Functions of blood

The functions of blood can be grouped into three main categories: TransportDefence and Reproduction.
1. Transport
a. Oxygen combines with haemoglobin in the red blood cells to form oxyhaemoglobin in the lungs. The oxygen is carried in this form in the blood from the lungs to the tissues.

b. Some Carbon (lV) oxide combines with haemoglobin and is transported to the lungs to be excreted. Most Carbon (1V) oxide however. is transported in the plasma as hydrogen carbonate.

c. Digested soluble food substances, such as glucose, amino acids and lipids are carried by blood from the small intestines to all cells of the body.

d. Metabolic waste substances. such as urea, are transported by the blood to excretory organs like kidneys and skin to be excreted from the body.

e. Hormones, such as insulin, secreted by endocrine glands are transported by the blood to their target organs.

f. Blood transports heat produced in parts of the body, such as the liver, to all parts of the body. This helps to maintain the body temperature of mammals constant
which makes them warm-blooded or Homoithermic.

2. Defence 

a) Leucocytes help to defend the body against pathogenic microbes, as well as toxins that these microbes may produce. They also help to remove unwanted materials, and worn-out tissues from the blood.

b) The blood platelets help in blood clot formation, which protects the body against excessive bleeding and entry of pathogenic microbes through cuts in the skin. It also helps wounds to heal faster.

3. Reproduction

 a) Blood is essential in mammals to make the penis erect, to enable sexual intercourse or copulation to successfully take place. This enables the male mammal to introduce sperms into the female.