# 68 The circulatory system
The main transport system of human is the circulatory system, a system of tubes (blood vessels) with a pump (the heart) and valves to ensure one-way flow of blood.
Its functions:
- To transport nutrients and oxygen to the cells.
- To remove waste and carbon dioxide from the cells.
- To provide for efficient gas exchange.
The right side of the heart collects deoxygenated blood form the body and pumps it to the lungs.
The left side collects oxygenated blood from the lungs and pumps it to the body.
The double circulation
Beginning at the lungs, blood flows into the left-hand side of the heart, and then out to the rest of the body. It is brought back to the right-side of the heart, before going back to the lungs again.
This is call a double circulation system, because the blood travels through the heart twice on one complete journey around the body:
The left side collects oxygenated blood from the lungs and pumps it to the body.
The double circulation
Beginning at the lungs, blood flows into the left-hand side of the heart, and then out to the rest of the body. It is brought back to the right-side of the heart, before going back to the lungs again.
This is call a double circulation system, because the blood travels through the heart twice on one complete journey around the body:
- one circuit links the heart and lungs (low pressure circulation)
- the other circuit links the heart with the rest of the body (high pressure circulation).
The importance of a double circulation
- Oxygenated blood is kept separate from deoxygenated blood. The septum in the heart ensures this complete separation. Oxygenated blood flows through the left side of the heart while deoxygenated blood flows through the right.
- The blood pressure in the systemic circulation is kept higher than that in the pulmonary circulation. The left ventricle, with a thicker wall, pumps blood under higher pressure to the body and delivers oxygenated blood effectively to all parts of the body. The right ventricle has a thinner wall and pumps blood to the lungs under lower pressure, thereby avoiding any lung damage.
