question_answer 19)

    Mark the pair of substances among the following which is essential for coagulation of blood. (a) heparin and calcium ions                                        (b) calcium ions and platelet factors (c) oxalates and citrates                                                (d) platelet factors and heparin

Answer:

                  (a) Certain factors released by the tissues at the site of injury can initiate coagulation process. Calcium ions and platelet factor act in the first step of coagulation which is as follows (i) At the site of an injury, the blood platelets disintegrate and release a phospholipid, called platelet factor 3 (platelet thromboplastin) (ii)Injured tissues also release a lipoprotein factor called thromboplastin. (iii) These two factor combine with calcium  ions and certain proteins of the blood plasma to form an enzyme called pro-thrombinase. (iv)Prothrombiminase catalyzes prothrombin into active protein called thrombin. (v) Thrombin further converts inactive fibrinogens into fibrin in the blood plasma. (vi) Then the long fibres of fibrin form a dense network upon wound and trap blood corpuscles RBCs, WBCs and platelets) to form a clot. And the other options are wrong.