Atherosclerosis is the coronary artery disease caused due to the narrowing of the lumen of arteries. The narrowing of arteries occurs due to deposition of calcium, fat, cholesterol and fibrous tissue affecting vessels that supply blood to the heart muscles.

(a) Purkinje fibres are the impulse conducting fibres which relay the contraction impulses from AV node into the walls of ventricles.

(b) Bundle of His are mass of specialised fibres that originates from the AV node.

(a) Fibrinogens are inactive components of blood plasma. Under the action of enzyme thrombin they form a clot or coagulum of a network of threads called fibrin in which dead and damaged elements of blood are trapped.

(b) Globulins are primarily involved in immunity, i.e., defence mechanisms of the body.

(c) Neutrophils are phagocytic cells which destroy foreign organisms entering the body.

(d) Lymphocytes are specialised cells which are responsible for the immune responses in the body. Two major types of lymphocytes, that are involved in this process are B and T-lymphocytes.

A protein named as rhesus antigen, is present on the surface of red blood corpuscles. The population having this protein are called $\mathbf{R h}$ positive $\left(\mathrm{Rh}^{+}\right)$while others who do not have this protein are known as Rh negative ( $\mathrm{Rh}^{-}$) (dominant). Erythroblastosis Foetalis occurs due to Rh incompatibility between the foetus and mother during pregnancy. Rh antigen of the foetus do not get exposed to the $\mathrm{Rh}^{-}$blood of the mother in the first pregnancy. However, during the delivery of the first child, there is a possibility of exposure of the maternal blood to small amounts of the $\mathrm{Rh}^{+}$blood from the foetus. In such cases, the mother starts preparing antibodies against Rh antigen in her blood and during her subsequent pregnancies the Rh antibodies from the mother ( $R h$ - ve) leak into the blood of the foetus ( $\mathrm{Rh}+\mathrm{ve}$ ) resulting in the destruction of foetal RBCs. This could be fatal to the foetus or could cause severe anaemia and jaundice, even may lead to the death of the foetus.

Blood exhibits coagulation or clotting in response to an injury or trauma. Coagulation prevents excessive loss of blood from the body. In its absence their could be huge loss of blood, which can be fatal.