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Blood is a major part of the human body. It is required for most functions of cells. Blood is comprised of 3 main sections: Plasma, Thrombocytes, red blood cell (Erythrocytes), White Blood Cells (Leukocytes).




Plasma contains many molecules ranging from clotting factors, dissolved proteins and even carbon dioxide through respiration. Plasma is extremely important in the transport of metabolites such as ATP an glucose around the body. It also can contain waste molecules such as urea and lactic acid.


Thrombocytes are used in the clotting process and used to clog a broken seal with the aid of clotting factors via the Intrinsic pathway.


Erythrocytes are used in gas exchange using the protein Haemoglobin (Hb). The most distinct characteristic of the Erythrocytes is their unique biconcave shape. To be more specific, erythrocytes are flat and disc-shaped with indentations in the middle of both sides. This contribute to the ease of carrying and transporting oxygen across the whole blood stream. Erythrocytes are also able to demonstrate their membrane flexibility by  being able to squeeze through the very tiny and narrow blood capillaries[1].


Leukocytes are used to defend the body against pathogens via phagocytosis or antibody production. There are many leukocytes differing in their mechanisms and appearance (granular/agranular): lymphocytes, monocytes, basophils and eosinophils.

Blood Pressure

Blood pressure is the pressure of the blood vessels exerted by circulating blood. It is normally measured at upper arm using a sphygmomanometer. During a heartbeat, there are two types of blood pressure is measured. One is 'upper' systolic pressure (contraction) and another is 'lower' diastolic (relaxation) pressure. Normal blood pressure for a healthy person is 120/80 mmHg (systolic/diastolic).

Blood Group Systems

There are 30 blood groups systems recognised by International Society of Blood Transfusion. The major blood group systems are ABO Blood Group System and Rh Blood Group System.


  1. Sherwood (2010) Human Physiology (From Cells to Systems), 7th edition, Canada : BROOKS/COLE CENGAGE Learning. page 392-4

External Links

  1. ISBT. International Society of Blood Transfusion.
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