Are blood cells made of atoms

The components of the blood

The "liquid" organ blood plays an important role not only in the transport of nutrients and waste materials, but also in the immune defense of the human body. The individual components of the blood and their meaning are briefly presented on this page.

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Blood cells
- erythrocytes (red blood cells)
- hemoglobin
Leukocytes (white blood cells)
- granulocytes
- monocytes
- lymphocytes
- thrombocytes (blood platelets)
Blood plasma
- albumin
- immunoglobulins
- coagulation factors
- lipoproteins
Functions of the blood
- mass transport
- Transport of gases
- Transport of solids
- Defense against pathogens
- Unspecific defense reaction
- Specific defense reaction
- wound closure
- heat distribution
Source references

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Introduction blood

An adult person has around 4.5 liters of blood, 55 percent by volume of liquid plasma, composed of water, albumin, immunoglobulins, coagulation factors and a number of other substances, and 45 percent by volume of blood cells, i.e. red and white blood cells and platelets.

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Blood cells

The blood cells form the solid components of the blood and are not formed in the blood itself, but in the bone marrow of the vertebral bodies, the sternum and the iliac crest, and in children also in the large limb bones.

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Erythrocytes (red blood cells)

The erythrocytes named after their most striking properties (Greek erythros = red and zytos = cell) give the blood the red color, which is caused by the hemoglobin contained in the erythrocytes. Erythrocytes are disk-shaped structures with a diameter of 7.5 µm and a thickness of 2 µm, which can be deformed significantly and thus forced through the narrowest capillaries (very thin blood vessels). External influences or diseases such as hereditary sickle cell anemia cause the erythrocytes to lose their ability to deform: this can block capillaries and damage tissue.

In a mm3 In blood there are an average of 5 million erythrocytes, i.e. the 5 liters of blood in an adult contain up to 25 trillion erythrocytes, or in other words: around half of all human cells (approx. 50 trillion) are erythrocytes. It may come as a surprise that half of all cells can be found in just 7% of the human body's volume, but erythrocytes, apart from sperm, are the smallest human cells.

Around 1 - 2 billion new erythrocytes are created in the bone marrow every day. While in children the bone marrow of the entire skeleton produces blood cells, in adults blood cell production is limited to the spine, pelvis, skull, sternum, hips and shoulders. The active bone marrow of an adult weighs a little more than 2 kg and is one of the largest organs.

Erythrocytes begin their existence as bone marrow cells called erythroblasts. - A "blast" is a non-specialized cell from which more specialized cells arise. - The erythroblasts have a cell nucleus and, like other cells in the body, can multiply. Some of the erythroblasts stop reproducing, fill with hemoglobin, lose their cell nucleus and finally enter the bloodstream as erythrocytes. These mature erythrocytes without cell nuclei survive in the blood for about 100 to 120 days. Then they are broken down in the spleen.

The task of the erythrocytes is the transport of oxygen from the lungs to the organs and tissues, which is made possible by the hemoglobin contained in the erythrocytes.

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Hemoglobin consists of proteins and four heme molecules, each of which can bind an oxygen atom by means of an iron atom. Hemoglobin accounts for around 70% of the 4 grams of iron that the human body contains. In addition to the oxygen (O2) the hemoglobin also transports the carbon dioxide (CO2) to the lungs, where it is exhaled.

Hemoglobin exists in three normal variants: Hemoglobin A contains two alpha and two beta chains and has a share of around 95% in adults. Hemoglobin A2 consists of two alpha and two delta chains and has a share of 2 - 4% in adults. Hemoglobin F is the most common type of hemoglobin in the fetus and has two alpha and two gamma chains.

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Leukocytes (white blood cells)

The blood cells, which are colorless in themselves, are called leukocytes (Greek leukos = white and zytos = cell) because they form a white paste when separated from the other blood cells. Leukocytes can be divided into three cell groups: granulocytes, monocytes (macrophages) and lymphocytes. While granulocytes and monocytes are formed exclusively in the bone marrow, lymphocytes are also formed in the spleen. The leukocytes form an important part of the human immune system.
The size of the leukocytes varies between 7-15 µm depending on the type. One mm3 Blood contains between 4,000 and 10,000 leukocytes.

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Granulocytes, which make up 65% of the white blood cells, contain characteristic cell nucleus granules, to which their name can be traced (Latin granula = granules). The granulocytes become active in the event of an infection or inflammation and have a lifespan of a few hours.


Around 10% of all white blood cells are monocytes. In contrast to granulocytes, the cell nucleus of monocytes consists of only one single part of the nucleus. Also known as macrophages, "giant phobia cells" eliminate pathogens and dead cells by eating and digesting them. Monocytes have a lifespan of 1 to 2 days.

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The lymphocytes, which make up 25% of white blood cells, are only temporarily present in the blood and circulate throughout the body or reside in the lymph nodes, the center of the immune system. The lymphocytes have two tasks: they form antibodies against intruders and they serve as a memory for the immune system to recognize pathogens. A single lymphocyte can produce up to 2000 antibody molecules per second. The memory cells under the lymphocytes survive for decades.

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Platelets (blood platelets)

The platelets are disc-shaped structures 1–3 µm in diameter that ensure that the blood stays within the veins. Small injuries to the vessels or cracks in the vessel wall are immediately stuck together with platelets. The platelets lose their disc shape, become spherical and have a prickly surface. An accumulation of platelets is called a thrombus. If such a blood clot becomes too large, it can clog a blood vessel. Per mm3 human blood contains between 150,000 and 400,000 platelets with a lifespan of 8 to 10 days.

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Blood plasma

The blood plasma, i.e. blood without blood cells, consists of 90% water. The remaining 10% are made up of proteins, salts and hormones. The most important plasma proteins are albumin, immunoglobulins, coagulation factors and lipoproteins. The task of the blood plasma is to transport blood cells, nutrients and waste products.

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Albumin is the most important blood protein in terms of quantity (60% of blood proteins). Albumin prevents the loss of water in the blood while it flows through the capillaries, which are permeable to water. It is also responsible for the transport of various blood components and nutrients.

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The immunoglobulins are formed by the lymphocytes and are actually antibodies which, together with the leukocytes, play an important role in the defense against pathogens.

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Clotting factors

The coagulation factors, fibrinogens, are responsible, together with the platelets, for blood clotting.

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The lipoproteins transport the fats and cholesterols ingested from food.

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Functions of the blood

The blood, which flows through the whole body in vessels, has four main tasks: to transport substances, to ward off pathogens, to close wounds and to distribute heat.

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Material transport

The body's cells get their energy by "burning" sugar with oxygen into carbon dioxide and water: C6H12O6 + 6 O2 => 6 CO2 + 6 H.2O. The blood is responsible for the transport of these substances.

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Transport of gases

The oxygen that reaches the lungs through inhalation is absorbed by the erythrocytes by means of hemoglobin and transported to the cells. In addition, the erythrocytes also absorb the waste product carbon dioxide created in the cells and transport it back to the lungs, where it can be exhaled.

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Transport of solids

The blood absorbs nutrients from the intestine and transports them to the cells. A distinction must be made between water-soluble and water-insoluble substances. Water-soluble substances such as B. Dextrose (C.6H12O6) are dissolved directly in the blood plasma, while substances that are insoluble in water, such as fats, are bound to proteins for transport. The waste solids produced by cells are carried by the blood to the liver or kidneys, where they are broken down or excreted.

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Defense against pathogens

In order to be able to defend itself against the numerous pathogens living in the environment, such as viruses, bacteria, fungi and animal parasites (e.g. malaria pathogens), the human organism needs a defense system. In the defense, which consists of the unspecific and the specific defense reaction, the leukocytes play an essential role.

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Nonspecific defense reaction

The unspecific defense reaction serves the first, rapid defense against pathogens. Alerted leukocytes, especially granulocytes, come to the pathogens. As a result, the affected part of the body becomes red and warm, swells and hurts: inflammation develops. The increase in body temperature causes a fever. The granulocytes try to destroy the pathogens by phagocytosis, "eating up". The granulocytes also die in the process. Later, the macrophages also reach the pathogens and help with phagocytosis. An accumulation of phagocytes creates pus.

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Specific defense reaction

The specific defense sets in slowly but more specifically than the unspecific defense. The lymphocytes play the main role. They recognize the pathogens entering the body and begin to form antibodies that match the pathogen exactly. The antibodies first combine with the intruders. The invaders are then "eaten up" (phagocytosed) by macrophages. After the pathogens have been destroyed, some lymphocytes retain the structure of the active antibody in their memory. If there is a renewed infection with a known pathogen, the corresponding antibodies can be formed very quickly. The pathogen is destroyed before it can spread. The body is immune to the disease, i.e. the disease no longer occurs or takes an easier course.

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Wound closure

Platelets and coagulation factors protect the body against blood loss in the event of minor injuries by stopping bleeding. Hemostasis consists of several steps: First, the injured blood vessels contract. Then the platelets attach to the edge of the vessel opening and close it within a few minutes. Finally, the coagulation factors are activated and an insoluble, thread-like protein, fibrin, is created in a multi-stage process, which holds the platelet plug together like a network and thus enables wound healing.

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Heat distribution

The human body has a constant temperature of approx. 37 ° C. The body temperature is created by the work of the cells. The blood transports the resulting heat through the body to all organs. Excess heat is led into the skin and radiated there to the environment. In a warm environment, the skin is also cooled by the evaporation of sweat.

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Source references

"The Blood: A Textbook for Biology Lessons", Rotkreuzstiftung, Central Laboratory Blood Donation Service SRK, Bern 1990.
Ed Uthman; "Understanding Anemia"; University Press of Mississippi;
"Hematology Primer";

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Questions, suggestions or corrections to [email protected] are welcome.

Matthias Giger, October 1999 (Update: January 31, 2002)