Functions of the blood


Every person has about 4-6 litres of blood flowing through his veins. This corresponds to about 8% of the body weight. The blood consists of different proportions, which all take on different tasks in the body.

For example, the components play an important role in the transport of nutrients and oxygen, but also for the immune system. A normal distribution of the individual components is therefore essential for the health of a person. If, for example, the blood cells are reduced or altered, anaemia can occur. The blood consists of a cellular part, about 45%, and an aqueous part (plasma). Due to the pronounced vascular system, the blood reaches all areas of the body where it can take over many transport and regulatory functions.


Through the blood, oxygen, nutrients, hormones and enzymes are transported to the body cells in the terminal organs and waste products such as urea and carbon dioxide are removed. The oxygen is transported from the heart to the organs via the arteries. The carbon dioxide produced there is transported through the veins from the organs back to the heart.

The carbon dioxide is breathed out through the small pulmonary circulation and oxygen is absorbed. Another function of the blood is the so-called homeostasis. This describes the regulation and maintenance of the water and electrolyte balance, as well as the body temperature and the PH value.

The blood distributes body heat through the vessels and thus keeps the body temperature constant. In addition, the blood has the function of closing wounds to prevent major blood loss. For this purpose, the blood platelets and coagulation factors form a blood clot. Finally, the blood also has a protective and defensive function. It serves to defend against pathogens, foreign organisms and antigens (special surface proteins on cells that can be specifically attacked by the immune system) by white blood cells, messenger substances and antibodies.

Tasks of the red blood cell

The task of the erythrocytes (red blood cells) is to transport oxygen to the organs. The oxygen is absorbed in the lungs and bound to the red blood pigment, haemoglobin, in the erythrocytes. Haemoglobin contains iron, which is essential for oxygen transport.

If the haemoglobin or iron is reduced or there are too few erythrocytes, they cannot transport enough oxygen and anaemia occurs. The affected people usually have very pale skin and often feel exhausted, tired and less capable. They also suffer from headaches and dizziness because the brain is no longer supplied with sufficient oxygen.

In order to get into all tissues and fit through the smallest capillaries, the erythrocytes must be very deformable. This is possible because they have no nucleus and are made of elastic fibres. If the erythrocytes are no longer sufficiently deformable, they no longer fit through the gaps between the individual cells that form a blood vessel and are therefore broken down.

However, they are normally also reproduced to the same extent. This new formation is stimulated by a hormone called erythropoietin (EPO), among other things. This is released in the kidney and then causes an increased production of erythrocytes in the bone marrow.

These erythrocytes are then fully functional again and are available to the circulation. When the erythrocytes arrive in the target tissue, the oxygen is released into the tissue and part of the carbon dioxide produced there is absorbed by the erythrocytes. The carbon dioxide is also transported bound to haemoglobin.

It returns to the heart and lungs through the veins, is released there and can be breathed out through the air. From there the cycle starts again. Another function of the red blood cells is to form a blood group.

This is defined by specific proteins (glycoproteins) on the surface of the erythrocytes. These proteins are also called blood group antigens. The most well-known groups of these antigens are the ABO system and the Rhesus system. The blood groups are important when a patient is given blood from another person because he or she does not produce enough of his or her own blood or has lost a lot of blood, for example, due to an injury (transfusions).