report 代写 The Cardiovascular System Description Biology Essay

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Explain the process by which the body maintains haemostasis.

Haemostasis is the body's reaction to stop the loss of blood exiting the body from damaged blood vessels. There are three main steps to haemostasis, vascular spasm, Platelet Plug and coagulation:

Vascular spasm

When a broken blood vessel occurs, the first reaction in Haemostasis to stem the flow of blood is a vascular spasm. Pain receptors stimulate platelets to secrete vasoconstrictor "Serotonin" which cause the blood vessels to constrict reducing the blood flow this allows for time for the next stage of the haemostasis process.

Platelet Plug

Platelets in their normal state flow freely in the blood plasma as the lining of the blood vessel is smooth and coated with a platelet repellent prostacyclin. When the blood vessel is damaged, or broken, platelets are exposed to collagen fibres that are present in the walls of the arterioles, platelets become tacky and start sticking together and react with proteins in the blood plasma to form a temporary "plug" until a more permanent fix occurs in the form of coagulation.


Thromboplastin protein reacts with vitamin K and Ca2+ Ions. The Thromboplastin then activates with the inactive prothrombin protein. The protein fibrinogen that is normally inactive becomes fibrin which is a fibrous compound. The fibrin starts to form a "net" across the damages vessel and platelets become trapped in the net to form permanent "glue" fixing the damages vessel to prevent blood loss and bacteria from entering the wound.


Explain the different blood groups A, B, O and Rhesus

State which groups are compatible, and explain why.

Your "new recruits" now require an explanation of the above. Present this to them in a clear brief manner. Group compatibility may be best shown by use of a table. Ensure that your explanation is written in your own words and give an example of the consequences of group incompatibility.