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 o Study of blood is called Haematology.

o Blood originates from Mesoderm.

o Blood formation is called Hemopoiesis and in adult human it takes place in BONE MARROW but during embryonic state it takes place mainly in liver (little blood also form in spleen and rib in embryo).

o Blood pH-7.4.

o Blood volume in a person is 1/13th part of total body weight.

o Special connective tissue

o Consisting of a fluid matrix, plasma, and formed elements.


o Straw coloured. Viscous fluid.

o Organic component of plasma is Constituting nearly 55 per cent of the blood.

o 90-92 per cent water + proteins 6-8 percent of it.

o Fibrinogen, globulins and albumins are the major proteins.

o Anticoagulant heparin is secreted by Mast cells prevent blood clotting in blood vessels.

o FIBRINOGENS are needed for clotting or coagulation of blood.

o GLOBULINS primarily are involved in defence mechanisms of the body

o ALBUMINS help in osmotic balance.

o Contains small amounts of minerals

  Na+ , Ca++, Mg++, HCO3 – , Cl– ,


o Glucose, amino acids, lipids, etc., are also present in the plasma as they are always in transit in the body.

o Factors for coagulation or clotting of blood are also present in the plasma in an inactive form.

o Plasma without the clotting factors is called SERUM.



o Constitute nearly 45 per cent of the blood.


o Erythrocytes or red blood cells (RBC) are the most abundant of all the cells in blood and found only in vertebrates.

o Frog RBC is largest and mammals have smallest RBC and in mammals Musk deer has smallest RBC.

o In a healthy adult man  5 millions to 5.5 millions of RBCs mm–3 of blood.

o RBCs are formed in the red bone marrow in the adults.

o RBCs are devoid of nucleus in most of the mammals

o RBCs are biconcave in shape.

o They have a red coloured, iron containing complex protein called haemoglobin, hence the colour and name of these cells.

o A healthy individual has 12-16 gms of haemoglobin in every 100 ml of blood.

o These molecules play a significant role in transport of respiratory gases.

o Hb has two parts haem (5%) and globin (95%).

o Iron in haem is in ferrous state.

o Globin is made up of 4 polypeptide chains (two alpha with 141 amino acids individually and 2 beta each with 146 amino acids) which are associated with Haem with co-ordinate bond.

o Haemolysis is bursting of RBC and it occur due to some fat solvent, snake venom .

o Haemolysis also occur when RBC is placed in hypotonic solution.

o Adhering together of RBC in pile /stack manner by their concave surface is ROULEAUX FORMATION. It occur whem fresh blood is placed on a slide under coverslip. This may also occur temporarly when blood flow slowly in vessels.

o ESR is erythrocyte sedimentation rate and it is measured by wintrobe tube/Westergren tube method.

o Men has lower ESR than female.

o RBCs have an average life span of 120 days after which they are destroyed in the spleen (graveyard of RBCs).

o Leucocytes are also known as white blood cells (WBC) as they are colourless due to the lack of haemoglobin.

o They are nucleated and are relatively lesser in number which averages 6000-8000 mm–3 of blood.

o Leucocytes are generally short lived (15 hrs to 2 days).

o Diapedeis is coming out of WBC from vessels. Increase in number of WBC is leucocytisis while decrease is leucopenia .

o Neutrophils, eosinophils and basophils --> GRANULOCYTES

o Lymphocytes and monocytes --> AGRANULOCYTES.

o Neutrophills are most abundant (60-65%), most active with 3-5lobed nucleus while Eosinophills are bilobed

,phagocytotic and associated with allergic and parasitic infestation.

o Basophils are phagocytotic and related with allergic reaction. Basophils secrete histamine, serotonin, heparin, etc., and are involved in inflammatory reactions.

o Basophils are the least (0.5-1 per cent) among WBC.

o Lymphocytes and monocytes are Agranular leucocytes and monocytes are largest WBC

o Lymphocytes (20-25 per cent) are of two major types – ‘B’ and ‘T’ forms.

o Both B and T lymphocytes are responsible for immune responses of the body.

o Platelets also called thrombocytes, are cell fragments produced from megakaryocytes (special cells in the bone marrow).

o Platelets are non-nucleated.

o Blood normally contains 1,500,00-3,500,00 platelets mm–3.

o Platelets can release a variety of substances most of which are involved in the coagulation or clotting of blood.

o A reduction in their number can lead to clotting disorders which will lead to excessive loss of blood from the body.


o Two groupings – the ABO and Rh – are widely used all over the world.

o ABO grouping is based on the presence or absence of two surface antigens (chemicals that can induce immune response) on the RBCs namely A and B.


o Similarly, the plasma of different individuals contain two natural antibodies (proteins produced in response to antigens).

o During blood transfusion, any blood cannot be used; the blood of a donor has to be carefully matched with the blood of a recipient before any blood transfusion to avoid severe problems of clumping (destruction of RBC).

o Group ‘O’ blood can be donated to persons with any other blood group and hence ‘O’ group individuals are called ‘UNIVERSAL DONORS’ (specifically O negative).

o Persons with ‘AB’ group can accept blood from persons with AB as well as the other groups of blood. Therefore, such persons are called ‘UNIVERSAL RECIPIENTS’.

o Rh Grouping  the Rh antigen  observed on the surface of RBCs of majority (nearly 80 per cent) of humans. Such individuals are called Rh positive (Rh+ve) and those in whom this antigen is absent are called Rh negative (Rh-ve).

o An Rh-ve person, if exposed to Rh+ve blood, will form specific antibodies against the Rh antigens.

o Therefore, Rh group should also be matched before transfusions.

o A special case of Rh incompatibility (mismatching) has been observed between the Rh-ve blood of a pregnant mother with Rh+ve blood of the foetus.

o Rh antigens of the foetus do not get exposed to the Rh-ve blood of the mother in the first pregnancy as the two bloods are well separated by the placenta.

o However, during the delivery of the first child, there is a possibility of exposure of the maternal blood to small amounts of the Rh+ve blood from the foetus.

o In such cases, the mother starts preparing antibodies against Rh antigen in her blood.

o In case of her subsequent pregnancies, the Rh antibodies from the mother (Rh-ve) can leak into the blood of the foetus (Rh+ve) and destroy the foetal RBCs.

o This could be fatal to the foetus or could cause severe anaemia and jaundice to the baby.

o This condition is called ERYTHROBLASTOSIS FOETALIS.

o This can be avoided by administering anti-Rh antibodies to the mother immediately

after the delivery of the first child.


o Blood exhibits coagulation or clotting in response to an injury or trauma.

o This is a mechanism to prevent excessive loss of blood from the body.

o A clot or coagulam formed mainly of a network of threads called fibrins in which dead and damaged formed elements of blood are trapped.

o Fibrins are formed by the conversion of inactive fibrinogens in the plasma by the enzyme thrombin.

o Thrombins, in turn are formed from another inactive substance present in the plasma called prothrombin.

o An enzyme complex, THROMBOKINASE, is required for the above reaction and thromboplastin help in formation of this


enzyme and thromboplastin is released injured tissue.

o This complex is formed by a series of linked enzymic reactions (cascade process) involving a number of factors present in the plasma in an inactive state.

o An injury or a trauma stimulates the platelets in the blood to release certain factors which activate the mechanism of coagulation.

o Certain factors released by the tissues at the site of injury also can initiate coagulation.

o Calcium ions play a very important role in clotting


o As the blood passes through the capillaries in tissues some water along with many small water soluble substances move out into the spaces between the cells of tissues  INTERSTITIAL FLUID OR TISSUE FLUID has the same mineral distribution as that in plasma.

o Exchange of nutrients, gases, etc., between the blood and the cells always occur through this fluid.

o An elaborate network of vessels called the lymphatic system collects this fluid and drains it back to the major veins.


o Lymph is a colourless fluid containing specialised lymphocytes which are responsible for the immune responses of the body.

o Lymph is also an important carrier for nutrients, hormones, etc.

o Fats are absorbed through lymph in the lacteals present in the intestinal villi.

o The process of lymph formation is called TRANSDUATION.



o Two types – open or closed.

o Open circulatory system is present in arthropods and molluscs

in which blood pumped by the heart passes through large vessels into open spaces or body cavities called sinuses.

o Closed circulatory system is present in Annelids and chordates

in which the blood pumped by the heart is always circulated through a closed network of blood vessels.

more advantageous  flow of fluid can be more precisely regulated.

o All vertebrates possess a muscular chambered heart.

o Fishes have a 2-chambered heart with an atrium and a ventricle.

o Amphibians and the reptiles (except crocodiles) have a 3-chambered heart with two atria and a single ventricle

o Crocodiles, birds and mammals possess a 4-chambered heart with two atria and two ventricles.

o In fishes the heart pumps out deoxygenated blood which is oxygenated by the gills and supplied to the body parts from where deoxygenated blood is returned to the heart (single circulation).

o In amphibians and reptiles, the left atrium receives oxygenated blood from the gills/lungs/skin and the right atrium gets the deoxygenated blood from other body parts. However, they get mixed up in the single ventricle which pumps out mixed blood (incomplete double circulation).

o In birds and mammals, oxygenated and deoxygenated blood received by the left and right atria respectively passes on to the ventricles of the same sides. The ventricles pump it out without any mixing up, i.e., two separate circulatory pathways are present in these organisms, hence, these animals have double circulation.

8. Human Circulatory System

o Consists of a muscular chambered heart, a network of closed branching blood vessels and blood, the fluid which is circulated.

o Heart, the mesodermal derived organ

o Heart is situated in the thoracic cavity, in between the two lungs, slightly tilted to the left.

o It has the size of a clenched fist.

o It is protected by a double walled membranous bag, PERICARDIUM, enclosing the pericardial fluid.

o Our heart has four chambers, two relatively small, thin walled upper chambers called ATRIA and two larger, thick walled lower chambers called VENTRICLES.

o AURICLES --> both auricles are separated from myomembranous partition called INTER AURICULAR SEPTA/INTERARTRIAL SEPTA.


o It is bigger than left auricle.

o It receives deoxygenated blood from superior vena cava, inferior vena cava.

o Superior vena/precaval cava brings deoxygenated blood from head and upper part of body and harvesian valve is present on the opening of precaval which allow the passage of blood into Rt.auricle.

o Inferior vena cava /post caval open in go right auricle through single opening and opening is bordered with vestige of eustachian valve.

o Post caval bring deoxygenated blood from middle and lower part of body.

o Right auricle also has coronary sinus brings deoxygenated blood from heart wall.

o Overall precaval, post caval and coronary sinus bring deoxygenated blood from all part of the body.


SA NODE or Sino-atrial node/SAN

o It also has SA node/pace maker/node of Keith/brain of heart/pulsation centre.

o SA node located at right wall of right atrium just below the opening of precaval.

o SA node is main tissue of heart and has highest degree of auto rhythmicity and generates rhythmic impulse called sinus rhythmia at the rate of 70-78/minutes.


o It is also located in right atrium near right auriculo-ventricular septum (near coronary sinus).

o It is also called reserve pacemaker /node of Tawara and Aschoff.

o AV Node/ATRIO-VENTRICULAR NODE/AVN conducts cardiac impulse generated from SA NODE but it can also generate rhythmic impulse NODAL RHYTHMIA @40-60/minutes.

o Bundle of His /A V bundle arise from AV nodes and it moves downward in the interventricular septum. RIGHT VENTRICLE:

Right ventricle is connected with right auricle through a thick fibrous tissue called the ATRIO- VENTRICULAR SEPTUM.

o The opening between the right atrium and the right ventricle is guarded by a valve formed of three muscular flaps or cusps, THE TRICUSPID VALVE /Right A V valve which is three muscular flap and prevent back flow of deoxygenated blood from ventricle to right auricle.

o Pulmonary aorta/arch arises from upper left corner of right ventricle through a single opening and divide into right and left pulmonary artery and supply deoxygenated blood to lungs for oxygenation.

o At the base of pulmonary aorta, semilunar valve present which allow blood to move from ventricle to aorta but prevent backflow .

o Right ventricle is smaller in size but has bigger cavity as it is less muscular than left ventricle. LEFT AURICLE:

o It receives oxygenated blood from four pulmonary vein (two from each lungs) through four opening.

o Left auricle open into left ventricle through bicuspid /Mitral valve which consists of 2 flaps/cusps.


o Cavity of left ventricle is smaller than right ventricle as it has more muscles and it produce more pressure on blood during contraction.

o Systemic aorta arises from here through a single opening and has 3 region ascending aorta, arch of aorta and descending aorta and supply oxygenated blood to whole body and it also has semilunar valve which prevent back flow of blood from aorta to ventricle.

o A bundle of nodal fibres, atrioventricular bundle (AV bundle) continues from the AVN which passes through the atrio-ventricular septa to emerge on the top of the interventricular septum and immediately divides into a right and left bundle.

o These branches give rise to minute fibres throughout the ventricular musculature of the respective sides and are called PURKINJE FIBRES.

o These fibres along with right and left bundles are known as BUNDLE OF HIS.

o The valves in the heart allows the flow of blood only in one direction, i.e., from the atria to the ventricles and from the ventricles to the pulmonary artery or aorta.

o These valves prevent any backward flow.

o The entire heart is made of cardiac muscles.

o The walls of ventricles are much thicker than that of the atria.

o A specialised cardiac musculature called the nodal tissue is also distributed in the heart Sa

o A patch of this tissue is present in the right upper corner of the right atrium called the SINO-ATRIAL NODE (SAN).

o Another mass of this tissue is seen in the lower left corner of the right atrium close to the atrio-ventricular septum --> ATRIO-VENTRICULAR NODE (AVN).

o The nodal musculature has the ability to generate action potentials without any external stimuli, i.e., it is autoexcitable.

o The number of action potentials that could be generated in a minute vary at different parts of the nodal system.


o The SAN can generate the maximum number of action potentials, i.e., 70-75 min–1 , and is responsible for initiating and maintaining the rhythmic contractile activity of the heart. Therefore, it is called the PACEMAKER.

o Our heart normally beats 70-75 times in a minute (average 72 beats min–1).


o The SAN generates an action potential which stimulates both the atria to undergo a simultaneous contraction – the atrial systole.

o This increases the flow of blood into the ventricles by about 30 per cent.

o The action potential is conducted to the ventricular side by the AVN and AV bundle from where the bundle of His transmits it through the entire ventricular musculature.

o This causes the ventricular muscles to contract, (ventricular systole), the atria undergoes relaxation (diastole), coinciding with the ventricular systole.

o Ventricular systole increases the ventricular pressure causing the closure of tricuspid and bicuspid valves due and prevent backflow of blood into the atria. This closure of tricuspid and bicuspid valve produces the first heart sound “LUBB” at the starting of contraction of ventricle so lubb sound is associated with ventricular systole.

o As the ventricular pressure increases further, (when pressure in ventricles are greater than systemic aorta and pulmonary aorta) the semilunar valves guarding the pulmonary artery (right side of ventricle) and the aorta (left side of ventricle) are forced open, allowing the blood in the ventricles to flow through these vessels into the circulatory pathways. This is the start of ventricular diastole which last for about 0.5 second.

o The ventricles now relax (ventricular diastole) and the ventricular pressure falls causing the closure of semilunar valves which prevents the backflow of blood into the ventricles. Rapid closure of semilunar valve at the starting of ventricular diastole produce second heart sound called DUP/diastolic sound.

o As the ventricular pressure declines, the tricuspid and bicuspid valves between atrium and ventricle are pushed open by the pressure in the atria exerted by the blood which was being emptied into them by the veins.

o The blood now once again moves freely to the ventricles. The ventricles and atria are now again in a relaxed (joint diastole) state, as earlier.

o Soon the SAN generates a new action potential and the events described above are repeated in that sequence and the process continues.

o This sequential event in the heart which is cyclically repeated is called the cardiac cycle and it consists of systole and diastole of both the atria and ventricles.

o The heart beats 72 times per minute, i.e., that many cardiac cycles are performed per minute.

o Atrial systole takes0.1 second while atrial diastole is 0.7 second.

o Ventricular systole takes 0.3 second while diastole last for 0.5 second.


o During a cardiac cycle, each ventricle pumps out approximately 70 mL of blood which is called the stroke volume.

o The stroke volume multiplied by the heart rate (no. of beats per min.) gives the cardiac output.

o Cardiac output=stroke rate X rate of heart it is 70ml X 72=5040ml/minute.

o Therefore, the cardiac output can be defined as the volume of blood pumped out by each ventricle per minute and averages 5000 mL or 5 litres in a healthy individual.

o The body has the ability to alter the stroke volume as well as the heart rate and thereby the cardiac output. For example, the cardiac output of an athlete will be much higher than that of an ordinary man.

o During each cardiac cycle two prominent sounds are produced which can be easily heard through a stethoscope. The first heart sound (lub) is associated with the closure of the tricuspid and bicuspid valves whereas the second heart sound (dub) is associated with the closure of the semilunar valves. These sounds are of clinical diagnostic significance.

10. Electrocardiograph (ECG)

o Electro-cardiograph is a device used to obtain an electrocardiogram (ECG).



o To obtained a standard ECG, patient is connected to the machinewith three electrical leads, two in wreast and one in left ankle which monitor the heart activity.

o ECG is a graphical representation of the electrical activity of the heart during a cardiac cycle.

o Each peak in the ECG is identified with a letter from P to T that corresponds to a specific electrical activity of the heart.

o The P-wave represents the electrical excitation (or depolarisation) of the atria, which leads to the contraction/systole of both the atria.

o The QRS complex represents the depolarisation of the ventricles, which initiates the ventricular contraction.

o The contraction starts shortly after Q and marks the beginning of the systole.

o The T-wave represents the return of the ventricles from excited to normal state (repolarisation).

o The end of the T-wave marks the end of systole.

o By counting the number of QRS complexes that occur in a given time period, one can determine the heart beat rate of an individual.Any deviation from normal shape indicates a possible abnormality or disease. Hence, it is of a great clinical significance.

11. DOUBLE CIRCULATION: It can be divided into three parts. Pulmonary circulation, cardiac circulation and systemic/greater circulation.


o The amount of blood present in surrounding of lungs and pulmonary blood vessels is about 12%

o The deoxygenated blood pumped into the pulmonary artery is passed on to the lungs from where the oxygenated blood is carried by the pulmonary veins into the left atrium.

o Cardiac circulation: The amount of blood present in the heart is 8%.

o A special coronary system of blood vessels is present in our body exclusively for the circulation of blood to and from the cardiac musculature.


The amount of blood which circulate rest of the body and it is 80%



o The oxygenated blood entering the aorta pumped by left ventricle is carried by a network of arteries, arterioles and capillaries to the tissues from where the deoxygenated blood is collected by a system of venules, veins and vena cava and emptied into the right atrium. This is

o The systemic circulation provides nutrients, O2 and other essential substances to the tissues and takes CO2 and other harmful substances away for elimination.

o A unique vascular connection exists between the digestive tract and liver called HEPATIC PORTAL SYSTEM.

o The vein which drains blood into organ other than heart is called portal vein.

o The hepatic portal vein carries blood from intestine to the liver before it is delivered to the systemic circulation.

o The hepatic portal vein supply the blood which has digested food like glucose and amino acids and in liver extra glucose is converted into glycozen ,ammonia is converted into urea etc

o In mammal’s renal portal system is absent as heart is four chambered so there is no mixing of oxygenated and deoxygenated blood.


o Normal activities of the heart are regulated intrinsically, i.e., auto regulated by specialised muscles (nodal tissue), hence the heart is called myogenic.

o In myogenic heart which is found in mollusc and vertebrates, the heart beat is initiated by nodal tissue that is specialised cardiac musculature means impulse of contraction originate itself in heart that is why heart removed from the body continue to beat for some time and THIS MAKE THE HEART TRANSPLANTATION POSSIBLE.

o In Neurogenic heart (heart of annelids and arthropods) heart beat is initiated by nervous system and in this case heart transplantation is not possible.

o A special neural centre in the medulla oblangata can moderate the cardiac function through autonomic nervous system (ANS).

o Neural signals through the sympathetic nerves (part of ANS) can increase the rate of heart beat, the strength of ventricular contraction and thereby the cardiac output.

o When there is moderate increase in CO2 in blood sympathetic nerve fiber stimulate SAN for increase in heart rate and increase in force of contraction (Trachycardia).


o When there is increase in o2 in blood ,the parasympathetric or 10th cranial nerve vagus nerve inhibite SANby producing acety;echolinewhich increase contraction time and decrease heartbeat (bradychardi).

o On the other hand, parasympathetic neural signals (another component of ANS) decrease the rate of heart beat, speed of conduction of action potential and thereby the cardiac output. (ncert lineFor above statement).

o VAGUS ESCAPE: stimulation of vagus nerve decrease the heart beat but its continuous stimulation do not show any further decrease. It is called vagus escape.

o Noradrenalin increase heart beat under normal condition while adrenalin increase heart rate at the time of emergency.

o Thyroxin also increase heart rate by increasing energy production.

o CO2 in more amount decrease heart rate. Increase in sodium ions in blood/in cardiac muscles decrease heart rate.

o Increase in Ca++ in blood increase heart beat but if Ca ions are injected in cardiac muscles, heart stopped in contracted phase called systolic arrest while injection of K+ stop impulse generation so heart stop in diastolic phase.



o Hypertension is the term for blood pressure that is higher than normal (120/80).

o In this measurement 120 mm Hg (millimetres of mercury pressure) is the systolic, or pumping, pressure and 80 mm Hg is the diastolic, or resting, pressure.

o If repeated checks of blood pressure of an individual is 140/90 (140 over 90) or higher, it shows hypertension.

o High blood pressure leads to heart diseases and also affects vital organs like brain and kidney.


o Coronary Artery Disease, often referred to as atherosclerosis, affects the vessels that supply blood to the heart muscle.

o It is caused by deposits of calcium, fat, cholesterol and fibrous tissues, which makes the lumen of arteries narrower.


o It is also called ‘angina pectoris’.

o A symptom of acute chest pain appears when no enough oxygen is reaching the heart muscle.

o Angina can occur in men and women of any age but it is more common among the middle-aged and elderly.

o It occurs due to conditions that affect the blood flow.


o Heart failure means the state of heart when it is not pumping blood effectively enough to meet the needs of the body.

o It is sometimes called congestive heart failure because congestion of the lungs is one of the main symptoms of this disease.

o Heart failure is not the same as cardiac arrest (when the heart stops beating) or a heart attack (when the heart muscle is suddenly damaged by an inadequate blood supply).



1. Naris among annelids has no heart and amphioxus in chordate has no heart.

2. Splenic vein is with maximum free Hb.

3. Coronary sclerosis that is narrowing of coronary arteries leading to severe chest pain (Angina pectoris).

4. Papillary muscles of ventricle of heart which is exclusive present in mammals, anchor the chordae tendinare and if there is weakning of papillary muscles/breaking of chordae tendinae ,the AV valve revertto auricle so it can not prevent back flow of blood in to auricle. This is called REGURGITATION so blood flow slowly in pulmonary artery.

5. During embryonic stage,there is no inter-auricular septum and in place of this there is septum primum and septum secondum and between these two septum ,a gap called FORAMEN OVALE is present.T here is a membranous flap called eustachian flap which do not allow the blood to go to lungs as lungs in foetus is non functional.At the time of birth this aperture is closed but depression remain in right auricle as fossa ovalis and in left atrium it is as fossa lunata.

6. During foetus stage as lungs is non functional ,blood from pulmonary aorta comes to systemic aorta through small duct called DUCTUS BOTALLI /DUCTUS ARTRIOSUS and soon after birth this duct is blocked and this structure is called ligamentum arteriosum. If this duct remain open then this condition is called PDA(patent ductus arteriosus) and resultant into mixing of blood which leads to blue baby.




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