Body Fluids and Circulation

Double Circulation

Humans in the animal kingdom, show the highest levels of specialization. In fact, birds and mammals show a specialized feature called as the double circulation. If you have guessed that this has something to do with the circulatory system, you are bang on target.

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Double Circulation

A circulatory path is a path taken by the blood, wherein it travels throughout the different organs of the body through arteries and veins. In humans, it is a closed circulatory system that exists, as blood flows in closed blood vessels. The circulatory system is responsible for the transport of gases, nutrients, waste products etc.


(Source: Wikipedia)

Mechanism Of Double Circulation

Double circulation is the most efficient way of circulation. Here, in humans, the four-chambered heart, arteries, veins, and capillaries all have a vital role to play. Blood gets pumped out of the heart. This blood goes to different organs and then blood again comes back to the heart. All this happens in a very systematic way through the different arteries and veins carrying oxygenated and deoxygenated blood.

In double circulation, there are two pathways in which blood flows. They are:

  • Pulmonary pathway
  • Systemic pathway.

The pulmonary circulation or pathway carries the deoxygenated blood from the right side of the heart to the lungs.  Exchange of oxygen and carbon dioxide takes place in the lungs and the blood is now oxygenated (with oxygen).

Through the systemic circulation, oxygenated blood travels from the left side of the heart to the other areas of the body. At various organ sites, exchange of gases, nutrients, and waste through lymph occurs. This deoxygenated blood again goes back to the right side of the heart.

The pulmonary circuit and the systemic circuit work together. This ensures that deoxygenated blood goes to the lungs through the pulmonary artery while the oxygenated blood from the aorta reaches the different organs and tissues.

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Capillary exchange

Capillary Exchange

(Source: Wikipedia)

The arteries and veins have an extensive network throughout the body carrying oxygenated blood and deoxygenated blood.  The smallest of these arteries and veins are connected each other through the capillaries.

The capillaries at the arterial end allow materials such as water, glucose, oxygen, and amino acids to diffuse out. Capillaries also transport wastes and carbon dioxide to organs which can dispose of them. And so, the waste products enter near the venous ends of the capillaries. To maintain the blood volume, water diffuses in and out of capillaries.

Through the process of capillary exchange, oxygen leaves RBCs in the bloodstream and enters all the other cells of the body. Nutrients also diffuse out of the bloodstream into other cells. Simultaneously, the other cells expel the waste products which enter the capillaries. Carbon dioxide also diffuses out of the cells and enters into the capillaries, at the venous end.

These venous ends of the capillaries are connected with the smaller veins and venules, which join the larger veins. These veins now have deoxygenated blood. Through the main vein called as vena cava, blood enters the right atrium chamber of the heart, from where pulmonary circulation starts.

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Solved Questions For You

Q: What is the significance of double circulation in humans?

Ans: Double circulation is a distinguishing characteristic of the human circulatory system. It is very significant as it allows for proper circulation of blood, without the mixing of the oxygenated and deoxygenated blood. This separation of oxygenated and deoxygenated blood allows for an efficient supply of oxygen to the body cells and delivers a greater blood flow rate.

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