As animals grow in size and complexity, tissues and organs with specific functions developed each dependent onthe others for some essential process or chemicals. The need arose for a system to transport materials, especially food, oxygen, CO2 and wastes between the various organs. The circulatory system mediates the continuous movement of all body fluids.
The circulatory system helps in the following functions:
1. Transport of nutrients: Sugars, amino acids, minerals and vitamins are picked up by blood from intestine
and transported to different parts of the body for storage and assimilation.
2. Transport of oxygen: It transports oxygen from the respiratory surface to the tissues for utilization in
3. Transport of Carbon dioxide: CO2 formed during respiration is taken by blood to the respiratory surface
4. Transport of waste products: It carries nitrogenous wastes from various parts of the body to the kidneys for separation and elimination
5. Transport of hormones: Endocrine glands pour their hormones into blood for transport to target tissues.
6. Maintenance of water balance: Circulating blood provides water and inorganic salts in the region of
deficiency and removes the same in the area of excess.
7. Regulation of body temperature: Blood distributes heat to all parts of the body. It also conducts heat to the
surface for dissipation
8. Maintenance of pH: Blood maintains pH of tissue fluids with the help of various buffers.
9. Body defence: Blood contains phagocytic leucocytes, and immunocytes for defence against germs.