What are the four components of blood


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 - i.e. 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 in question 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.