Question

Prothrombin, which helps in clotting of blood, is released by?
A) Monocytes
B) Erythrocytes
D) Lymphocytes
D) Blood platelets

Answer 1

Hint: In humans, blood oozes out from a cut or injury and forms a semi-solid or solid clump, which is called a blood clot and this process is called blood clotting. Blood clotting is necessary to prevent excessive loss of blood.

Complete answer:
Blood clotting is a cascade process which means an enzyme activates another enzyme which in turn acts as an activator for another enzyme. A total of 13 factors or enzymes are involved in the clotting of blood. Along with these factors, calcium ions also play an important role in blood clotting.

Prothrombin is present in the bloodstream in its inactive form. It is released by blood platelets and converted to its active form, thrombin, in response to an injury by an enzyme complex, thrombokinase.
Active thrombin converts inactive fibrinogen present in the blood to its active form, fibrin, which clumps together and forms a blood clot.

Let us also look at the explanation of the given options:
A) Monocytes- They are a type of agranulocytes having a large bilobed nucleus. They protect from bloodborne pathogens and also clean up dead cells.
B) Erythrocytes- These are biconcave cells lacking a nucleus. They contain an iron-rich protein called haemoglobin, which plays a role in transporting oxygen to and from various tissues and organs.
C) Lymphocytes- These white blood cells are colourless cells formed in the lymphoid tissue. They produce antibodies and play a role in the body's defence mechanism.
D) Blood platelets- These are specialised blood cells produced in the bone marrow. they play a role in blood clotting during a cut or wound.

Hence, the correct answer is option D i.e, Blood platelets.

Note: 13 factors involved in blood clotting are-
- The factor I (fibrinogen)
- Factor II (prothrombin
- Factor III (tissue thromboplastin or tissue factor)
- Factor IV (ionized calcium)
Factor V (labile factor or proaccelerin)
- Factor VI (unassigned)
- Factor VII (stable factor or proconvertin)
- Factor VIII (antihemophilic factor)
- Factor IX (plasma thromboplastin component or the Christmas factor)