Functions of the blood


Everyone has around 4-6 liters of blood flowing through their veins. This corresponds to about 8% of the body weight. The blood is made up of different parts, all of which perform 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.

Read more about the topic here: immune system

A normal distribution of the individual components is therefore essential for a person's health. If the blood cells are reduced or changed, for example, anemia (anemia) can occur. The blood consists of a cellular part, about 45%, and an aqueous part (plasma). Through the pronounced vascular system, the blood reaches all areas of the body and can take on many transport and regulatory functions there.


Oxygen, nutrients, hormones and enzymes are transported through the blood to the body cells in the end organs and waste materials such as urea and carbon dioxide are carried away. Of the oxygen gets through the arteries from the heart transported to the organs. The carbon dioxide produced there is returned to the organs via the veins to the heart transported. This is done through the small pulmonary circulation carbon dioxide exhaled and absorbed oxygen.

Another function of the blood is what is known as 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 the body heat through the vessels and thus keeps the body temperature constant.

In addition, the blood has the function of closing wounds in order to prevent major blood loss. For this, the platelets and coagulation factors form a blood clot.

Read more about the topic here Blood clotting

Finally, the blood also has a protective and defense function. It is used to defend against pathogens, foreign organisms and antigens (special surface proteins on cells that can be specifically attacked by the immune system) using white blood cells, messenger substances and antibodies.

Tasks of the red blood cells

The job of erythrocytes (red blood cells) is to Carrying oxygen to the organs. The oxygen is absorbed in the lungs and in the erythrocytes to the red blood pigment, the hemoglobin, bound. That contains hemoglobin iron, which is essential for the transport of oxygen. If the hemoglobin or iron are decreased or there are too few erythrocytes, they cannot carry enough oxygen and it comes to anemia. The people affected usually have one very pale skin and often feel exhausted, tired and less powerful. They also suffer from a headache and dizzinessbecause the brain is no longer adequately supplied with oxygen.

Read more about the topics here hemoglobin and Anemia

In order to get into all tissues and fit through the smallest capillaries, the erythrocytes have to very malleable be. This is possible because they no core and are made of elastic fibers. 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 usually reproduced to the same extent. This new formation is caused, among other things, by a hormone called Erythropoietin (EPO) stimulates. This is in the kidney released and then takes care of the Bone marrow for an increased formation of erythrocytes. These erythrocytes are then fully functional again. When the erythrocytes arrive in the target tissue, the oxygen is released into the tissue and part of the carbon dioxide created there is absorbed into the erythrocytes.

Read more about the topic here Erythrocytes

The carbon dioxide is also transported bound to hemoglobin. It reaches the heart and lungs via the veins, is released there and can be exhaled through the air. From there the cycle starts all over again. Another function of the red blood cells is the formation of a blood type. This is defined by specific proteins (glycoproteins) on the surface of the erythrocytes. These proteins are also called blood group antigens. Probably the most well-known groups of these antigens form this ABO system and the Rhesus system. Blood groups are important when it comes to giving someone else's blood to a patient because they are not producing enough themselves or have lost a lot of blood, for example due to an injury (transfusions).

Read more about the topics here blood type and Transfusion

Tasks of the white blood cells

The white blood cells (leukocytes) serve the immune defense. They are important in the defense against pathogens and also in the development of allergies and autoimmune diseases. There are many subgroups of leukocytes. The first subgroup is the neutrophil granulocytes with about 60%. They can recognize pathogens, absorb them and kill and digest them using specific substances. But the granulocytes also perish.

The next group is the eosinophil granulocytes with about 3%. They are particularly involved in parasitic diseases (e.g. worms) and allergic reactions of the skin, mucous membranes, lungs and gastrointestinal tract. They also contain substances that are toxic to cells and can thus ward off pathogens. They also activate additional immune cells.

The third group are the basophilic granulocytes (approx. 1%). The function of these granulocytes is still relatively unclear. So far, we only know that they have a receptor for a certain antibody (IgE) that is associated with the development of allergic reactions. Next come the monocytes (6%). They migrate into the tissue and develop into so-called macrophages (scavenger cells). These can also absorb and digest pathogens (phagocytosis) and thus fight various infections. In addition, they can present the fragments of the degraded pathogens on their surface (antigens) and thus enable the lymphocytes (last group) to give a specific immune response with antibodies.

The last group are the lymphocytes (30%). They can be further subdivided into natural killer cells and T and B lymphocytes. The natural killer cells recognize the infected cells (pathogens) and kill them. Together, the T and B lymphocytes are able to specifically attack the pathogen. On the one hand, this happens through the formation of antibodies, which then interact with the antigen of a pathogen, making it more vulnerable to the immune system. On the other hand, they also develop memory cells so that the immune system can immediately recognize and break down a pathogen on second contact. Finally, these cells also release substances that kill infected body cells. Only through the interaction of all these cells and specific messenger substances can the immune system work properly and protect the body from pathogens.

Read more about blood counts and white blood cells here

Functions of the platelets

The platelets (blood platelets) are responsible for that Blood clotting and hemostasis (Hemostasis). In the event of an injury to the vessel, the platelets quickly reach the appropriate location and bind to specific receptors in the exposed structures (e.g. Collagen). This is how they are activated. This process is also called primary hemostasis. After activation, the platelets release various ingredients that attract more platelets. The activated platelets form one Plug (red thrombus).

In addition, the coagulation cascade in the blood plasma activated, which leads to the formation of fibrin threads and an insoluble fibrin network. One speaks here of the white thrombus. In this way, the injuries to the vessel walls are closed very quickly and the bleeding is stopped. If the platelet count is too low, nose or gum bleeding or minor skin bleeding may occur. Even with minor injuries, bruises or bleeding into internal organs are possible.

Read more about blood clotting and here Platelets

Functions of the electrolytes

Various electrolytes are dissolved in the blood. One of them is sodium. Sodium is much more concentrated in the extracellular space, which also includes the blood plasma, than within the body's cells. It is this difference in concentration that enables special signal transmissions in the cell. Sodium is also important in distributing the water as it draws water with it.

Read more about the topic here sodium

Another important electrolyte is potassium. This is much more concentrated inside the cell than outside and is used to convey information, stimulate muscles and regulate intracellular fluid.

Read more about the topic here potassium

The next important electrolyte is calcium. Calcium comes in especially Teeth and bones and is generally much more concentrated outside the cells (including in the blood) than in the cells. Calcium is also important for that Muscle excitation, but also for blood clotting and the regulation of hormones and enzymes.

Read more about the topic here calcium

Also magnesium is an important electrolyte for the function of muscles and enzymes. The next fabric is phosphate. It serves as a buffer system, i.e. it ensures that the pH value remains largely constant by balancing acids and bases. It also occurs in the bone. The last important electrolyte is that chloride. It is important to keep the difference in concentration between the cell and the space outside the cell constant.

Read more about the topics here Magnesium, Blood chloride and electrolytes

PH value

The pH of the blood is usually between 7.35 and 7.45. It is determined by the amount of hydrogen ions and depends on the ratio of acids and bases to one another. In the blood these are mainly carbon dioxide (CO2) and bicarbonate (HCO3-). The blood pH is kept as constant as possible using various buffers. The most important one is bicarbonate. The pH value can also be regulated through increased exhalation of CO2 or the excretion of hydrogen ions in the urine. It is very important to keep the blood pH value constant, otherwise life-threatening imbalances in the acid-base balance can occur, such as acidosis (over-acidification) or alkalosis (too many bases).

You can find more information on this topic at: pH in the blood

Composition of the blood

The blood consists of a cellular part, the blood cells, and a liquid part, the blood plasma. The cells make up about 45% and can be divided into erythrocytes, platelets and leukocytes. The erythrocytes make up about 99% of the cells. The blood plasma is a yellowish liquid. It consists of 90% water, 7-8% proteins and 2-3% low molecular weight substances. Blood plasma without fibrinogen is called blood serum.

The following topic could also be of interest to you: Blood gas analysis

Functions of the blood plasma

The blood plasma is especially important for the transport of various substances. It not only transports blood cells, but also metabolites, nutrients, hormones, coagulation factors, antibodies and breakdown products of the body. Besides, it's for the Distribution of heat important in the body and contains the buffers that keep the pH constant. The main part of the proteins in the blood plasma is albumin with approx. 60%. Among other things, albumin is an important transport protein for substances that are not soluble in water. The other proteins are the so-called Globulins (approx. 40%). They are made up of complement factors (parts of the immune system), enzymes, enzyme inhibitors (enzyme inhibitors) and antibodies and are increasingly present, for example, in inflammatory or immune reactions.

Blood formation

Blood formation, also known as hematopoiesis, is the formation of blood cells from blood cell-forming stem cells. This is necessary because the blood cells are only one limited life to have. Erythrocytes live up to 120 days and platelets up to 10 days, after which they must be replaced. The 1st place of blood formation is in Yolk sac of the embryo. Here are the first up to the 3rd embryonic month Erythrocytes (still with core) formed, as well as Megakaryocytes (Precursor of platelets), Macrophages (Phagocytes) and hematopoietic stem cells (blood-forming stem cells from which all blood cells arise).

From the 2nd embryonic month also produces blood cells in the liver. These are the first mature erythrocytes. The fetal liver is also responsible for the maturation and multiplication of stem cells that later migrate to the bone marrow. The hematopoietic stem cells are in the embryo in the placenta, the AGM region (aorta, genital organs, kidney region) and in the yolk sac.

From the 4th fetal month, blood formation takes place in spleen and Thymus instead of and from the 6th fetal month in the spleen and Bone marrow. After the birth, the so-called adult blood formation begins. This takes place mainly in the bone marrow. There are different cell lines involved in blood formation. One is that Myelopoiesis. The erythrocytes, thrombocytes, granulocytes and macrophages emerge from it. The second cell line is the Lymphopoiesis. The various lymphocytes arise from it.

Read more about the topic here Bone marrow