When you travel by the train, have you ever looked at the tracks- how they run ahead leading you to your destination, sometimes going straight and sometimes crisscrossing, interconnecting with each other.

Similar is our circulatory system that consists of interconnecting blood vessels (tracks) through which the blood (train) travels carrying nutrients and oxygen to various parts of the body. Also, waste material is carried in the blood to be passed in the urine and the lungs..

The blood is pumped by the heart and thus keeps the circulation moving. Impure blood (also called venous circulation) enters the right side of the heart and passes to the lung through which oxygen enters the lungs and carbon dioxide is given out. This pure blood enters the left side of the heart (also called arterial circulation) and is distributed to the rest of the body to give oxygen and nutrients to all the cells of the body.