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5.1. General organization of the circulatory system

General organization of the circulatory system

The nutrients obtained by the digestive system and the oxygen from the respiratory system have to reach the cells so that they can carry out cellular respiration. In the same way, the products and waste substances of metabolism must be transported to other parts of the body or expelled to the outside by the excretory system. The one in charge of carrying out this transport is the circulatory system, consisting of a system of tubes, the blood vessels, which reach all the cells of the body, through which the blood circulates, which is driven by the heart.

The cells obtain the nutrients and the oxygen that the circulatory system takes from the internal environment, the environment in which they live immersed and to which they also discharge the excretory substances resulting from metabolism.

The internal environment is made up of interstitial plasma, a liquid that occupies the spaces between cells. Interstitial plasma is formed from the blood, and has to be continually renewed so that nutrients are not depleted or excretion products accumulate. The interstitial plasma, in addition to nutritional functions, has defensive functions.

But the best known fluid in the body is blood, which circulates inside the blood vessels and is responsible for transporting substances that will leave the blood vessels and renew the interstitial plasma.

The excess interstitial plasma is collected by a drainage system and forms another fluid, lymph.

Therefore, the circulatory system is made up of:

  • The blood circulatory system, made up of the heart  and blood vessels, which carry blood throughout the body.
  • The lymphatic system, made up of lymphatic capillaries, lymphatic veins , and lymph nodes through which lymph circulates.

Sangre y plasma


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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.