Blood flows uninterruptedly through the branching vessels of the body. When the walls of these blood vessels break, the body sets in motion hemostasis which stops the exodus of blood and blood components outside the vessels.
The body is quick to react to signs of bleeding within the body. Hemostasis response if usually fast, localized and is carefully controlled. It employs the used of many blood coagulation factors normally present in the plasma. Additionally, platelets and other injured tissue cells release substances that trigger the hemostasis mechanism to set in motion. The aim of hemostasis is for fibrous tissue to grow into clots and be able to seal the gap or hole found in the blood vessel.
The body first reacts to signs of blood vessel damage by constricting the damaged part. With vasoconstriction in place, blood flow to the area is minimal, thereby presenting a momentary solution to the problem. Various factors can trigger vasoconstriction which may include chemicals released by platelets and endothelial cells, reflexes by local receptors and injury to vascular smooth muscles.
The quality of vascular spasm is directly proportional to the amount of tissue damage. A window time of about 20-30 minutes is given by this constricting action, thus giving the body ample time to prepare and initiate its response and necessary action in closing the injured part.
Platelet Plug Formation
The platelets are the ones responsible for creating a temporary seal that plugs the break in vessel walls. A key role is being played by the platelets as it sets the stage for events that lead to the formation of blood clot.
When the blood vessels are not damaged, the platelets do not stick to the endothelial linings of the blood vessels. However, when the vessel walls are damaged and the collagen fibers are exposed, the platelets become excited and with the help of the von Willebrand Factor, they adhere tenaciously to the fibers and become very sticky.
As the platelets attach, they release serotonin that further enhances vasoconstriction. They also release adenosine diphosphate that attracts more platelets. Once the platelet plug is formed, the stage is set for the last part of hemostasis.
Coagulation is another term for blood clotting. During blood clotting, the liquid blood is transformed into a gel, which leads to three critical three phases. During the coagulation process, prothrombin activator is formed. With the help of prothrombin activator, prothrombin is converted into thrombin. The resulting thrombin then jumpstarts the joining of the molecules fibrinogen found in the plasma to form a fibrin mesh. This fibrin mesh then traps blood cells, sealing the hole until the time when the damaged vessels will be repaired permanently.
The coagulation process is very complicated. It involves over 30 substances in order to effectively seal a damaged blood vessel. Several factors enhance blood clotting and it includes procoagulants or clotting factors. Vitamin K, which is not directly involved in the process of coagulation, is instrumental for the making of four clotting factors.