Produce lymphocytes after birth

Blood and blood formation

Every adult person has around 5 to 6 liters of blood, which primarily takes on a transport function in the body: It supplies the cells with nutrients and oxygen, brings breakdown products such as carbon dioxide or urea to the relevant excretory organs and transports messenger substances that are formed by various glands , to the recipient tissues. In addition, the blood also contains elements of our body's defenses (immune system) and the components of blood clotting. In order to be able to take on these diverse tasks, blood consists of a whole range of different cells that are created from stem cells in the bone marrow in a process known as blood formation.

Normal blood formation (hematopoiesis)

The majority of the blood cells or blood cells are in the Bone marrow educated. The bone marrow itself is a spongy tissue found in the large bones of the body. In adulthood, blood formation takes place primarily in the bones of the spine, hips, shoulders, ribs, in the sternum and in the skull bones.
Since the blood cells only have a limited lifespan, new blood cells have to be formed constantly, several billion cells per day! In healthy people, blood formation is controlled in such a balanced way that only the number of cells that actually need to be replaced is formed. In the case of special requirements such as an infection, the body can also react in a targeted manner and increase the number of cells required, in this case the cells of the immune system.

The starting point of all blood cells are so-called Stem cells in the bone marrow. They divide and develop into progenitor cells for the two lines of blood cells: den myeloid Cells and the lymphatic Cells. Through further division and maturation (differentiation), the various types of mature blood cells, which are released from the bone marrow and can take over their function in the body, develop from these precursor cells via further intermediate stages.

Blood cells

About half of our blood is made up of blood plasma (water, proteins, other dissolved substances) and blood cells (blood cells). There are two series of blood cells: the so-called myeloid cells include red blood cells, blood platelets and the cells of the innate immune system, granulocytes and monocytes. B cells, T cells and natural killer cells, which are collectively known as lymphocytes and also belong to our immune system, make up the cells of the lymphatic series.

Red blood cells (erythrocytes)

The most important task of the erythrocytes is to transport oxygen from the lungs to the various organs and tissues and to bring carbon dioxide from the tissues to the lungs. The red blood pigment, hemoglobin, is required for the oxygen to bind to the blood cells. Red cells are the most numerous cells in the blood and, like most other blood cells, are made in the bone marrow. If there are too few red blood cells, it leads to paleness, tiredness, shortness of breath and other symptoms. The most important measurement for red blood cells is the level of hemoglobin in the blood. If the hemoglobin level is low, one speaks of anemia. In addition, the hemocrit value, which records the volume of erythrocytes in the total volume of blood, is also often determined during analyzes.

Blood platelets (thrombocytes)

The platelets are the smallest blood cells and got their name because of their shape. They are formed in the bone marrow and are responsible for blood clotting, known as hemostasis. Platelets ensure that, in the event of an injury, the walls of the blood vessels are sealed and platelet plugs form at the injured area within a very short time, which lead to hemostasis. The platelets later disintegrate and release substances that activate the clotting factors in the blood plasma. If there are not enough platelets, it can lead to spontaneous bleeding, e.g. small skin bleeding, or prolonged bleeding in the event of injuries, after dental treatment or increased menstrual bleeding in women.

White blood cells (leukocytes)

Granulocytes, monocytes and lymphocytes are collectively known as white blood cells or leukocytes and form the body's own immune system: Among other things, they detect pathogens such as bacteria and viruses and render them harmless. In most of the infectious processes associated with acute inflammation, their number is therefore significantly increased. In addition to their function in the defense against germs, they remove the waste materials that arise from the decay of body cells. The various leukocytes differ in terms of their appearance, their place of formation and their function, but can only ensure an optimal defense against infection through their interaction. If there is a lack of white blood cells, infections occur more frequently and the body is at risk from pathogens such as mold, which would not cause disease in healthy people. The total number of leukocytes is measured in the normal blood count. The respective number of granulocytes, lymphocytes and monocytes is determined in what is known as the differential blood count.


Granulocytes are found in the blood, bone marrow, and body organs. They are formed in the bone marrow and are the most important cells for defense against infection. A distinction is made between neutrophilic granulocytes, eosinophilic granulocytes and basophilic granulocytes on the basis of their different staining properties. The neutrophil level is measured as an important parameter for the function of the body's own defense against pathogens.


Monocytes are blood cells that migrate into the tissue and, as macrophages (so-called phagocytes), can absorb and eliminate infectious agents, dead cells, foreign bodies, etc. Monocytes are made in the bone marrow.


When it comes to lymphocytes, a distinction is made between B lymphocytes, T lymphocytes and so-called "killer cells". Lymphocytes are formed in the bone marrow and mature into functional defense cells in the other organs of the lymphatic system such as the lymph nodes, spleen and thymus gland. Lymph node accumulations can be found in the angle of the jaw, the armpit, in the groin area and in the abdomen. The spleen is an organ in the upper left abdomen below the costal arch, and the thymus is located behind the breastbone. Lymphocytes are also found in the lymph. It is a colorless, watery liquid in the lymphatic vessels, which, like the blood vessel system, forms an extensive network throughout the body. Lymphocytes are necessary for a functioning defense against infection, as they produce antibodies and in some cases can themselves destroy infectious agents and altered endogenous cells. They control the granulocytes and ensure that the body "remembers" infectious agents with which it has already been in contact.

The amount of the individual cell types in the blood is examined in what is known as the blood count.

Created by: Hehn (Information Center) on July 25, 2014, last change: March 31, 2015


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A blood test provides information about the amount and composition of blood cells.