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Blood and blood clotting process

Blood clotting process hemostasis- when we get a cut anywhere on our body, then blood starts coming out, platelets present in the blood produce a mash of fine threads that trap the red blood cells forming a clot that blocks the cut and stops bleeding. Hemostasis is the opposite of hemorrhage.

Blood coagulation factors:

Haemostasis has 3 steps, they are

Stage of blood clotting:

  1. Vasoconstriction,
  2. temporary blockage of a break by a platelet plug,
  3. blood coagulation.

Blood clotting mechanism:

All Vertebrates include Human beings, have developed a mechanism for preventing the accidental loss of blood. Whenever a blood vessel is ruptured, one of the soluble plasma proteins, fibrinogen, is enzymatically converted into an insoluble protein, fibrin, which forms a semi-solid clot.

Blood clotting facts:

Some people think that blood clots when it becomes exposed to the air or when it stops flowing.
However, if one were to carefully remove blood from a vessel- without allowing it to contact the damaged part of the vessel, and then place this blood on a smooth plastic dish or one lined with paraffin, it would not clot.

However, if this blood were allowed to touch any damaged tissues or were placed on glass or some other relatively rough surface, the blood would clot.

Blood clotting factor:

Either the damaged tissues or the blood itself must release some chemical that initiates the clotting
mechanism. Actually, it is both damaged tissues and disintegrated platelets in the plasma that release substances responsible for the clotting reaction. Platelets are very small disc-shaped bodies found in mammalian blood and formed in the bone marrow from large cells called megakaryocytes. Platelets seem to disintegrate more readily upon contacting glass surfaces than on plastic surfaces. Platelets are also called thrombocytes.

Blood clotting mechanism:

When a blood vessel is cut, the damaged tissues release a lipoprotein, called thromboplastin, which initiates the clotting mechanism. Calcium ions and certain protein factors in the plasma must be present in order for thrombo­plastin to be effective. Thromboplastin interacts with Ca+2 and these proteins to produce prothrombinase, the enzyme that catalyzes the second step in the clotting mechanism. Prothrombinase can also be made by the interaction of a substance released from the disintegrated platelets (platelet factor # 3) and other factors in the plasma, including Ca2+ and proteins. The prothrombinase made from either the tissues or the platelets catalyzes the conversion of prothrombin, a plasma globulin into thrombin. Finally, thrombin enzymatically converts fibrinogen into fibrin, an insoluble protein. Fibrin forms long fibers that mesh and trap red cells, white cells, and platelets, forming the clot. Usually the clot forms within 5 minutes of the rupturing of the vessel. The clot then begins to contract and squeeze out most of the plasma from itself within an hour. This process, called clot retraction, serves to increase the strength of the clot and also pulls the vessel walls adhering to the clot closer together.

The extruded plasma is now called serum since all the fibrinogen and most other clotting factors have been removed. Because it lacks these constituents, the serum cannot clot.

Hemostatic drugs:

The drugs which are used to control the oozing of blood from the injured blood vessels are called hemostatic. Such as thrombin NF,  thromboplastin, fibrinogen, oxidized cellulose.

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