Blood : definition, composition and functions | study science

                                                                        Blood

Blood is the fluid which flow in blood vessels. It is composed of plasma in which different types of cells are suspended. 

Blood is both a tissue and a fluid. It is a tissue because it is a collection of similar specialised cells that serve particular functions. These cells are suspended in a liquid plasma, which makes the blood a fluid.

Functions of blood

1. It transports oxygen from lungs to the cells.
2. It carries carbon dioxide, a waste product, from the body.
3. It carry cells and antibodies that fight infection.
4. Regulates pH, temperature, water content of cells.
5. It protect against blood loss through clotting.

Blood vessels

A tube through which blood circulates in the body is called blood vessels. There are 3 kinds of blood vessels: arteries, veins, and capillaries. 

                                                              

1. Arteries - it carry oxygen rich blood from heart to all parts of the body. Arteries have thick elastic walls as the blood flow is rapid and at high pressure.

2. Veins - it carry carbon dioxide rich blood from all parts of the body back to heart. Veins have thin walls. Valves are present in veins which allow blood to flow only towards the heart.

3. Capillaries - these are smallest blood vessels with thin wall. It connect arteries and veins. Oxygen and nutrients are exchanged for carbon dioxide and waste in capillaries.