TRANSPORT IN MAMMALS PART 6: THE FUNCTION OF BLOOD

The blood has two important functions: the transport function and the protective function.

THE TRANSPORT FUNCTION OF BLOOD
Blood acts as a transport medium carrying various substances from one part of the body to another. The blood transport the following:

• Digested food nutrients from the ileum to all parts of the body (via plasma).
• Excretory products from the tissues to the excretory organs for removal (via plasma).
• Hormones, from the endocrine glands to the target organs (via plasma).
• Heat, from the respiring tissues to other parts of the body, hence maintaining constant body temperature (via plasma).
• Oxygen, from the lungs to all parts of the body (via the red blood cells).

THE PROTECTIVE FUNCTION OF BLOOD

• Phagocytosis by the phagocytes: The phagocytes engulf and ingest foreign particles (mainly bacteria) at the site of the wound or cut. Some of the phagocytes are killed in the process. These dead phagocytes at wound, together with the dead foreign particles, form pus.
• Production of antibodies by the lymphocytes: The production is triggered when foreign particles produce toxins. The antibodies neutralise the poisonous effect of the toxins. The antibodies can also kill the foreign particles by causing the foreign particles to clump together (agglutination). The agglutinated bacteria are then ingested by the phagocytes.
• Blood clotting: This seals wound, prevents entry of foreign particles and prevents excessive loss of blood.

IMPORTANT:

• In the lungs, haemoglobin in the red blood cell combines loosely with oxygen to form oxyhaemoglobin.
• The blood containing oxyhaemoglobin is called OXYGENATED BLOOD.
• The oxyhaemoglobin is then transported to all body tissues.
• The oxyhaemoglobin then releases its oxygen as the blood passes through tissues containing very little oxygen.
• The blood containing little oxygen is called DEOXYGENATED BLOOD.
• The deoxygenated blood is then transported back to the lungs

OXYGENATED BLOOD TENDS TO BE BRIGHT RED IN COLOUR WHEREAS DEOXYGENATED BLOOD TENDS TO BE BLUISH. HENCE ARTERIES WHICH GENERALLY TRANSPORT OXYGENATED BLOOD IS RED IN COLOUR WHILE THE VEINS WHICH GENERALLY TRANSPORT DEOXYGENATED BLOOD IS BLUISH IN COLOUR.