THROMBOSIS

THROMBOSIS

   Thrombosis is the process of formation of solid mass in circulation from the constituents of flowing blood, the mass itself is called thrombus.

NOTE-

   Hemostatic plughs are the blood clot formed in healthy individual at the site of bleeding. It is helpful as they stop the escape of blood and plasma. Where as thrombi developed in the unruptured cardiovascular system may be life threatening by causing one of the following harmful effect-

1. Ischemic injury:-

     Thrombi may decrease the blood supply to part of an organ or tissue and cause ischemia which may subsequently resulting in infraction.

2. Thrombo embolism:-

  The thrombus or its part may get dislodged and be carried along in the blood stream as embolus to lodge in a distant vessel.

Pathophysiology:_

  The factor which predisposes to thrombus formation are-

1. Endothelial injury

2. Altered blood flow

3. Hyper coagulability of blood 

   These events are described as-

1. Endothelial injury-

    The integrity of blood vessel wall is important for maintaining normal blood flow.

Number of factors and condition may cause vascular injury and predispose to the formation of thrombi.

 These are as under -

i. Endocardial injury in myocardial infraction, myocarditis

ii. Ulcerated plaques in advance atheroscalrosis 

iii. Hemodynamic stress in hypertension 

iv. Arterial diseases

v. Diabetes mellitus

2. Role of platelets :-

   Platelets comes to play a central role in normal hemostasis as well as thrombosis. 

The sequence of events is as under-

i. Platelets adhesion:-

  The platelets in circulation recognize the site of endothelium injury and adhere to exposed subendothelium collagen.

ii. Platelets release reaction:-

  The activated platelets then undergo release reaction by which the platelets granules are released to the exterior.

iii. Platelets aggrigation:-

  This result in formation of temporary hemostatic plough. 

3. Role of coagulation system:-

  Coagulation mechanism is the conversion of the plasma fibrinogen into solid mall of fibrin. The coagulation system is involved in both hemostatic process and thrombus formation. 

4. Alteration of blood flow:-

  Turbulence and stasis occur in thrombosis.

5. Hyper coagulability of blood:-

   The effect of hypercoagulability on thrombosis is formed by advance age, smoking and obesity.

6. Predisposing factor:-

   The number of primary and secondary factors favour thrombosis.

i. Primary factor-

   a. Deficiency of antithrombin

   b. Defect in fibrinolysis

ii. Secondary factor-

   a. Cigarette smoking

   b. Immobilization 

   c. Prolonged bed rest

Origin of thrombi:-

    Thrombi may arise from the heart, arteries, veins or in micro circulation.

1. Cardiac thrombi:-

  Thrombi may form in any of the chambers of the heart and on the valcusps.

2. Arterial and venous thrombi:-

  Arterial thrombi-  Arota, coronary arteries, arteries of limbs, renal artery, cerebral artery

Venous thrombi-  veins of lower limb, pulmonary veins renal vein

 Capillary thrombi- minute thrombi composed mainly of packed red cell are formed in the capillary in acute inflammatory lesions.

Fate of thrombus:-

  The possible fate of thrombi can be as under-

1. Resolution:-

  Thrombus activates the fibrinolytic system with consequent release of plasmin which may dissolve the thrombus completely resulting in resolution.

2. Organization:-

  If the thrombus is not remove, its start getting organized. Fibrocytic cells appear and begin to phagocytes fibrin and cell debris.

Proteinetic enzyme liberated by lucocytes and endothelial cell start digesting coagulent.

Capillaries grown into the thrombus from the site of its attachment and fibroblast start invating the thrombus.

3. Propogation:-

    The thrombus may enlarge in size due to more and more deposition from the constituents flowing blood. In this way, it may ultimately cause obstruction of some important vessels.

4. Thrombo embolism:-

  The thrombi in early stage and infected thrombi are quite friable and may get detached from its vessel wall. These are released in part or completely in blood stream as emboli which produces in effect at the site of there lodged.