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An adult human has about 5 liters of blood running in the body.

The heart beats when we work hard or exercise and also when we are angry, excited or frightened of the body.

Blood is a liquid tissue. It has red blood cells, white bloods cells and plasma which are a fluid like water. Blood is transported around the body by the arteries and veins.

1. Carries oxygen and food to the cells
2. Removes carbon dioxide and waste materials
3. Transport hormones that control our body’s activities
4. Controls the temperature of the body by carrying away excess heat
5. Fights infection

The heart is a strong muscular organ. It is the size of one’s fist and is made up of cardiac muscles. The heart pumps blood continuously to keep it circling around the body. It beats about 72 times per minute. This is called the pulse. During this process, the walls of the blood vessels contract and expand. We can feel the pulse at various points in our body – at the wrist beneath the ears and at the base of the throat.

Oxygen – rich blood from the lungs is pumped out of the left side of the heart through the arteries. As the blood passes through the body, the oxygen and food are absorbed by the cells and carbon dioxide is released into the bloodstream. The blood becomes impure and bluish in color. Impure blood is carried back to the right side of the heart by the veins. From there the impure blood is taken to the lungs where oxygen is once again absorbed from the air sacs and the carbon dioxide is left behind. The lungs contract and push the carbon dioxide out. This process is repeated continuously.

The arteries and veins are connected by tiny blood vessels called capillaries. The absorption of food and exchange of oxygen and carbon dioxide takes place in the capillaries.