Body Fluids and Circulation Test - 59

Out of all other leucocytes, the neutrophils (60-65%) are most abundant and the least are basophils (0.5-1%). Platelets are cell fragments produced from megakaryocytes. During the blood clotting, the enzyme thrombin converts inactive fibrinogens into active fibrins.. 

The number of RBCs  in humans ranges from 4.2 million per mm$$^3$$ to about 5.5 million per mm$$^3$$, while the number of WBCs range from 4000 to 10,000 per mm$$^3$$. Erythrocytes are the most abundant of all the cells in the blood.

The RBC membrane contains either antigen A or antigen B, or both Antigen A and B or no antigen at all, accordingly the blood is classified as blood group A , B , AB and O respectively. The blood plasma of blood group A will have antibodies for B, that of B will have antibodies for A,  that of AB will have non, while that of O will have both the antibodies. If blood is transfused at random this will lead to antigen-antibody reaction - like if A is the blood group of the recipient while the blood group of the donor happens to be B, this will lead to clumping of the RBCs.

Lymphocytes are the smallest leukocytes with a rounded nucleus. They flow through the lymphatic system or fluid and are of 2 types-  B-Lymphocytes and T-lymphocytes and defend the body against pathogens and infections.

Ca$${+2}$$ is necessary for blood coagulation -

Lymph has a pale yellow colour due to absence of RBCs and platelets,  it has abundance of WBCs, Lymphocytes, carbohydrates, proteins, fats and nitrogenous waste.

Option A. A - Thromboplastin, B - Prothrombinase, C - Thrombin, D – Fibrinogen

Reason: In the following diagram, the process of blood clotting. In the first step at the site of an injury, the blood platelets disintegrate and release a phospholipid, called platelet factor-3. Injured tissues also release a lipoprotein factor called thromboplastin. These two factors combine with calcium ions and certain proteins of blood plasma to form an enzyme called prothrombinase. In the second step, prothrombinase inactivates heparin in the presence of calcium. Prothrombinase catalyzes the breakdown of prothrombin into an active protein called thrombin. In the third step, thrombin acts as an enzyme and first brings about depolymerization of fibrinogen into its monomers. Later thrombin stimulates repolymerization of these monomers into long insoluble fiber-like polymers called fibrin.

In the blood coagulation pathway thrombin activates Factor XIII to XIIIa that helps in binding of fibrin monomers to form the stable fibrin filament.

B. Atrium relaxes

Reason: During a heartbeat there is contraction and relaxation of atria and ventricles. The contraction phase is called the systole while the relaxation phase is called the diastole. Atrial diastole is characterized by the relaxation of the atrial muscles. During this stage, the blood enters into the atria, as the volume of the blood in the atria increases the pressure within it decreases.