blood

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

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Blood is sometimes called "the red juice of life" because it is absolutely vital to the body. Among other things, it functions as a means of transport and communication and is essential for maintaining innumerable bodily functions. Read more about the tasks of blood, its composition, blood formation and health problems in connection with the red juice of life!

What is blood

Blood is a "liquid organ" that circulates in the body and reaches all organs and cells. The motor of this blood circulation is the heart. It pumps blood to the outermost periphery of the body and back again. Depending on the oxygen or carbon dioxide content, it is light red (arterial) to dark red (venous).

What is blood made of?

The blood is composed of the plasma (liquid component) and blood cells (corpuscular blood components).

The plasma consists primarily of water in which various substances are dissolved. These include nutrients, vitamins, electrolytes, hormones, gases, metabolic waste products (such as uric acid, creatinine) and, above all, various proteins (such as antibodies = immunoglobulins, fibrinogen, albumin, etc.). The plasma without the coagulant fibrinogen (factor I of blood coagulation) is called blood serum.

The blood cells swim in the blood plasma as solid components of the blood:

• red blood cells (erythrocytes): responsible for the transport of oxygen and carbon dioxide
• White blood cells (leukocytes): are the cellular components of the immune system and are divided into granulocytes, lymphocytes and monocytes
• Platelets (thrombocytes): important for blood clotting

All blood cells together make up around 47 percent of the blood in men and around 42 percent in women. This volume fraction of cells per unit of blood volume is known as the hematocrit.

Where is the blood made?

All blood cells have the same origin: the stem cells, which in the unborn child are in the liver and spleen, in adults in the red bone marrow of various bones (ribs, sternum, vertebral bodies, etc.). These stem cells are the only cells in the body that are pluripotent, which means that they can develop into almost all types of body cells and also make copies of themselves.

How many liters of blood does a person have?

The amount of blood in humans depends primarily on height and weight. For example, the blood volume in an adult is around seven percent of the lean body mass - around five to six liters. Men usually have a little more blood than women. The blood cells make up around 45 percent of the blood volume.

Blood types

If blood groups are mentioned, this usually refers to the so-called ABO system. This is the most important blood type system in humans. It is based on certain proteins on the surface of the red blood cells and distinguishes between four main groups: blood groups A, B, AB and 0 (some with subgroups and variants).

In Central Europe around 40 percent of people have blood group A and another 40 percent have blood group 0. The remaining 20 percent have blood group B or - rarely - blood group AB.

Rhesus factor

The rhesus system is another blood type system. It is also based on a certain surface protein of the erythrocytes (more precisely: on a group of related proteins). If the red blood cells have the Rhesus factor on their outside, the person concerned is Rh-positive (Rh-positive). If the rhesus factor is missing, one is rhesus negative (Rh negative).

The Rh system is particularly important during pregnancy, when a Rh-negative pregnant woman is expecting a Rh-positive child for the first time. At birth, some child blood can enter the mother's bloodstream. The woman's body then produces specific antibodies against the foreign substance rhesus factor. This can be dangerous if there is another pregnancy with a Rh-positive child later: Maternal antibodies against the Rh factor can get through the placenta into the unborn child's bloodstream and attack the child's Rh-positive erythrocytes. The child can develop dangerous anemia.

To prevent this, Rh-negative women who are expecting a Rh-positive child for the first time receive a drug that prevents the formation of Rh factor antibodies.

What is the function of blood?

One of the tasks of the blood is to supply all body cells with oxygen and nutrients. Other important substances such as hormones and antibodies are also distributed in the body via the bloodstream and carried to their destinations.

Another function of the blood is the removal of waste products in the direction of the excretory organs (kidneys, intestines, lungs, skin).

The liver is particularly well supplied with blood because it is the body's central metabolic organ. One of their tasks is the breakdown and conversion of nutrients that have been absorbed in the intestine and transported via the blood.

Since heat is also transported with the blood, the body can regulate the dissipation of heat and thus the body temperature by widening and narrowing the vessels.

The blood also helps to keep the acid-base balance in balance: Using buffer systems, it keeps its own acidity (blood pH value) as constant as possible at around 7.4.

The platelets (thrombocytes) and coagulation factors in the blood protect the body from major blood loss by forming a clot in the event of a vascular injury and thus sealing the leak.

Last but not least, the blood also plays an important role in the immune system: the various groups of white blood cells can fight foreign substances and pathogens that have entered.

Where is blood?

The entire blood in the body circulates in the closed blood circulation system, consisting of arteries, veins and the finest vessels (capillaries) as connecting pieces between the arterial and venous systems.

Which areas of the body are supplied with blood and how well is influenced by the current need. An example: At rest, most of the blood is found in the vessels of the digestive organs - the body has time to concentrate on absorbing nutrients. On the other hand, most of the blood flows into the skeletal muscles during vigorous physical exertion, because they need it very urgently. The blood flow to the digestive organs (and other parts of the body) is greatly reduced in this situation.

What problems can blood cause?

In anemia, either the number of erythrocytes is too low or the hemoglobin content of the erythrocytes is too low. In both cases, the oxygen transport is impaired. Anemia can have very different causes. It is often due to a disorder in blood formation, for example due to a lack of iron, vitamin B12 or folic acid. Excessive blood loss - acute or chronic - can also cause anemia.

Hemorrhagic diatheses are congenital or acquired coagulation disorders that are associated with an increased tendency to bleed. Examples are hemophilia ("blood disease"), myelodysplastic syndrome and Henoch-Schönlein purpura.

Another major blood disease is leukemia ("blood cancer"). The term actually describes various cancers of the blood-forming system, but they have one thing in common: the uncontrolled increase in abnormal white blood cells in the blood.

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