Q. 113.9( 135 Votes )

Describe double circulation in human beings. Why is it necessary?

Answer :

Blood circulation refers to the path taken by the blood throughout the body to transport the various gases and nutrients required. In human beings, the circulatory system is closed and double circulation takes place. In double circulation, the blood goes through the heart twice during each cardiac cycle. 
Mechanism of double circulation:
There are two pathways of blood flow in double circulation.


1. Systemic circulation
2. Pulmonary circulation


Systemic circulation:

  • The oxygenated blood is pumped into the aorta from where it circulates to the various parts of the body.
  • The deoxygenated blood is collected by veins and venules and pumped back into the superior vena cava and then to the right atrium.
  • When the deoxygenated blood enters, it gets carried to the right ventricle via the right atrium.
  • Here, it undergoes pulmonary circulation.


Pulmonary circulation:

  • The right ventricle pumps blood into the pulmonary artery.
  • TThis deoxygenated blood is carried to the lungs to get oxygenated. 
  • After oxygenation of the blood, it gets carried back and the pulmonary vein pumps this oxygenated blood to the left atrium which pumps it into the left ventricle.
  • The left ventricle pumps this oxygen-rich blood to the aorta for systemic circulation.



Double circulation is necessary in human beings in order to avoid mixing of oxygenated and deoxygenated blood which makes the circulatory system more efficient and helps in maintaining a constant body temperature (homeostasis).

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