The Blood Coagulation Process
Coagulation can be initiated by either of two distinct pathways.
Regardless of whether the Extrinsic or Intrinsic pathway starts coagulation, completion of the process follows a common pathway. The common pathway involves the activation of factors: X, V, II, XIII and I. Both pathways are required for normal hemostasis and there are positive feedback loops between the two pathways that amplify reactions to produce enough fibrin to form a lifesaving plug. Deficiencies or abnormalities in any one factor can slow the overall process, increasing the risk of hemorrhage.
The coagulation factors are numbered in the order of their discovery. There are 13 numerals but only 12 factors. Factor VI was subsequently found to be part of another factor. The following are coagulation factors and their common names:
The liver must be able to use Vitamin K to produce Factors II, VII, IX, and X. Dietary vitamin K is widely available from plant and animal sources. It is also produced by normal intestinal flora. A deficiency is rare but may occur:
At birth and throughout childhood, Factor VIII levels are the same as adult values. Many other factor levels are below adult levels at birth, some as low as 10% of adult levels. Theses levels increase toward the adult levels by age 6 months, although they may remain mildly below adult normal range throughout childhood. Despite lower levels, newborns and children do not normally experience bleeding. This confers some level of antithrombolic protection in youth. During pregnancy Factor XI can decrease, but fibrinogen and factor VIII increase.
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