Transport of breathing gases in the blood

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The gas exchange between blood and breath takes place in the alveoli, the alveoli. But how are the breathing gases oxygen and carbon dioxide actually transported from the alveoli to the cells and back? The erythrocytes in the blood, more precisely the hemoglobin, are of essential importance.

The breathing gases are mainly transported via the hemoglobin of the red blood cells.
The breathing gases are mainly transported via the hemoglobin of the red blood cells.

This gas exchange takes place between blood, air and cells

  • It is well known that when we breathe, oxygen is absorbed and carbon dioxide is given off. The blood acts as the transport medium (see below). There are two places where gas is exchanged: once in the alveoli (air sacs) between blood and breath and once between blood and body cells.
  • In the alveoli, the blood absorbs oxygen and releases carbon dioxide. This is called external breathing. The blood enriched in this way then undertakes a second gas exchange with the cells of the organism: oxygen is given off here and carbon dioxide is absorbed as a metabolic product. But how exactly are these breathing gases actually transported?

This is how the breathing gases are transported in the body

  • In vertebrates (including humans, of course), oxygen is transported via hemoglobin, the red blood pigment found in erythrocytes. Hemoglobin is a protein molecule to which four iron-containing heme are bound. The oxygen binds to the iron in the heme. This is how oxyhemoglobin is created. In the capillaries, the oxygen is first released again by the hemoglobin and passed on to the tissue. A small part of the oxygen is also transported as oxygen molecules dissolved in the plasma.
  • Carbon dioxide is also one of the breathing gases. It is a metabolic product and has to be released from the body through the exhaled air. Carbon dioxide is transported as carbonic acid. The hydrogen ions are mostly bound to hemoglobin, while the bicarbonate is HCO3 is transported in the plasma. Of course, in order to breathe out the carbon dioxide, these reactions have to be reversed.

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