Blood Circulation
Blood is the most important means of transportation in the body. In order to supply all parts or cells of the body with approximately 7000 liters (1820 gallons) per day the body needs its own efficient transportation system: the blood circulation with its several 1000 kilometer (621 Mile) long blood vessel system.
The circulatory function is performed with the aid of the heart which, acting as a pressure/suction pump, on the one hand forces the blood, into the large arteries of the general circulation and, on the other, sucks the blood from the large veins into the auricle.
Arteries are blood vessels that carry the blood away from the heart. To ensure the proper blood
supply to the organs, they branch out during their course.
Arteries have large walls consisting of elastic tissue. They receive the initial high pressure coming from the heart and transform it so that there is an even flowing stream in the smaller arteries and capillaries.
The nervous system controls the muscle cells in the artery walls.
When they contract, the diameter of the arteries becomes smaller and less blood flows through them.
This way, the blood supply to all areas is ensured in accordance with different situations, e.g. the storage of heat and the supply of heat when it is cold, increased blood supply for physical work, etc...
The arteries divide into arterioles and branch out further to become capillaries. These tiniest of blood vessels can be found throughout the tissues. Through them, osmosis with the cells takes place. Osmosis is performed through the very thin walls of the capillaries which are no obstacle for most substances.
After passing the capillaries, the blood stream increases again in size and passes on to the venules which first unite to form small veins and then unite again to form large veins. The large veins carry the blood back to the heart again.
One difference between the veins and the arteries is the thickness of their walls. The walls of the veins are thinner. The other difference is the blood pressure. It is considerably lower in the veins, although the volume of blood is considerably larger than in the arteries.
The color of the blood has changed in the meantime from light red (rich in oxygen) to dark blue-red (poor in oxygen, with added waste products and carbon dioxide), and the blood flow has become slower.
Due to the separation of the heart into a "right" and a "left heart", we distinguish two circulations, the lesser or pulmonary circulation and the larger or general circulation. The lesser and the general circulations are arranged one behind the other in the form of an 8.
