Blood travels or circulates through the body through sort of pipes called blood vessels. The blood is pumped in to the blood vessel for circulation by heart.
The blood vessels are of three types called arteries, veins and capillaries. Arteries carry blood pumped by heart to other parts of the body. Veins return the blood to heart for pumping. Capillaries constitute a very large network of tiny blood vessels that reach every part of the body and connect arteries to veins.
The blood circulates in two separate network of blood vessels. The heart is like a two pump combined, so that blood in each of the two circulation network is pumped by heart separately. The first blood circulation network takes care of the general blood circulation of the body, circulating blood to each and every part of the body, carrying oxygen, food and other essential material required for functioning and growth of the body. It also collects carbon dioxide and other waste material generated in body. One special section of this part of the blood circulation is through the kidney which removes excess water and some other substances from the blood and expels them from the body in form of urine.The other network of blood circulation is devoted entirely to lungs for the purpose of respiration.
Left side of the heart which makes up stronger of the two pumps receives oxygen rich blood returned from lungs through the respiratory network. This blood is pumped by the heart and sent throughout the body. this blood supplies oxygen plus many other substances absorbed by blood from the digestive system or releases in blood stream by various organs for supplying wherever these are needed. In the course of its travel through it also picks up carbon dioxide and other waste material from the body. The excess water and waste material are also removed from the blood by urinary and sweating system during circulation. The blood with high carbon dioxide is returned to the right side of the heart. This completes one cycle of blood circulation through the first circulation network.
The blood circulation in respiratory network starts with blood with carbon dioxide being pumped by right side of heart to the lungs. In lungs the the carbon dioxide in the blood is removed and oxygen is relished. This oxygen rich blood, after circulation through the lungs is returned to the left side of heart. This completes one cycle of blood circulation through respiratory circulation network.