Layers in arteries:
Tunica Intima: This is the inner lining and is composed of squamous endothelium.
Tunica media: This is the middle layer and is composed of smooth muscles and elastic fibres.
Tunica externa: This is the external layer and is composed of collagen fibres.

His WBC count may show an increase from the normal range. As pathogens may be present in his body so the body is producing more WBCs to fight against those pathogens. WBC count is a good tool to asses presence of infection in a sick person.

During one cardiac cycle or one heartbeat, the volume of blood pumped by the heart is called stroke volume. This is normally 70 mL.
In one minute the heart beats about 72 times and the amount of blood pumped per minute is called cardiac output. This is usually 4900 mL ~ 5 litres.

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

Normal activities of the heart are regulated intrinsically, i.e., autoregulated by specialised muscles (nodal tissue), hence the heart is called myogenic. A special neural centre in the medulla oblongata can moderate the cardiac function through autonomic nervous system (ANS). Neural signals through the sympathetic nerves (part of ANS) can increase the rate of heartbeat, the strength of ventricular contraction and thereby the cardiac output. On the other hand, parasympathetic neural signals (another component of ANS)decrease the rate of heartbeat, speed of conduction of action potential and thereby the cardiac output. Adrenal medullary hormones can also increase the cardiac output.

Rh Incompatibility of Foetus and Mother. 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. 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. However, during the delivery of the first child, there is a possibility of exposure of the maternal blood to small amounts of the Rh +veblood from the foetus. In such cases, the mother starts preparing antibodies against Rh in her blood. 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. This could be fatal to the foetus or could cause severe anaemia and jaundice to the baby. This condition is called erythroblastosis foetalis. This can be avoided by administering anti-Rh antibodies to the mother immediately after the delivery of the first child.

(a) Erythrocytes. They are also known as Red Blood Cells (RBC). They are the most abundant of all the cells in blood. A healthy adult man has, on an average, 5 millions to 5.5 millions of RBCs mm^-3 of blood. RBCs are formed in the red bone marrow in the adults. RBCs are devoid of nucleus in most of the mammals and are biconcave in shape. They have a red coloured, iron-containing complex protein called haemoglobin, hence the colour and name of these cells. A healthy individual has 12-16 gms of haemoglobin in every 100 ml of blood. These molecules play a significant role in transport of respiratory gases. RBCs have an average lifespan of 120 days after which they are destroyed in the spleen. Hence, spleen is also known as the graveyard of RBCs
(b) Leucocytes. They are also known as White Blood Cells (WBC)as they are colourless due to the lack of haemoglobin. They are nucleated and are relatively lesser in number which averages 6000-8000
mrn^-3of blood. Leucocytes are generally short lived. There are two main categories of WBCs:
1. Granulocytes, e.g., neutrophils, eosinophils and basophils
2. Agranulocytes. e.g., Lymphocytes and monocytes.
1. Neutrophils are the most abundant cells (60-65 per cent) of the total WBCs and basophils are the least (0.5-1 per cent) among them. Neutrophils and monocytes (6-8 per cent) are phagocytic cells which destroy foreign organisms entering the body.
2. Basophils secrete histamine, serotonin, heparin, etc., and are involved in inflammatory reactions.
3. Eosinophils (2-3 per cent) resist infections and are also associated with allergic reactions.
4. Lymphocytes (20-25 per cent) are of two major types - 'B' and 'T' forms. Both B and T lymphocytes are responsible for immune responses of the body.
(c) Structure of Heart. The heart is a muscular organ. It consists four chambers which are as follows:
1. Right Auricle
2. Left Auricle
3. Right Ventricle
4. Left Ventricle
Apart from these four chambers, the heart consists valves at junctions of auricles and ventricles and at junctions of right ventricle and pulmonary artery. These valves allow unidirectional flow of blood.

Cardiac Cycle. The rhythmic contraction and dilatation of different parts of heart in one beat is called cardiac cycle.
Cardiac Output. The heart beats 72 times per minute, i.e., that many cardiac cycles are performed per minute. From this, it could be deduced that the duration of a cardiac cycle is 0.8 seconds. During a cardiac cycle, each ventricle pumps out approximately 70 mL of blood which is called the stroke volume. The stroke volume multiplied by the heart rate (no. of beats per min.) gives the cardiac output. 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.

Differences between right ventricle and left ventricle

(i) Bone marrow.
(ii) Sinoatrial node (SA node).
(iii) Reptiles have three-chambered heart except crocodile, which has four-chambered heart.

Chemical events that takes place from a blood clot are as follows
(i) When blood comes out of a blood vessel in case of injury the platelets clump together, break and release platelet factors, thromboplastin.
(ii) The enzyme thrombokinase initiates the conversion of prothrombin into thrombin.
(iii) Thrombin thus, catalysis the conversion of fibrinogen into fibrin which forms a mesh/network in which blood cells get entangled.
(iv) Ca²⁺ ions are necessary for both the above steps

Rh-antigen is present on the surface of erythrocytes in about 80-85% of the human beings. The individuals, who possess this antigen are called Rh⁺ (Rh positive) and those, who do not have it are called Rh^- (Rh negative). A person when exposed to Rh⁺ blood, develops anti Rh-antibodies. A pregnant women who is Rh^-, if bears an Rh⁺ foetus, will develop anti-Rh-antibodies during the first delivery, when the foetal blood comes in contact with her blood. These antibodies linger in the blood for sufficiently longer periods. If she carries a second foetus, that is Rh⁺, the anti-Rh-antibodies in her blood enter the foetal circulation and cause damage to the foetal RBCs. This, could become fatal. This condition is called erythroblastosis foetalis.

The mammals have no renal portal system due to the following facts
(i) It is an evolutionary trend that fishes and amphibians have well-developed renal portal system, while, in reptiles and birds this system gets reduced. Finally the mammals it ultimetely disappears.
(ii) The heart of mammals is four-chambered, due to which there is a total separation of oxygenated and deoxygenated blood.
(iii) Posterior portion of the body gets oxygenated blood from the heart and after oxidation process, etc., the blood does not contain so much impurities that it should go to the kidneys for filtration.

A unique vascular connection exists between the digestive tract and liver called hepatic poratal system.The hepatic portal vein carries blood from intestine to the liver before it is delivered to the systemic circulation.This ensures that the liver, which has the metabolic versatility to interconvert various organic molecules has first access to nutrients after the food is digested.