Blood Circulation

Biological system

Blood circulation system


Capillaries in the Lung

Pulmonary vein

Pulmonary artery

Left (right) atrium

Left (right) ventricle

Vena Cava


Capillaries in the body

Blood circulation system is a two-part system which includes pulmonary loop and systemic loop. Purpose of these two system is delivering nutrients and oxygen to all cells in the body. The blood circulation starts when the heart relax between two heartbeats. Blood flows from both two atria into ventricle and then expand. In the systemic circulation, the left ventricles pumps the oxygen-rich blood into the aorta. The blood flows from the aorta to the larger and smaller arteries into the capillaries network. Then the blood releases the oxygen and other nutrients, at the same time, it will absorb the carbon dioxide and waste substances. After this, the blood in the veins flows into the right atrium and right ventricle.

Now, the pulmonary circulation starts. The right ventricle pump the blood which carries little oxygen into the pulmonary artery which branched into two main parts: one going to the left lung, one to the right lung. When we breathe out, the carbon dioxide leaves our body. The fresh blood returns to the left ventricle of the heart through the pulmonary veins and left atrium.

Although the circulation system is made up of two cycles, they happen at the same time. The circulation system is step by step cycle. The elements control each other. They work together to help people to breathe in the oxygen and deliver the oxygen-rich blood into all cells of the body and breathe out the carbon dioxide to sustain people’s live. The volume of blood of an adult is about 8 percentage of his total weight. If the circulation system can not work normally, all the tissues will lose the ability of metabolism. At the same time, some important function of organ in the body will get damaged, especially to cerebral cortex.


Jessica Wang



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