Tag: defence against infectious disease

Platelets are parts of the blood that help the blood clot. They are smaller than red or white blood cells. Platelets are a natural source of growth factors. They circulate in the blood of mammals and are involved in hemostasis, leading to the formation of blood clots. Platelets release thread-like fibers to form these clots. 

Blood clotting is the process by which blood changes from liquid to gel and stop bleeding. When the blood vessels get injured, platelets in blood produces prothrombin in the presence of vitamin K. The prothrombin then converts into the thrombin (active form) in the presence of thrombokinase and calcium ions. This thrombin then converts fibrinogen (inactive) into the fibrin (active). Fibrin thread then plugs the damaged part and appear like a clot. Thus, the correct answer is option A.

Platelet, also called thrombocyte, colourless, nonnucleated blood component that is important in the formation of blood clots (coagulation). Platelets are found only in the blood of mammals.

Only mammals have platelets, tiny cells without nuclei that are responsible for plugging the leaks in the blood vessels. Other animals use more conventional systems of hemostasis. Some marine invertebrates have a single type of blood cell, responsible for hemostasis, but also for other types of defences. Non-mammalian vertebrates have specialized nucleated thrombocytes to do the job.

Platelets are small, non-nucleated cells that are derived from megakaryocytes in the bone marrow. Platelets circulate in the blood, sense damage to a blood vessel and accumulate at these sites, where they initiate blood clotting. They are fragments of cytoplasm that are derived from the megakaryocytes of the bone marrow.

Only mammals have Platelets. Non-mammals possess thrombocytes which are nucleated cells which have been shown to have a haemostatic function paralleling that of mammalian platelets.

A megakaryocyte is a large bone marrow cell with a lobated nucleus responsible for the production of blood thrombocytes (platelets), which are necessary for normal blood clotting.

The ornithine cycle (urea cycle) is a metabolic pathway that converts toxic ammonia into urea, which is then excreted by the kidneys.