This consists of a network of blood vessels and the heart blood vessels. There are three types:
- Arteries- which carry blood away from the heart.
- Veins- which return blood to the heart.
- Capillaries- which link the arteries and veins.
Capillaries are tiny blood vessels with very thin walls consisting of only one layer of cells. They are the site of exchange of substances between the blood and body tissues,eg.nutrients,oxygen and cellular waste products. Blood vessels from a network that transports blood to:
- The lungs ( pulmonary circulation) where oxygen is absorbed from the air in the lungs and,at the same time,carbon dioxide is excreted from the blood into the air.
- Cells in all other parts of the body.
Heart. The heart is a muscular sac,which pumps blood round the body and maintains the blood pressure.
The heart muscle is not under conscious(voluntary) control. The rate is greatly increased during exercise,when body oxygen requirements are increased.
The rate at which the heart beats can be counted by taking the pulse. The pulse can be felt most easily where a superficial artery can be pressed gently against a bone. The wrist is the site most commonly used for this purpose.
