Histology of the circulatory system
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Red blood cell
From Wikipedia, the free encyclopedia
Human red blood cells
Red blood cells are the most common type of blood cell and the vertebrate body's principal means of delivering oxygen from the lungs to body tissues via the blood.
Whitney cells are also known as RBCs or erythrocytes (from Greek erythros for "red" and kytos for "hollow", with cyte nowadays translated as "cell"). A schistocyte is a red blood cell undergoing fragmentation, or a fragmented part of a red blood cell.
Human erythrocytes
Erythrocytes: (a) seen from surface; (b) in profile, forming rouleaux; (c) rendered spherical by water; (d) rendered crenate by salt. (c) and (d) do not normally occur in the body.
The diameter of a typical human erythrocyte disk is 6–8 µm, much smaller than most other human cells. A typical erythrocyte contains about 270 million hemoglobin molecules, with each carrying four heme groups.
Adult humans have roughly 2–3 × 1013 red blood cells at any given time (women have about 4 million to 5 million erythrocytes per cubic millimeter (microliter) of blood and men about 5 million to 6 million; people living at high altitudes with low oxygen tension will have more). Red blood cells are thus much more common than the other blood particles: There are about 4,000–11,000 white blood cells and about 150,000–400,000 platelets in a cubic millimeter of human blood. The red blood cells store collectively about 3.5 grams of iron, more than five times the iron stored by all the other tissues combined.
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, at a rate of about 2 million per second. (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. Just before and after leaving the bone marrow, they are known as reticulocytes which comprise about 1% of circulating red blood cells. Erythrocytes develop from stem cells through reticuloctyes to mature erythrocytes 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 heme constituent of hemoglobin is eventually excreted as bilirubin.
The blood types of humans are due to variations in surface glycoproteins of erythrocytes.
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, frozen and stored, to be reinjected shortly before the competition. (Red blood cells can be conserved for 5 weeks at −78 °C.) This practice is hard to detect but may endanger the human cardiovascular system which is not equipped to deal with blood of the resulting higher viscosity.
White blood cell
From Wikipedia, the free encyclopedia
White blood cells or leukocytes are cells which form a component of the blood. They are produced in the bone marrow and help to defend the body against infectious disease and foreign materials as part of the immune system.
A scanning electron microscope (SEM) image of normal circulating human blood. One can see red blood cells, several knobby white blood cells including lymphocytes, a monocyte, a neutrophil, and many small disc-shaped platelets.
There are normally between 4x109 and 11x109 white blood cells in a litre of healthy adult blood — about 7,000 to 25,000 white blood cells per drop. In conditions such as leukaemia this may rise to as many as 50,000 white blood cells in a single drop of blood. As well as in the blood, white cells are also found in large numbers in the lymphatic system, the spleen, and in other body tissues.
Nomenclature
The name "white cells" derives from the fact that after centrifugation of a blood sample, the white cells are found in the Buffy coat, a thin layer of nucleated cells between the sedimented red blood cells and the blood plasma, which is white in color (or sometimes green, if there are large amounts of neutrophils in the sample, which are high in green myeloperoxidase).A drop of blood can contain anywhere from 7000 to 25000 white blood cells
Types
There are many different types of white blood cells. One primary technique to classify them is to look for the presence of granules, which produces the categories "granulocytes" and "agranulocytes".
Granulocytes: As Granular Leukocytes and polymorphonuclear leucocytes (informally, "PMNS" or "Polys"), Granulocytes are a category of white blood cells, characterised by the fact that all types have differently staining granules in their cytoplasm on light microscopy. These granules are related to lysosomes found in some regular cells and primarily act in the digestion of engulfed invaders. There are three types of granulocytes: neutrophils, basophils, and eosinophils (named according to their staining properties).
Agranulocytes: Agranulocytes are a category of white blood cells which are characterized by the absence of granules in their cytoplasm. There are two types of agranulocytes: lymphocytes and monocytes.
These categories can be further broken down as follows:
| Type | Image | Diagram | Approx. % in humans | Description |
| Neutrophil |  |  | 65% | Neutrophils deal with defense against bacterial infection and other very small inflammatory processes and are usually first responders to bacterial infection; their activity and death in large numbers forms pus. |
| Eosinophil |  |  | 4% | Eosinophils primarily deal with parasitic infections and an increase in them may indicate such. |
| Basophil |  | | <1% | Basophils are chiefly responsible for allergic and antigen response by releasing the chemical histamine causing inflammation. |
| Lymphocyte | | | 25% | Lymphocytes are much more common in the lymphatic system. The blood has three types of lymphocytes:
B cells: B cells make antibodies that bind |
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