Blood is the liquid substance or tissue found in the body.  About 55% of blood is plasma. And 90% of the plasma is water, while the remaining components is nutrients and other cells.

Composition of blood

The blood composed of four basic components, namely:

• Red blood cells
• White blood cells
• Platelets
• Plasma

RED BLOOD CELLS
The red blood cell are spherical in shape and appear red in color. The red color nature of the red blood cells is due to the fact that it contains haemoglobin. The presence of haemoglobin in red blood cells enable them to carry and transport oxygen from the lungs to other parts of the body’	They are concave or spherical in shape. They lack nucleus. They live for 120 days only

WHITE BLOOD CELLS
White blood cells are responsible for the protection of man from diseases. They form special cells called lymphocytes	They are concave or spherical in shape They have nucleus.

PLATELETS
Platelets are not true cells. They are microscopic fragments of other cells. They are formed in the bone marrow and have a life span of 7-11 days.  They help in blood clotting

d. BLOOD PLASMA

The blood plasma is the fluid components of the blood. It is yellowish and consists of water, proteins (albumen, gamma globulin and clotting factors) vitamins, minerals, salts, nutrients and other waste metabolic products.

• Albumin is the main protein in blood. It helps regulate the water content of tissues and blood.
• Gamma globulin is composed of tens of thousands of unique antibody molecules.
• Clotting factors, such as fibrinogen, are involved in forming blood clots that seal leaks after an injury. Plasma that has had the clotting factors removed is called serum.

Functions of blood:

Some of the major functions of the blood are as follows:

• Transportation of product of digestion, water, waste products, oxygen, carbon dioxide, hormones etc
• Homeostasis- Regulation of the body temperature,
• PH regulation- regulate body PH
• Coagulation
• Body protection