : A white fibrous band which attaches apex of lizard heart to pericardium.

  • Valves in heart were first reported by Fabricius.

  • Heart forms 0.45% of body weight in male while it forms 0.40% of body weight in female.

  • There is about 15 ml of pericardial fluid in pericardium of human heart.

  • Human heart needs more oxygen supply so does not beat even in Ringer’s physiological solution.

  • Oedema : Swollen body part due to blockage of lymph vessels.

  • Ductus arteriosus : Also called duct of Botalli, is present in embryonic heart of mammals and connects pulmonary arch and aortic arch.

  • Haemodialysis : Separation of nitrogenous wastes from blood with the help of an artificial kidney.

  • Blood letting : Blooding a person for treatment.

  • Copraemia : Poisoning of blood from retained faeces.

  • Systolic blood pressure is higher limit of arterial blood pressure cycle and indicates force exerted by blood.

  • Diastolic blood pressure is lower limit of blood pressure cycle and indicates elasticity of blood vessel.

  • Negative blood pressure is recorded in great veins.

  • Hypertension is commonly called silent killer as has no noticeable symptoms. About 16% Indians suffer from hypertension.

  • Myogenic heart is found in molluscs and vertebrates. It is also called autorhythmic heart.

  • Ringer’s solution is formed of sodium and potassium salts.

  • Cardiovascular Accident (CVA) or Stroke : Reduction or stoppage of blood supply to brain due to sclerosis or thrombosis or haemorrhage of carotid artery. It leads to paralysis.

  • Heart pumps about 7,000 litres of blood per day.

  • B-Lymphocytes have the capacity to produce specific antibodies even during their development and differentiation.

  • Two important groups of antigens are : ABO-system and Rh-system.

  • ELISA-test : Enzyme-linked Immunosorbent Assay : A sensitive test for detection of antigens and antibodies by means of a specific enzyme e.g.AIDS.

  • Peripheral lymphoid organs : Lymph nodes, spleen (largest lymphoid organ) tonsils and Peyer’s patches.

Differences between Neurogenic heart and Myogenic heart

Neurogenic heart

Myogenic heart

(1) The heart beat is initiated by a ganglion situated near the heart.

(1) The heart beat is initiated by a patch of modified 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 molluscsand vertebrates.

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 45cycles per second.

(4) Its principal frequency is 50cycles per second.

Differences between arteries and veins







Thick, more elastic, non collapsible.

Thin, less ealstic, collapsible.


Tunica externa

Less developed, so less strong.

More developed, so more strong.


Tunica media

More muscular and has many elastic fibres.

Less muscular and only a few elastic fibres.


Tunica interna

Endothelial cells more elongated. Elastic membrane more developed.

Endothelial cells less flat. Elastic membrane less developed.







Deep seated except wrist, neck etc.




Without valves.

With valves to prevent back flow.


Direction of blood flow

From heart to body organs

From body organs to heart


Nature of blood

Oxygenated except pulmonary artery.

Deoxygenated except pulmonary vein


Blood pressure

More, generally 120/80 mmof Hg.

Less, generally 0 mmof Hg.


Speed of blood




After death

Becomes empty

Contain blood


Amount of blood

15% at any given time.

64% at any given time




Dark red





Differences between lymph and blood










Blood platelets





Persent, generally 7000/cu mm

Persent, generally 500-75000/cu mm






Albumin : globulin

Albumin  >Globulin

Albumin>  Globulin






Coagulation property                              




Direction of flow

Two way, heart to tissues and tissues to heart

One way, tissues to heart


Rate of flow




Glucose, urea and CO2



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