Biology Chapter 18 Body Fluids And Circulations

Blood is called a connective tissue As it helps in the trasport of essential substances to the cells and carries waste substances fro there. It connects the body systems, transports oxygen and nutrients to all the parts of the body, and removes the waste products. Blood also has an extra-cellular matrix called plasma, with red blood cells, white blood cells, and platelets floating in it.

The evolutionary changes in pattern of heart among vertebrates are :
1. Fishe heart is two chambered, one auricle and one ventricle. In there is single circulation of blood. 

2. Amphibian heart : The heart of amphibians have 3 chambers i.e. two auricles and one ventricle. 

3. Reptilian heart : In reptiles heart is three chambered, but ventricle is also incompletely divided by incomplete interventricular septum. 

In crocodile, the heart is four chambered i.e. with wo auricles and two ventricles.

4. Avian and Mammalian heart : In avian and mammals, the heart is four chambered ie with two auricles and two ventricles and there is complete separation of pure and impure blood. 

In the human heart, the contraction is initiated by a special modified heart muscle known as sinoatrial node or the SA-node. It is located in the right atrium. The SA node has the inherent power of generating a wave of contraction and controlling the heart beat. Hence, it is known as the pacemaker. Since the heart beat is initiated by the SA node and the impulse of contraction originates in the heart itself, the human heart is termed myogenic. The hearts of vertebrates and molluscs are also myogenic.

Sino-auricular node is called pacemaker, because nerve impulse or wave of contraction starts from it and goes to both auricles. Since the SA node initiates and maintains the rhythmicity of the heart and maintains the pace of the heart beat, it is known as the natural pacemaker of the human body.

These are differences between lymph and Blood.

72 times.

The bicuspid or mitral valve is situated between the left atrium and the left ventricle. These valves play a crucial role in ensuring the unidirectional flow of blood from the atrium to the ventricles, or the ventricle to the aorta or pulmonary trunk. 

Tricuspid valves or is present between the right atrium and the right ventricle. The function of the valve is to prevent back flow of blood from the ventricle into the right atrium.

In sponges all cells are in direct contact with environment and its all requirements are directly met thus it does not require a circulatory system. 

Depolarisation of the ventricles.

Cockroach

Vasa vasorum are the network of small blood vessels that supply the walls of large blood vessels, such as elastic arteries (aorta) and large veins (vena cava).

ECG or Electrocardiogram - It is the the graphical representation of the electrical activity of the heart during a cardiac cycle. In this the electrical activity of the heart is recorded over a period of time using electrodes placed on the skin. 

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

The P-wave represents the electrical excitation (or depolarisation) of the atria. The QRS complex represents the depolarisation of the ventricles. The T-wave represents the repolarisation. The end of the T-wave marks the end of systole.

Tachycardia is an abnormally rapid heart rate.i.e. more than 100 times/minute.

Bradycardia is abnormally slow heart action or rate.

Inferior vena cava.

Haematology is the study of blood.

It deals with the study of blood vessels.

Hypertension - It is the increase in blood pressure. When the blood pressure is higher than normal pressure that is 120/80. High blood pressure leads to heart diseases and also affects vital organs like brain and kidney.

Depolarisation of the atria.

Repolarisation of the ventricles.

Atrial systole is the contraction of the atria. During this he blood is forced into the ventricles. It precedes ventricular systole and is indicated by the fourth heart sound. It increases the blood flow into the ventricle by 30 %. 

Plasma is the straw coloured, viscous fluid constituting nearly 55% of the blood. It comprises of water (90-90%) and protein(6-8%).The major proteins present are fibrinogen, globulin and albumin. It also contains many minerals like  Na+, Ca⁺⁺, Mg⁺⁺, HCO3^–, Cl^–, etc. Glucose, amino acids, lipids, etc., are also present. Factors for coagulation or clotting of blood are also present in the plasma in an inactive form. Plasma without the clotting factors is called serum.

It is the valve present in the left auriculoventricular valve with two cusps. It is also called mitral valve.

Serum

 7.4

12-16 gms.

The SAN or sinoauricular node is present in the right upper corner  of right atrium.

The bundle of His are the cardiac muscle fibers that conducts the electrical impulses that regulate the heartbeat, from the atrioventricular node in the right atrium to the septum between the ventricles and then to the left and right ventricles. The purkinge fibres alongwith right and left bundles are known as bundle of His. They are also called atrioventricular bundle.

The amount of blood the heart pumps through the circulatory system in a minute. 

The amount of blood put out by the left ventricle of the heart in one contraction is called the stroke volume.

Megakaryocytes.

Spleen

Landsteiner

Leucocytes

Haemostasis is the human body's response to blood vessel injury and bleeding. It involves a synchronised effort between platelets and numerous blood clotting proteins (or factors), resulting in the formation of a blood clot to prevent blood loss.

Basophils

Antigens are those chemical substances that can induce immunity.

The blood group is of four types
i. A
ii. B
iii. AB
iv. O

O (blood group)

Human heart has 4 chambers and there is complete separation of pure and impure blood. The right ventricle pumps blood to lungs for purification and left ventricle pump spure blood to all parts of the body for the supply of oxygen and receiving C0₂. Thus the human heart acts as double pump.

The closed circulatory system allows the the flow of the fluid to be precisely regulated as the fluid (blood) is circulated through a closed vessel. 

Phonocardiogram.

0.8 second.

0.1 second, 0.3 second and 0.4 second respectively.

0.7 second.

0.5 Second

The SA node or sino-atrial node (SAN) is called the the natural pacemaker of the heart. It controls the heart rate by generating electrical impulses and then sending electrical signals through the heart muscle, causing the heart to contract and pump blood throughout the body.The heart beat originates from S.A. node and spreads to the walls of auricles which contract. 

Serum consists of plasma from which fibrinogens have been removed. It contains antibodies to counter act the effect to toxic substances of micro-organisms. It is the plasma without the clotting factors.

The valves prevent the back flow of the blood. 

The walls of auricles thinner than walls of ventricles because auricles have to pump blood to ventricles which are lying below them and ventricles have to pump to all parts of the body. The thicker walls allow the ventricles to pump the blood to the different blood vessels with more force. 

The largest artery is the aorta, it is connected to the heart's left ventricle.

The heart wall is comprised of three layers: the outer epicardium, the middle myocardium, and the inner endocardium.

70 ml ( of blood pumped out of each ventricle)

5 litres. (the volume of blood pumped out of each ventricle per minute)

0.3m/second.

0.1 sec

The closure of tricuspid and bicuspid valves are associated with the first heart sound (Lub)

The closure of the semilunar valves are thought to produce the second heart sound (Dub).

The two types of circulatory pathways are:
i. Open circulatory pathway - In this type the blood
pumped by the heart passes through large vessels into open spaces or body cavities called sinuses. It is found in arthropods and molluscs
ii. Closed circulatory pathway - In this type the blood pumped by the heart is always circulated through a closed network of blood vessels. Annelids and chordates have a closed circulatory system.

The heart is called three chambered when it has two atria and a single ventricle. Amphibians and reptiles (except crocodiles have 3-chambered heart. 

30%

The Red blood cells (R.B.C), White blood cells (W.B.C) and platelets (thrombocytes) constitute the formed elements. 

Tissur fluid is the is a solution that bathes and surrounds the tissue. It is the fluid released out when the blood passes through the capillaries in the tissues. It consists of some water along with the many small water soluble substances. The tissue fluid is devoid of larger proteins and most of the formed elements found in blood. 

Lymph is the colourless fluid present in the lymphatic vessels. It contains specialised lymphocytes which are reponsible for providing immunity. It is also and carrier for nutrients . hormones etc. Fats are absorbed through lymph by the lacteals of the instetinal villi. 

Serum is devoid of clotting factor. Serum is the blood plasma without the fibrinogens which is the protein that helps in clotting. Thus, it does not clot as it lacks the clotting factors and fibrinogen necessary for the formation of the clot. 

A normal systolic blood pressure is 120.

A normal diastolic blood pressure number is 80. 

Angina pectoris or angina is the symptom of acute chest pain due to an inadequate supply of oxygen to the heart muscle.It occurs due to conditions that affect the blood flow. 

Cardiac arrest is when the heart stops beating. It is the sudden, unexpected loss of heart function, breathing and consciousness.

Capillaries have a single layer.  Capillaries consist of a single layer of epithelial cells, called the endothelium tunic (tunica intima).

Heart attack is when the heart muscle is suddenly damaged by an inadequate blood supply. 

Systole : It is contraction phase of heart. It is the phase of the heartbeat when the heart muscle contracts and pump blood in to the ventricles (atrial systole) or the arteries (ventricular systole)

Diastole : It is the relaxation phase of heart. It is that phase of the heartbeat when the heart muscle relaxes and allows the chambers to fill with blood.

Pulmonary circulation : It is the circulation of impure blood from right ventricle to lungs via pulmonary artery and collection of pure blood from lungs and pouring that to left auricle by pulmonary veins.

Lacteals.

Thrombin

Red pulp is the part of the spleen which has abundance of red blood cells and appears reddish brown in colour. It is reticular tissue rich in R.B.C. present in spleen.

White pulp is the parenchymatous tissue of the spleen that consists of compact masses of lymphatic cells in the form of small patches present in spleen. It is mainly made up of white blood cells.

Thrombokinase.

Calcium. 

Impure

Dorsal

Clotting

R.B.C.

The circulatory system performs the following functions :

(a) Transportation of gases : The gases like oxygen, carbon dioxide are transported from respiratory organs to every cell in the body. The oxygen is carried from lungs to body cells via heart and carbon dioxide from body cells to lungs.

(b) Transportation of nutrients : The different types of nutrients are transported to different cells.

(c) Transportation of waste products : The waste products like urea, uric acid, ammonia etc. are collected from different body tissues and poured into excretory organs.

(d) Transportation of water : Water and chemical substances are transported all over the body uniformly by blood.

(e) Transportation of hormones : The hormones secreted by the different endocrine glands are carried to their site of targets by blood.

The heart is myogenic that is it is auto regulated by specialised muscles (nodal tissue).
The cardiac acivity is regulated by the following:
i. A special neural centre in the medulla oblangata can moderate the cardiac function through autonomic nervous system (ANS).
ii. 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. 
iii. The parasympathetic neural signals decrease the rate of heart beat, speed of conduction of action potential and thereby the cardiac output.
 
iv. Adrenal medullary hormones can also increase the cardiac output.

Double circulation is a process during which blood passes twice through the heart during one complete cycle., i.e., two circulatory pathways, namely, pulmonary and systemic are present.
i. Pulmonary circulation - It  starts by the
pumping of deoxygenated blood by the right ventricle which is carried to the lungs
where it is oxygenated and returned to the left atrium.
ii. Systemic circulation - It starts with the pumping of oxygenated blood by the left ventricle to the aorta which is carried to all the body tissues and the deoxygenated blood from there is collected by the veins and returned to the right atrium. The systemic circulation provides nutrients, O2 and other essential substances to the tissues and takes CO2 and other harmful substances away for elimination.

Double circulation : It means that the blood passes through the heart twice,  through two separate pathways for completing one cycle. In double blood circulation the blood has two circulations pathways, namely, pulmonary and systemic are present.

1. Pulmonary circulation : It is the circulation in which impure blood from right. ventricle of heart goes to lungs and after purification (oxygenation) is poured back into the heart (left auricle).
Mechanism - In this the blood is pumped by the right ventricle enters the pulmonary artery, whereas the left ventricle pumps blood into the aorta. 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.

Right auricle Fig. Double circulation of blood in mammals

2. Systemic circulation : The systemic circulation starts with the pumping of oxygenated blood by the left ventricle to the aorta which is carried to all the body tissues and the deoxygenated blood from there is collected by the veins and returned to the right atrium.
Mechanism -  The oxygenated blood entering the aorta 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.
Significance of Double circulation
It  allows a highly efficient supply of oxygen to the body cells which is necessary for producing a lot of energy. This energy is useful in case of human beings that have high energy need because they constantly required energy to maintain their body temperature.  

Internal structure of human heart:

Human heart is four chambered. The two relatively small upper chambers called atria and two larger

i. Atria : There are two auricles that is the Right and left auricle. The auricles are thin walled because they have to push the blood only upto ventricles. Both atria are separated by a thin vertical interauricular septum which prevents mixing of oxygenated and deoxygenated blood. A depression called fossa oval is is present in interauricular septum which is a vestige of foramen ovale, present in the foetus.

Right auricle : It is larger in size than left auricle. It receives deoxygenated blood by superior vena cava (precaval) from upper portion of chest; inferior vena cava (post caval) from lower parts of body and coronary sinus from the wall of heart. Eustachian valve guards the opening of inferior vena cava and thebesian valve guards opening of coronary sinus. Right auricle opens into right ventricle via right auriculo-ventricular aperture which has a tricuspid valve. Tricuspid valve prevents the back flow of blood from ventricle to auricle.

Left auricle : It receives oxygenated blood from lungs by four pulmonary veins. These have no valves. Left auricle opens into left ventricle by a crescentric aperture called left auriculoventricular aperture. It is guarded by a bicuspid valve (mitral valve) which regulates blood from left auricle to left ventricle but checks the backflow of blood.

ii. Ventricles : The walls of ventricles are thicker than auricles. The walls of left ventricle is thicker than right ventricle because it has to pump the blood to all the parts of the body and right ventricle has to supply the blood only to lungs which are lying near the heart. The walls of ventricles have ridges and depression called columnae carneae and fissures respectively. These increase the surface area. The walls of ventricles have conical muscles called papillary muscles. Both ventricles are separated by a thick vertical interventricular septum which is obliquely placed. The septum has muscles called Bundle of His which gets branched and enter into walls of ventricles. The branches further get branched and the final branches are called Purkinje fibres.

Pulmonary arch arises from left side at anterior end of right ventricle. It has three semilunar valves at its beginning. The pulmonary aorta divides into two pulmonary arteries which supply deoxygenated blood to lungs.

The systemic aorta arises from right side of left ventricle at anterior end. It also has three semilunar valves at its beginning. The systemic aorta is connected to pulmonary aorta by ligamentum arteriosum.

Fig. L.S. of heart showing internal sturcture 

The Left ventricle possesses thicker walls than the right ventricle because the left ventricle has to pump the purified blood to all the parts of the body, whereas right ventricle's function is to pump the deoxygenated blood just to the lungs for purification which are lying near the heart. The thicker walls allow the blood to be pumped forcefully to different parts away from the heart. 

Double circulation system has the following main advantages over single circulation :

1) The ability to create more pressure to pump blood round the system.
2) The separation of oxygen-rich and oxygen-poor blood.
3) Better distribution of the nutrients, oxygen etc. 

Pace maker is a neuro muscular structure which produces and regulates cardiac impulses. Natural pacemaker is sino-atrial node (SA node).
The SAN is a patch of cardiac musculature tissue present in the right upper corner of the right atrium. It has the ability to generate action potentials without any external stimuli, i.e., it is autoexcitable. 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. 

Artificial pacemaker is a medical device which uses electrical impulses, delivered by electrodes contracting the heart muscles, to regulate the beating of the heart.
Sometimes the SAN i.e. pacemaker gets damaged and fails to generate cardiac impluses. This defect can be corrected by installing an artificial apparatus or pacemaker in the chest of the patient. Artificial pacemaker is connected to right ventricle. The apparatus stimulates the heart electrically at regular time intervals and maintains the heart beat.

Oedema is the condition characterized by an excess of watery fluid collecting in the cavities or tissues of the body.
When the rate of lymph formation exceeds due to the increase in permeability of capillary walls than the rate of its return to blood, it results in accumulation of lymph around the cells. This causes swelling of tissues or organs called oedema.

The heart beat originates from SAN (sino-atrial node )and passes to AVN (auriculo-ventricular node). The impulse is then picked up by the bundle of His,  which lpasses to the network of Purkinje fibres.
The bundle of His is essential for the conduction of cardiac impulse because it forms the continuity between arterial and ventricular muscles. It transmits impulses from the atrioventricular node, located at the inferior end of the interatrial septum, to the ventricles of the heart

Portal system is the system of blood vessels consisting of the hepatic portal vein with its tributaries and branches. It exists between the digestive tract and liver. 
It is the system when veins collect blood from some parts of body and pour it into some other parts of body instead of taking it directly to heart. The hepatic portal vein carries blood from intestine to the liver before it is delivered to the systemic circulation.

Joint diastole is the phase during which auricles and ventricles are in diastole or in the relaxed state. During this phase, the blood through veins enters into the respective auricles. The blood flows to the respective ventricles. No blood flows out of ventricles and the semi lunar valves remain closed.

Single circulatory system. In the circulatory system of a fish, the blood travels from the heart to the gills, where it absorbs oxygen and releases carbon dioxide. It then flows from the gills to the organs and tissues in the rest of the body, and back to the heart. There is just one circuit from the heart.
Advantages :
 The blood circulating in the body has already been oxygenated in the gills.

Disadvantages:
Due to lower pressure the rate of delivery of oxygen is slow. This lowers the metabolic rate. The nutrients are not properly distributed. 

The factors which affect the rate of pace-maker potential also influence the rate of heart beat.
The main factors are:

1. Temperature : The velocity of the conduction of action potential and level of resting membrane potential are directly related to the temperature.

2. Neural signals through the sympathetic nerves increase the hearbeat rate. 
3. A special nerve centre in the medulla oblangata can effect the heart beat rate. 

3. Chemical transmitters and hormones.

(i) Acetylcholine tends to reduce the rate of heart beat.

(ii) Norepinepherine liberated from sympathetic nerveous system, increases the rate of heartbeat per minute.

(iii) Hormone adrenaline, secreted from adrenal cortex, also increases the heart beat rate.

Lymph : It is described as filtered blood plasma having lower protein content. It is clear, watery fluid, that flows through lymphatic vessels, It is a link between blood and tissue fluid. It contains :

(i) fluid plasma with low protein content and
(ii) lymphocytes that squeeze out of capillary walls.

Functions of lymph :

(i) It helps in the distribution of nutrients, hormones  etc .

(ii) Fats are absorbed through the lymph in the lacteal present in the intestinal villi. 

(iii)  It helps in providing immunity.
(iv) It controls concentration of proteins in the tissue fluid.

Lymphatic system  is part of the circulatory system and a vital part of the immune system, comprising a network of lymphatic vessels that carry a clear fluid called lymph, directionally towards the heart.
Location :

Lymph nodes are abundant in neck, arm-pit and groin. Tonsils and adenoids are important lymphatic organs of the body.

Functions :

(i) Produce lymphocytes and monocytes.

(ii) Synthesize certain antibodies.

(iii) Phagocytose and destory bacteria and other pathogens.
(iv) Absorbs fats. 
(v) Carry nutrients and hormones. 

Some heart diseases are as follows:

i. Coronary Artery Disease (CAD): It is often referred to as atherosclerosis. It affects the vessels that supply blood to the heart muscle. It is caused by deposits of calcium, fat, cholesterol and fibrous tissues, which makes the lumen of arteries narrower.
ii. Angina: Also known as ‘angina pectoris’. It is the acute chest pain that appears when the oxygen reaching the heart muscle is not enough. It may occur in men and women of any age but it is more common among the middle-aged and elderly. It occurs due to conditions that affect the blood flow.
iii. Heart Failure: It is the state when heart does not pump blood effectively enough to meet the needs of the body. It is sometimes
called congestive heart failure because congestion of the lungs is one of
the main symptoms of this disease.
iv. Cardiac arrest - It is when the heart stops beating
v. Heart attack - It is when the heart muscle is suddenly damaged by an inadequate blood supply.
vi. High Blood pressure - It is also called as hypertension and occures when the blood pressure remains 140/90 or higher 
vii. Coronary thrombosis : It is the blockage of coronary artery due to the presence of a small clot or thrombus. This also leads to insufficient or no supply of blood to the heart muscles.

Electrocardiogram (ECG) : is a graphical representation of the electrical activity of the heart during a cardiac cycle

Electrocardiography is the process of recording the electrical activity of the heart over a period of time.
Mechanism - It is done by using electrodes placed on the skin. To record an ECG, a patient is connected to the machine with three electrical leads (one to each wrist and to the left ankle) that continuously monitor the heart activity. For a detailed evaluation of the heart’s function, multiple leads are attached to the chest region.

The impulse conduction generates tiny electrical currents in the heart which spread through surrounding tissues to the surface of the body. The electrodes placed on the body surface at specific places, record the electric potentials generated by the heart during the transmission of impulse from SA node.  

A typical E.C.G. is composed of wave ‘P’, a ‘QRS’ complex and ‘T’ wave.
i. The ‘P’ wave represents atrial depolarization. 
‘ii QRS’ is a wave generated by the spread of the process of excitation through ventricles.
iii. T wave is generated as the ventricles recover from the state of depolarization.

Significance :
The significance of ECG is that it tells the defect in the functioning of heart.

Blood pressure : The force which the blood applies against the walls of blood vessels is known as blood pressure.
The pressure of the blood in the circulatory system depends upon :

1. Changes of the circulatory space due to contraction and relaxation of heart and blood vessels.

2. The amount of blood entering and leaving the blood vessels.

3. Total blood volume.

4. The viscosity of blood.

5. The elasticity of the blood vessels.

Systolic pressure : It is the pressure of blood during systolic phase. It is maximum and is responsible for the movement of blood in the arteries. Normal systolic pressure is 120—130 mm of Hg.

Diastolic pressure : It is the blood pressure during diastolic phase of heart when blood is received in the heart. Normal diastolic pressure is 80 mm of Hg. 

The blood pressure is measured by the instrument called sphygnomanometer.

i. Embolus : It is a clot that forms in one part of body, flows with the blood stream and lodges on a blood vessel at a point some distance from the site of its formation.

ii. Thrombus : It is a blood clot, which stays where it is formed e.g. coronary thrombus.

iii. Thrombophilia : is a condition where the blood has an increased tendency to form clots. 

iv. Vasodilation : refers to the widening of blood vessels. 

v. Thrombocytopenia : deficiency of platelets in the blood. This causes bleeding into the tissues, bruising, and slow blood clotting after injury.

vi. Acapnia : It is the deficiency of C0₂ in the blood.

vii. Pulse pressure : The difference between systolic and diastolic pressure is termed as pulse pressure.

Blood performs the following functions :

1. Transportation of oxygen.

2. Transportation of carbon dioxide.

3. Transportation of various hormones.  

4. Healing up of injured parts : At the point of injury, clotting occurs and thus the blood helps in healing up of the injured part.

5. Transportation of the metabolic waste products : The blood takes metabolic waste products from all cells and supply them to kidneys.

6. Antibodies : The antibodies of plasma neutralize the toxic substances produced by bacteria.

7. Protection from diseases : The neutrophils engulf the foregin bacteria and thus protect human beings from diseases.
8. Distribution of various nutrients throughout the body. 

Blood clotting : It is the natural device to check bleeding. The clot is a reddish brown scum which is formed at the site of a cut or an injury over a period of time. The clot consists mainly of a network of threads called fibrins in which dead and damaged formed elements of blood are trapped.
An injury or a trauma stimulates the platelets in the blood to release certain factors which activate the mechanism of coagulation. Certain
factors released by the tissues at the site of injury also can initiate coagulation. Calcium ions play a very important role in clotting.

i. The fibrins are formed by the conversion of inactive fibrinogens in the plasma by the action of the enzyme thrombin.
ii. Thrombins, in turn are formed from another inactive substance present in the plasma called prothrombin. This reaction is brought about by the enzyme thrombokinase. TThe clot is formed by a series of linked enzymic reactions (cascade process) involving a number of factors present in the plasma in an inactive
state. 

Blood contains formed elements. Erythrocytes, leucocytes, and platelets are collectively known as formed elements. 
i. Erythrocytes - They are also called Red Blood Corpuscles (RBCs). They are the most abundant elements present in the blood. RBCs are formed in the red bone marrow in the adults. They are devoid of a nucleus.
Their main function is the transport of the respiratory gases.
ii. Leucocytes - They are also called White Blood Corpuscles (WBCs). They are nucleated and less abundant as compared to the RBCs. The WBCs are further divided into granulocytes and agranulocytes. The granulocytes are of three types neutrophils, eosinophils and basophils. Monocytes and lymphocytes constitute the agranulocytes. The lymphocytes are further 
The main function is to provide immunity to the body against the pathogenic organisms. 
iii. Platelets -  They are also known as thrombocytes. Platelets are small irregular bodies present in the blood. They contain essential chemicals that help in clotting.
The main function of platelets is to promote clotting.

Plasma  proteins constitute 6-8% of the plasma. Fibrinogen, globulins, and albumins are the major proteins of the plasma. 
Following are the importance of the plasma proteins:
i. Fibrinogens - these are required for the clotting and coagulation of the blood. 
ii. Globulins - these are involved in the  defence mechanism.
iii. Albumins are required for maintaining the osmotic balance. 

The atrioventricular (AV) node is present in the right atrium, near the base of the inter-auricular septum that separates the right auricle from the ventricle. It gives rise to the bundle of His. The Bundle of HIS conducts the cardiac impulses from the auricles to the ventricles. As the bundle of His passes the ventricle along the inter-ventricular septum, it divides into two branches - the right ventricle and the left ventricle.

The end branches of this conducting system then forms a network of Purkinje fibres that penetrate into the myocardium. The auricular contraction initiated by the wave of excitation from the sino-atrial node (SA node) stimulates the atrio-ventricular node, thereby leading to the contraction of ventricles through the bundle of His and Purkinje fibres. Hence, the atrio-ventricular node and the atrioventricular bundle play a role in the contraction of ventricles.

The cardiac cycle produces a characteristic sound that is usually referred to as the heart sounds. Lub- Dub is referred to as the heart sound. 

Lub is the first heart sound. It is associated with the closure of the tricuspid and bicuspid valves at the beginning of a systole.
Dub is the second heart sound. It is associated with the closure of the semilunar valves at the beginning of diastole.

B.

decrease the affinity of haemoglobin with oxygen

Reduction in pH of blood that is an increase in acidity favours the dissociation of oxyhaemoglobin thereby giving up more O_2. phenomenon occurs due to increase in C0_{2 concentration then it is called Bohr effect.} 

B.

more than that in the pulmonary vein

Blood pressure in different blood vessels:
Artery > arteriole > capillary > venule> vein (Vena cava)

A.

Contraction of both the atria

In ECG, P - wave represents the depolarization of atria which leads to contraction of both atria. T- wave represents the return of ventricles from excited to a normal state. The QRS complex represents the depolarisation of the ventricles which initiates ventricular contraction. The contraction starts shortly after  Q and marks the beginning of systole.

C.

Whale

The circulatory system in which two distinct and separate circulatory pathways for blood flow are involved, is called double circulatory system(also double-loop circulatory system). It occurs in mammals and birds whale is a mammal so it shows above characteristic.

C.

Semilunar valves close down after the blood flows into vessels from ventricles

In healthy adults, there are two normal heart sounds often described as lubb and dup. These are the first heart sound and second heart sound produced by closing of the AV valves and semilunar valves respectively.

C.

Blood group O

Blood group is tested by two types of sera i.e., anti-A (antibody-A) and anti-B (antibody-B). Persons with blood group O Possess both antibodies in their plasma but have no antigens in their RBCs. So, RBCs of blood group 'O' do not show clumping in way of the sera. That's why, persons with blood group 'O' are called universal donor and they can donate blood to a person with any type of blood group.

A.

Phagocytosis is an important feature of cellular innate immunity, performed by cells called phagocytes that engulf or eat pathogens or foreign particles. Common examples of these phagocytes are monocytes, macrophages, neutrophil granulocytes (often referred to as polymorphonuclear leukocytes or PMN or PML, because of the varying shapes of nucleus), tissue dendritic cells, mast cells etc. Antitetanus and anti snake bite injections are examples of passive immunity. 

C.

Phosphorus is a constituent of cell membranes, certain nucleic acids and all proteins

Phosphorus is a component of DNA and RNA but not proteins.

A.

Have more RBCs and their haemoglobin has a lower binding affinity of O₂

As a person moves up a hill the pO₂ and total atmospheric pressure decreases. Decrease in pO₂ due to increasing altitude, stimulates the JG-cells of kidney to secrete erythropoietin hormone, increasing the number of RBCs (polycythemia) to compensate the supply of O_2. At higher altitude, haemoglobin has lower binding affinity to O₂ because the primary factor responsible for binding is pO₂, which decreases at higher altitude. 

C.

Spleen

The average life span of human RBCs is 120 days. The aged RBCs attract autoantibodies after which they are attached by macrophages in liver and spleen. Spleen is also called as graveyard of RBCs. The process of destruction of RBCs is called haemolysis. About 2.5 million RBCs destroyed every second in body.

C.

systole of the left ventricle

Blood pressure in the mammalian aorta is maximum during systole of the left ventricle because the heart shrinks and pushes loads of blood into aorta. It drives blood through the aortic valve to the body and organs except lungs. As the pressure in the aorta travels down into the distributing arteries the characteristics changes in diastolic and systolic pressures are observed. There is very small decline in arterial pressure due to the low resistance of large distributing arteries. 

D.

Blood = Plasma + RBC + WBC + Platelets

Blood contains Red Blood cells (RBCs), White Blood cells (WBCs) and platelets (-45% of volume) suspended in plasma (~ 55% of volume).
Lymph contains WBC especially lymphocytes, floating in lymph plasma.
Serum is the part of blood that is like water and that contains antibodies which fight against disease.
Blood plasma is pale yellow liquid component that contains water (up to 95% by volume) and dissolved proteins (6-8%) which contains serum, globulins and fibrinogen and also glucose, clotting factors, electrolytes (Na^+, Ca^2+, Mg²⁺,  etc).

B.

A, B, AB and O

Blood group of parents A and B will have off springs of A, B, AB and O are blood groups. The alleles of both the parents of A and B blood groups will form gametes with given alleles as shown in table below. 
This table gives the probable possibilities of blood groups by random fusion of gametes in offspring born to parents of blood groups A and B.

C.

Carry blood from one visceral organ to another visceral organ

Arteries are blood vessels that carry blood away from the heart toward different organs. They generally contain oxygenated blood (except pulmonary artery which contains deoxygenated blood). The blood flows in an artery under alternate increased pressure and with jerks.

C.

190/110 mmHg may harm vital organs like brain and kidney

Hypertension is the term for blood pressure that is higher than normal (120/80). In this measurement, 120 mm Hg (millimeter of mercury pressure) is the systolic, or pumping, pressure and 80 mm Hg is the diastolic, or resting pressure. If repeated checks of blood pressure 190/100 mm Hg) of an individual is 140/90 (140 over 90) or higher, it shows hypertension. High blood pressure (190/100 mm Hg) leads to heart diseases and also affects vital organs like brain and kidney. 

A.

Heart

The bundle of his known as AV bundle (atrio ventricular bundle) is a collection of heart muscles cells specialised for electrical conduction. These specialised muscle fibres in cardiologist wilhelm His, Jr., Who discovered them in 1893.

C.

Fibrinogen 

Fibringoen (factor 1) is a soluble plasma glycoprotein, synthesised by the liver. It is converted by thrombin inot fibrin during blood coagulation. Fibrin is the cross - linked by factor XIII to form a clot.