Blood is a fluid which flows all through the body in blood vessels.

Blood composition[edit | edit source]

Blood is composed of four main parts - blood plasma, platelets (thrombocytes), red blood cells (erythrocytes), and white blood cells (leukocytes).

The red blood cell's function is predominantly for transport of oxygen, as it contains haemoglobin (a protein with that has high proportion of iron), with which it can carry oxygen (in the form of oxyhaemoglobin). Other substances such as glucose are also carried within the blood.

White blood cells (phagocytes and lymphocytes) are part of the immune system - they help you fight against infection. If they detect an unfamiliar antigen they will attack and destroy it.

Platelets help in clotting for example when you cut yourself.

The blood is pumped by the heart, and follows a double circulatory system in humans. In mammals, the blood is red when oxygenated due to the haemoglobin.

Oxygenated and deoxygenated blood[edit | edit source]

Oxygenated means that the haemoglobin of the erythrocyte has been oxidised to form Oxyheamoglobin, deoxygenated means it hasn't reacted. Oxygenated blood in found in the pulmonary vein and aorta; deoxygenated blood is found in the pulmonary artery and the vena cava.

Blood clotting[edit | edit source]

Platelets begin this reaction. They are usually unreactive when in the smoothness of the artery or vein wall. When this smoothness is interrupted they get stuck inside it causing a very complex cascade reaction; but in short the enzyme thombronin reduces soluble fibrinogen into insoluble fibourous fibrin which forms a clot.

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