Which Coagulation factor is not present in Serum?
Ans. A. Factor II. (Ref. Ganong 23rd / Table 32-5).Serum has essentially the same composition as plasma, except that its fibrinogen and clotting factors II, V, and VIII have been removed and it has a higher serotonin content due to breakdown of platelets during clotting.Guyton & Hall's Textbook of Medical Physiology 11th/pg. 463.........."Within a few minutes after a clot is formed, it begins to contract and usually expresses most of the fluid from the clot within 20 to 60 minutes. The fluid expressed is called serum because all its fibrinogen and most of the other clotting factors have been removed; in this way, serum differs from plasma. Serum cannot clot because it lacks these factors. Platelets are necessary for clot retraction to occur. Therefore, failure of clot retraction is an indication that the number of platelets in the circulating blood might be low."Additional educational point:# Tissue factor initiates the extrinsic pathway, whereas contact of Factor XII and platelets with collagen in the vascular wall initiates the intrinsic pathway.# An especially important difference between the extrinsic and intrinsic pathways is that the extrinsic pathway can be explosive; once initiated, its speed of completion to the final clot is limited only by the amount of tissue factor released from the traumatized tissues and by the quantities of Factors X, VII, and V in the blood. With severe tissue trauma, clotting can occur in as little as 15 seconds. The intrinsic pathway is much slower to proceed, usually requiring 1 to 6 minutes to cause clotting.
II
IV
X
VII
Heart, Circulation, and Blood