BLOOD AND ITS CONSTITUENTS
The blood is an opaque, rather viscid fluid, of bright red or scarlet colour when its flows from the arteries, of dark red or purple colour when it flows from veins. It is salty to the taste and has a peculiar faint odour. Its temperature is generally about 37°C. The circulatory system is filled with about 5 litre of blood in an adult.
Blood acts as a transport system of the body. It carries numerous cells and chemicals from one part of the body to another.
Its function includes:
Carrying oxygen and digested food.
Carrying carbon dioxide from the tissues.
Carrying waste products away from body cells.
Carrying cells which fights diseases and repair injury.
Clotting factor which prevents the loss of blood.
Carrying hormones.

Blood consists of several cell types floating in a fluid called plasma.

ERYTHROCYTES:
The red blood cells contains a pigment called haemoglobin which gives blood its red colour. Its main function is to carry O2 to the body and CO2 away from the body. They contain no nucleus. It can be describes as bi-concave non-nucleated discs. They are very small which allows them to pass through the capillaries. They can’t divide and replace themselves. But they are constantly produced in the body by the red marrow of certain bones. They have a life span of about 120 days.

LEUCOCYTES:
The white blood cells defend the body against disease. They do this by attacking the germs and repairing damage. They are made in several areas of the