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Blood is a major part of the human body, allowing cells in tissues and organs to function properly. It is pumped around the body by the heart and carried in the Cardiovascular System network of arteries, arterioles, capillaries, venules and veins. Blood components can be divided in to three section: Blood Plasma Thrombocytes and cellular components (Red Blood Cells, Erythrocytes, and White Blood Cells, Leukocytes).




Plasma is the main constituent of blood, contributing to around 52% of it's total volume. Plasma consists mainly of water, and it contains many dissolved molecules including clotting factors, proteinscarbon dioxide and oxygen (from respiration) and antibodies of the immune systemPlasma is extremely important in the transport of metabolites such as ATP and glucose around the body. It contains 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 ability to carry and transport oxygen across the entire blood stream. Erythrocytes are also able to squeeze through the narrow blood capillaries[1]. They are the most abundant cell type in blood, and they can be measured against total blood volume to give a value called the haematocrit. The expected haematocrit for a male is 40-52%, whereas a females is usually 37-47%, this is a quick and cheap method of testing blood health.[2]


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

Main article: 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

Main article: 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. If one has the blood type O, they are described as a 'universal donor' as this type of blood will be accepted by any blood type during transfusion.  

See also

  1. Haemoglobin
  2. Hypertension


  1. Sherwood (2010) Human Physiology (From Cells to Systems), 7th edition, Canada : BROOKS/COLE CENGAGE Learning. page 392-4
  2. Human Physiology: Pearson New International Edition : An Integrated Approach

External Links

  1. ISBT. International Society of Blood Transfusion.
  2. Table of blood group systems.
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