Red blood cell
The other cells in the blood, the white blood cells, are actually immune cells.
Erythrocytes deliver oxygen via hemoglobin, a complex molecule containing heme groups whose iron molecules temporarily link to oxygen molecules in the lungs or gills and release them throughout the body. Hemoglobin also carries some of the waste product carbon dioxide back from the tissues. (Less than 2% of the total oxygen, and most of the carbon dioxide are also held in solution in the blood plasma). Red blood cells consist of almost 90% hemoglobin; the heme is what gives blood its red color. A related compound, myoglobin, acts to store oxygen in muscle cells.
Mammalian erythrocytes
Erythrocytes in mammals are anucleate when mature, meaning that they lose their cell nucleus and thus their DNA. (Amphibian and bird erythrocytes have nuclei.) Erythrocytes also lose their mitochondria and produce energy from glucose, via glycolysis followed by lactic acid fermentation.
Human erythrocytes
Human erythrocytes have a flattened ovate shape, depressed in the center. This shape is optimized for the exchange of oxygen with the surroundings. The cells are flexible so as to fit through tiny capillaries, where they release their oxygen load.
The diameter of a typical erythrocyte is 6-8 µm. The blood types of humans are due to variations in surface glycoproteins of erythrocytes.
Adult humans have roughly 2-3 × 1013; red blood cells at any given time (women have about 4-5 million erythrocytes per cubic millimeter of blood and men about 5-6 million). Red blood cells are thus much more common than the other blood particles: about 4-11 thousand white blood cells per cubic millimeter, and about 150-400 thousand platelets per cubic millimeter.
The process by which red blood cells are produced is called erythropoiesis. Erythrocytes are continuously being produced in the red bone marrow of large bones. (In the embryo, the liver is the main site of red blood cell production.) The production can be stimulated by the hormone erythropoietin (EPO), which is used for doping in sports. Erythrocytes develop in about 7 days and live a total of about 120 days. The aging cells swell up to a sphere-like shape and are engulfed by phagocytes, destroyed and their materials are released into the blood. The main sites of destruction are the liver and the spleen. The hemoglobin is eventually excreted as bilirubin.
The spleen also acts as a reservoir of red blood cells, but this effect is somewhat limited in humans. In some other mammals such as dogs and horses, the spleen sequesters large numbers of red blood cells that are dumped into the blood during times of exertion stress, yielding a higher oxygen transport capacity.
Red blood cells can be separated from blood plasma by centrifugation. During plasma donation, the red blood cells are pumped back into the body right away, and the plasma is collected. Some athletes have tried to improve their performance by doping their blood: first about 1 liter of their blood is extracted, then the red blood cells are isolated and frozen, and they are reinjected shortly before the competition. (Red blood cells can be conserved for 5 weeks at -78° Celsius.) This practice is hard to detect but may endanger the human cardiovascular system because it is not equipped to deal with blood of the resulting higher viscosity.
Diseases involving the red blood cells include:
- An anemia (or anaemia) is a disease characterized by low oxygen transport capacity of the blood, because of low red cell count or some abnormality of the red blood cells or the hemoglobin.
- Iron-deficieny anemia
- Pernicious anemia
- Sickle-cell anemia is a genetic disease which leads to mis-shaped red blood cells.
- Thalassemia is a genetic disease that results in the production of abnormal hemoglobin molecules.
- The malaria parasite spends part of its life-cycle in red blood cells and feeds on hemoglobin. Both sickle-cell anemia and thalassemia are more common in malaria areas, because these mutations convey some protection against the parasite.
- A surplus of red blood cells occurs in a disease called polycythemia vera.
| Health science - Medicine - Hematology |
| Hematological malignancy and White blood cells |
| Lymphoma (Hodgkin's disease;, NHL) - Leukemia (ALL, AML, CLL, CML) - Multiple myeloma; - MDS - Myelofibrosis - Myeloproliferative disease; (Thrombocytosis, Polycythemia) - Neutropenia |
| Red blood cells |
| Anemia - Hemochromatosis - Sickle-cell anemia; - Thalassemia - other hemoglobinopathies |
| Coagulation and Platelets |
| Thrombosis - Deep venous thrombosis; - Pulmonary embolism; - Hemophilia - ITP - TTP |
| Cardiovascular system - Blood | Edit |
| Red blood cells - White blood cells - Platelets - Blood plasma | |
| White blood cells | |
| Granulocytes (Neutrophil granulocytes;, Eosinophil granulocytes;, Basophil granulocytes;) - Lymphocytes - Monocytes | |
| Coagulation | |
| To be filled - FVIII- vWF |