Double circulation in the Human heart

What is blood circulation?

One of the main functions of a circulatory system in animals is transporting oxygen throughout the body.

During blood circulation, blood is pumped to a gas exchange organ to obtain oxygen, then pumped to other parts of the body where it unloads the oxygen.

Before starting the lesson try to recall the structure of the human heart and the main vessels in our blood circulatory system.

The circulatory systems of different animals

There can be two types of circulatory systems seen in animals. They are

  1. Single circulatory system
  2. Double circulatory system

In a single circulatory system, blood is pumped from the heart to the gas exchange organ and then directly to the rest of the body.

In a double circulatory system, blood is first pumped from the heart to the gas exchange organ. Then back to the heart, and thereafter, to the rest of the body.

Differences between the single circulatory system and the double circulatory system

In relation to the transport efficiency of oxygen to other parts of the body, the double circulatory system is more efficient than the single circulatory system.

During double circulation, the heart pumps the blood twice. It is easier to maintain higher pressures within the blood vessels. Then blood travels more quickly to organs.

In the single circulatory system, like in fish, blood travels more slowly to the other organs due to the loss of pressure that occurs, when it passes through the gills.

These figures show the differences between these systems.

Double blood circulation

In humans, when the blood circulates once through the body it flows twice through the heart. This is called double circulation.

There are two parts in a double circulatory system:

  1. Pulmonary circulation
  2. Systemic circulation

The pulmonary circulation

Deoxygenated blood in the left ventricle is pumped, through the pulmonary arteries, and is circulated through the lungs, where it becomes oxygenated. The oxygenated blood flows back to the heart, via the pulmonary veins.

The systemic circulation

Oxygenated blood in the left ventricle is pumped, through the aorta, and is circulated through all other parts of the body, where it unloads its oxygen.

Deoxygenated blood from the upper and lower parts of the body, returns to the heart, through the vena cava.

So, in a summary, when the blood, circulates once through the body, it flows twice through the heart, via the double circulatory system.

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Anuradhika Lakmali

Anuradhika Lakmali is a co-founder of Science A Plus learning network. She is working as a government teacher and has interest in chemistry, biology, phisics and self development.