The circulatory system is responsible for the transportation of nutrients, gases like oxygen, carbon dioxide, waste products etc. An important organ which initiates blood circulation is the heart. The whole blood circulating throughout the body passes through the heart and lungs for purification. Is heart the only organ that helps in purification? Let’s have a brief study on double circulation and organs involved.
Blood Circulation in Humans
In animals there are two types of circulatory systems: open circulatory system and closed circulatory system. Closed circulatory system is further classified into two based on number of times blood circulation takes place through heart i.e. single circulation (e.g. fish) and double circulation (e.g. humans).
In single circulatory system, the blood will pass through heart to gills then after purification, blood will be distributed to different parts of the body. Only one cardiac cycle is completed, hence the name single circulation.
Most of the mammals follow double circulation which provides efficient way of circulation. Heart is the key organ for blood circulation. In case of humans, heart is divided into four chambers left and right atria and left and right ventricles. Further, heart is connected to the lungs through pulmonary artery and vein.
Double circulation is the circulation of blood through heart twice while supplying the blood to the whole body. In double circulation, there are two loops or circuits where the blood travels to heart; They are:
• Systemic circulation: First stage of systemic circulation starts from left atrium to left ventricle. This transfers the oxygen rich blood to aorta for the supply to various parts of the body. Later, the veins and venules collect the blood from various parts of the body. This blood is rich in carbon dioxide than oxygen and is known as deoxygenated blood. Deoxygenated blood is poured into superior vena cava then to right atrium. Right atrium passes the blood to right ventricle for pulmonary circulation.
• Pulmonary circulation: The pulmonary artery collects the blood from right ventricle and passes to lungs for oxygenation. Lungs collects the deoxygenated blood supplied to it and purifies. Then the oxygenated blood is pumped back to left atrium of the heart through the pulmonary vein. Left atrium passes the blood to left ventricles where they pump the oxygenated blood to aorta for systemic circulation.
The double circulation maintains a strict separation of oxygenated and deoxygenated blood. Thus it ensures the high supply of oxygen and improves the body efficiency. Apart from the double circulation, a third portal system also exists to improve the circulation efficiency.
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