2.5 Explain the process by which the body maintains haemostasis

Haemostasis is normal blood clotting process that prevents excessive blood loss in the body following vascular injury. It is essential for survival. There are three primary mechanisms to control bleeding. The mechanisms are vascular spasm, platelet plug, and blood clotting.

Vascular spasm occurs When a blood vessels is punctured. The smooth muscles surrounding the blood vessel hold the blood supply to the area. It can hold for minutes to hours.

Platelet plug formation is a more complex process than vascular spasm. There are three phases in this mechanism: Platelet adhesion, Platelet release reaction and Platelet aggregation. Platelet adhesion is the first phase. When the damage to a blood vessel has been detected by platelets, it begins to adhere to the exposed surfaces. Once platelets stuck to a damaged area, the platelets begin to change, which is called Platelet release reaction phase.

Firstly Platelet created extensions in order to contact each other, so that they can release their contents. There are two types of chemical packages known as granules, which are held within the cytoplasm of platelets. Two types of granules are alpha granules and dense granules. Alpha granules contain clotting factors, growth factors, and fibroblasts. Dense granules contain ADP, ATP, Calcium ions, and Serotonin. In the Platelet aggregation phase, the ADP make the nearby platelets sticky and combine together with the other recruited platelets and form a platelet plug helping to stop the loss of blood through holes in small vessels.

Blood Clotting or Coagulation is the most complex haemostatic process. The main purpose of the process is to turn liquid blood into a gel. The gel is called a clot and is composed of protein fibres called fibrin in which the formed elements of blood are trapped. The gel effectively forms a cap over a wound. There are several substances in clotting process, which are called clotting factors. These factors are one to three, using Roman numerals.

These clotting factors are a cascade of interactions and resulting in clot formation. Clotting occurs in three stages. The first stage occurs via two distinct pathways, intrinsic or extrinsic, results in the formation of the enzyme prothrombinase. In the second stage of the process, prothrombin is catalysed by prothrombinase and calcium ions to the enzyme thrombin. In stage three, thrombin converts fibrinogen to loose fibrin threads.  Vitamin K is a key factor required for the formation of several clotting factors.

The clot caps a damaged area to stop the bleeding. In addition, the fibrin within the clot sews the damaged area pulling back together. Once the damage has been repaired, tissue repair take place.

Once the damaged vessels have been repaired, the fibrinolytic system prevents clots from getting too large and helps to dissolves clots. Fibrinolysis is the process of dissolving a clot, by removing the fibrin within it.

Haemostasis process is very sophisticated mechanism to protect from the loss of blood from ruptured blood vessels. However, if there is large ruptures occur on the blood vessels, medical treatment is necessary to prevent the excessive loss of blood.