Blood has many functions including transportation of nutrients round the body, maintaining homeostasis and the imune system. It is made up of plasma, red blood cells, white blood cells and platelets.

Functions of blood

  • Transportation: The blood carries other substances around the body inside Arteries, Veins and Capillaries. These include gasses (Oxygen and Carbon Dioxide), waste products (water, urea), hormones, enzymes and nutrients (glucose, amino acids, vitamins and minerals). The blood flows through the Circulatory System.
  • Maintaining Homeostasis: Altering the blood flow to the skin can help to reduce body temperature. Transportation of enzymes which are used to maintain our internal environments.
  • Immunity and defence: White blood cells fight infection and platelets help repair damage and clot the blood

Constituents of blood

Blood is made up of a number of types of cells:

  • Plasma: Plasma is a straw-coloured fluid in which blood cells are suspended. It is made up of approximately 90% water as well as electrolytes such as sodium and potassium and proteins.
  • Red Blood Cells (Erythrocytes): The main function of red blood cells is to carry oxygen. RBC's contain a protein called Haemoglobin. This combines with oxygen to form Oxyhaemoglobin. Each RBC has a lifespan of approximately 120 days before it gets broken down by the spleen. New RBC's are manufactured in the bone marrow of most bones. There are approximately 4.5-5 million RBC's per micro-litre of blood.
  • White Blood Cells (Leucocytes): There a number of types of white blood cells, although the function of all of them is to help fight disease and infection. They typically have a lifespan of a few days and there are only 5-10 thousand WBC's per micro-litre of blood.
  • Platelets (Thrombocytes): Platelets are disc shaped cell fragments which are involved in clotting the blood to prevent the excess loss of body fluids.

Circulatory System:

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