Disorders of Haemostasis
Lec. 9 26 Nov, 2017Prof.Dr.Baybeen Al-Selevany
Objectives
Bleeding Disorders
Clotting Disorders
Defect in the hemostatic mechanisms i.e. imbalance between clotting and anticlotting systems.
Bleeding disorder: lead to prolongation of bleeding and bleeding time.
Clotting disorder: Abnormal activation of clotting system which is lead to clot formations and prolongation of clotting time.
1. Bleeding disorders
Excessive bleeding can result from deficiency of any one the following factors:
1. Deficiency of clotting factors. For example in Hemophilia bleeding is due to absence of antihemophilic factors and clotting time is prolonged.
3 types:
Hemophilia A: due to lack of antihaemophilic factor A (i.e. factor VIII). Is the most common of all inherited coagulation disorders, as it comprises about 85% of all cases of hemophilia. This type of hemophilia is also called classic hemophilic. It is X-linked inherited disease. Severe bleeding is common in males. Treatment: includes replacement therapy with factor VIII.
Hemophilia B: occurs a result of a deficiency of factor IX. It is also known as “Christmas disease” and accounts for approximately 10% of all hemophilia's. It is also X-linked recessive trait.
Treatment: replacement therapy with factor IX.
Hemophilia C: The least common of three major types of hemophilia. Caused by deficiency of factor XI & accounts less than 5% of all hemophilia. It is inherited disease. Hemophilia C is also known as "Rosenthal syndrome."Treatment: replacement therapy with factor XI.
In all types of hemophilia bleeding usually does not occur except after trauma. Bleeding can last for weeks after extraction of a tooth. Bleeding may occur into the muscles & may result into hematomas. Bleeding in hemophilia is usually from larger vessels.
2. Deficiency of platelets (Thrombocytopenia): Thrombocytopenia: means the presence of a very low quantity of platelets in the circulatory system, resulting in chronic bleeding through small capillaries & venules. Bleeding does not occur until the number of platelets in the blood falls below 50,000/ml. Levels as low as 10,000/ml is lethal. The skin of such a person displays many small, purplish blotches, giving the disease the name “Thrombocytopenia purpura”. Purpura means multiple red spots larger than petechia (multiple small red spots on the skin which result from RBC’s leaving the small blood vessel.). In thrombocytopenic purpura bleeding time is greater than normal value.
3- Vitamin K deficiency: This is required for synthesis of clotting factors in the liver.
2. Clotting Disorders
Inappropriate of clotting mechanisms in intact blood vessels results in fibrin clot formation, a phenomenon known as intravascular thrombosis. Thrombosis may be due to activation of clotting factors or due to lack of inhibitory factors (anticoagulants) to neutralize activated clotting factors. Once a thrombus (clot) has developed, it break away from its attachment to flow along with the blood such freely flowing clots are known as emboli. Emboli do not stop flowing until they come to a narrow point in the circulatory system. Thus, emboli that originate in large arteries or in the left side of the heart plug either smaller systemic arteries or arterioles in the brain, kidneys. Emboli that originate in the venous system and in the right side of the heart flow into the vessels of the lung to cause pulmonary arterial embolism. Blood clots (thrombosis) may form in any blood vessel but are more common in veins(venous thrombosis) than in arteries (arterial thrombosis) because blood flow more slowly through veins. Most blood clots tend to occur in the veins of the legs interfering with venous return of blood to heart. Blood clots also may result in inflammation, edema, discoloration & ulceration of the legs.
The most serious complication of venous thrombosis is pulmonary embolism, which occurs when a clot from the legs moves via the heart to the lungs, where it obstructs the pulmonary circulation. Arterial thrombosis is rather rare & is associated with large blood vessel damage. The consequences of arterial clots are more severe than venous thrombi. They may lead to myocardial infarction (heart attack); cerebral infarction (stroke), or limb infarction, which may result in gangrene.
Microcirculatory thrombosis leads to local ischemia & necrosis (cell death).