Question

Blood platelets are
a. Nucleated
b. Nucleus is many lobed
c. Nucleus is very small
d. Denucleated

Answer 1

Hint: Blood contains plasma and cells. Plasma includes liquid components of the blood. Cellular part of the blood includes Red blood cells (Erythrocytes), White blood cells (leukocytes) and platelets (Thrombocytes). WBC and RBC develop from bone marrow. Megakaryocytes (large bone marrow cells) produce platelets. Platelets are not true but fragments of cells. Nucleus is the main part of the cells which also carries genetic information.

Complete answer:
Platelets are the clotting factors present in the blood. Platelets are not actually cells but these are the small fragments of cells formed by megakaryocytes that are giant cells of the bone marrow. Platelets help in the blood coagulation. It forms a fibrin clot at the site of injury which covers the wound and prevents the blood from leaking out. Platelets contain prothrombin in inactive form. It is then converted into thrombin active form. It helps in the formation of fibrin from fibrinogen which ultimately results in the clotting.

Platelets are formed as a result of fragmentation of giant megakaryocytes, which itself derived from stem cells of the bone marrow that’s why platelets lack a nucleus but they do contain other organelles such as mitochondria and endoplasmic reticulum. The process of fragmentation of megakaryocytes to platelets is known as thrombopoiesis; it occurs with the help of dominant hormones termed as thrombopoietin (TPO). One megakaryocyte cell releases about thousands of platelets.

As we have discussed above that platelets are cell fragments so they do not have any nucleus. Platelets form fibers for coagulation so they must be nucleus free so that narrow fibers can be easily formed.

Hence, the correct answer is option (D).

Note: Platelets are not true cells still they contain organelles and specific proteins which stick to breaks in the blood vessel wall and secrete other proteins. Platelets can also change their shape when they become sticky as they have similar structure as muscle proteins. Platelets are the smallest and lightest blood cell. Many types of disorders occur due to the inappropriate production of platelets. Mostly low platelets count disorder occurs in patients due to which excessive bleeding does not stop. Higher number of platelets can also cause unnecessary clotting of blood which can result in heart attacks.