Chemical composition of blood
Blood is a liquid connective tissue made of plasma and formed elements (erythrocytes, leukocytes, platelets). About 90% of plasma is water; the rest is proteins (about 7%), fats, carbohydrates and mineral salts, and its composition is kept constant. Blood cells are mainly made in the red bone marrow in the spongy part of bones. Platelets are small blood plates without a nucleus (cell fragments) that take part in clotting. When a vessel is damaged, platelets break and release a substance that converts plasma prothrombin to thrombin; thrombin turns soluble fibrinogen into insoluble fibrin threads, to which blood cells stick, forming a clot (thrombus) that seals the wound. Calcium salts are needed; in a healthy person bleeding from a small cut stops in a few minutes. Disturbed clotting – haemophilia – is inherited; even a small wound can bleed heavily, so medical supervision is required.
Draw the clotting chain with arrows: vessel damage → platelets break → prothrombin → thrombin → fibrinogen → fibrin → clot. Quiz a friend on the order.