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Blood is a major part of the human body; it allows 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).There are three types of blood. Platelets help the blood to clot. Clotting stops the blood from flowing out of the body when a vein or artery is broken. Red blood cells carry oxygen. White blood cells ward off infection.




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, proteins (albumin being the most abundant plasma protein), carbon dioxide and oxygen (from respiration) and antibodies of the immune system. Plasma 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 (red blood cells) 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 contributes to the ability to carry and transports oxygen across the entire bloodstream. 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 female is usually 37-47%, this is a quick and cheap method of testing blood health[2].The normal ranges of Erythrocytes are 4.7 to 6.1 million cells per microlitre of blood for men and 4.2 – 5.4 million cells per microlitre of blood for women[3]..


Leukocytes (white blood cells) 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.The normal range of leukocytes in the blood is 5000 to 10,000 cells per microlitre for men and 4500 – 11,000 cells per microlitre of blood for women[4].

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 the International Society of Blood Transfusion. The major blood group systems are ABO Blood Group System and Rh Blood Group System. The four types of blood in the ABO Blood Group System are 0(I), A(II), B(III) and AB(IV) and the two types of Rh in the Rh Blood Group System are Rh+ and Rh-. 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
  3. Anaemia

External Links

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


  1. Sherwood (2010) Human Physiology (From Cells to Systems), 7th edition, Canada: BROOKS/COLE CENGAGE Learning. page 392-4
  2. Silverthorn (2013) Human Physiology: Pearson New International Edition: An Integrated Approach: 6th edition: page 543
  3. Leukemia and Lymphoma society. Understanding blood counts. No date. [cited 06/12/2018]. Available from:
  4. Leukemia and Lymphoma society. Understanding blood counts. No date. [cited 06/12/2018]. Available from:
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