A. Transportation
B. Regulation
C. Protection

A. Blood as a transport system

• Transportation of respiratory gases

Oxygen is essential for living cells. Blood taka up this gas from the lungs and transport to other cells incorporated into red cells in a substance called oxygenated-hemoglobin. Carbon dioxide is produced due to the metabolic activities of the living cells and blood helps to transport this gas to the lungs to eliminate. Carbon dioxide is transported mainly as bicarbonate dissolved in blood.

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• Transportation of Nutrients

Complex substances in our diet are digested into absorbable nutrients like glucose, amino acids, fatty acids, vitamins and minerals. These are absorbed into the blood through the gastrointestinal system and circulated throughout the body.

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• Transportation of waste products

Waste products are transported to the appropriate organs for excretion.  For example urea and ammonia are diverted into kidneys to be excreted as urine and Carbon dioxide is transported into the lungs to eliminate form the body

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• Transportation of other substances

Whatever the substance is to reach a destination within the body it needs the help of blood because blood is the transport system of the body. For example if you take a medicine either as a tablet or as an injection it enters into the blood circulation to reach the site of action. Hormones produced by endocrine glands are also released into the blood to reach their destination.

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B. Regulatory Role of Blood

Human bodies have optimal functionality only if the conditions inside the body are regulated in relatively constant and stable levels. This regulation is called homeostasis. Blood and the circulatory system are directly related to the homeostasis. Body temperature, acid base balance or pH and blood pressure are important parameters maintained within stable levels.

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C. Protective Role of Blood

Protection from micro organisms like virus, bacteria and fungi is the responsibility of the immune system. White blood cells directly engulf some of these pathogens and this process is known as phagocytosis. Immuno-globulins and antitoxins dissolved in the blood are also helpful to protect against microbes.

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Protection against bleeding is another important role of blood. Platelets and a cascade of plasma proteins known as clotting factors are important to form a blood clot and to stop bleeding when there is damage to a blood vessel by injury.

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