The circulatory system in humans is a network of blood vessels through which the heart pumps the blood and keeps the blood in circulation. The circulation system provides blood to each cell in the body.

The circulatory system comprises of two sub systems – cardiovascular system and the lymphatic system. The cardiovascular system consists of the heart, blood and the blood vessels in the form of arteries and veins. The lymphatic system consists of the lymph vessels, lymphatic nodes and lymph.

There are two categories of blood vessels – arteries and veins. The arteries carry the oxygenated blood from the heart to the rest of the body where it distributes the oxygen and nutrients. The veins carry the deoxygenated blood from the body organs back to the heart. The heart pushes the deoxygenated blood to the lungs, where the blood exchanges the carbon dioxide with fresh oxygen and is returned to the heart for recirculation to the body organs. When the blood reaches the intestines, it collects nutrients for distribution and discards the waste collected from the body cells to the intestines. The blood carries the oxygen and the nutrients to the tissues of the body where it exchanges them with carbon dioxide and waste from the cells. Waste like toxins are released into the kidneys.

Another important role of blood is to carry the white blood platelets that have the capacity to fight germs and contain diseases to the infection areas. Therefore, blood helps the immune system of the body.

The circulation system therefore aids some of the other organ systems like the respiration system, the digestive system, the immune system and the excretory system.

Therefore, as you must have noticed, the main parts of the circulation system are:

Heart
Blood Vessels
Blood
Lymph