Blood cell formation

Vitamin B12 is essential to growth, cell reproduction, the manufacture of myelin (which surrounds some nerve fibers), and blood cell manufacture. The intrinsic factor, which is produced by cells in the stomach, is necessary for the absorption of vitamin B12 in the intestine A deficiency of the intrinsic factor results in abnormal formation of erythrocytes because of the body s failure to absorb vitamin B12, a necessary component for blood cell formation. The resulting anemia is a type of megaloblastic anemia called pernicious anemia. 

Granulocyte colony stimulating factor 127 amino acids E. coll Adjunct to cancer chemotherapy Approved for sale By stimulating white blood cell formation, aids recovery... 

About a quarter of the total body iron is stored in macrophages and hepatocytes as a reserve, which can be readily mobilized for red blood cell formation (erythropoiesis). This storage iron is mostly in the form of ferritin, like bacterioferritin a 24-subunit protein in the form of a spherical protein shell enclosing a cavity within which up to 4500 atoms of iron can be stored, essentially as the mineral ferrihydrite. Despite the water insolubility of ferrihydrite, it is kept in a solution within the protein shell, such that one can easily prepare mammalian ferritin solutions that contain 1 M ferric iron (i.e. 56 mg/ml). Mammalian ferritins, unlike most bacterial and plant ferritins, have the particularity that they are heteropolymers, made up of two subunit types, H and L. Whereas H-subunits have a ferroxidase activity, catalysing the oxidation of two Fe2+ atoms to Fe3+, L-subunits appear to be involved in the nucleation of the mineral iron core once this has formed an initial critical mass, further iron oxidation and deposition in the biomineral takes place on the surface of the ferrihydrite crystallite itself (see a further discussion in Chapter 19). 

The other hormone of note synthesized by kidney is erythropoietin (EPO), a glycosylated peptide hormone (molecular weight approximately 50 000), which promotes red blood cell formation and is secreted in response to poor oxygen perfusion (hypoxia) of the kidney. This, along with the control of blood pressure via the RAA system illustrates the importance of the kidney in regulating aspects of the blood vascular system. Further details of EPO can be found in Chapter 5. 

Mice given oral doses of 500 mg/kg/day for 5 weeks had testicular atrophy both red and white blood cell formation were also affected at this level. ... 

In 90-day inhalation studies (6 hours/day, 5 days/week) rats became hypersensitive to sound and touch and had mild hyperemia at 0.6ppm at 2.2ppm there was greater increase in splenic red blood cell formation, mild hemolytic anemia, and dermatitis. Severe testicular degeneration developed in the 2.2 ppm-exposed rats that did not return to normal during a 10-week postexposure observation period. Dogs similarly exposed at 0.6 and 2.2 ppm had some loss of appetite, diarrhea, lacrimation, and hind leg tremor. There was mild, reversible testicular degeneration in the males exposed at 2.2 ppm. 

Vitamins are small organic molecules which in small amounts are obligatory nutrients and used by the body as co-factors in a multitude of metabolic processes. They play a role in hormone production, are necessary for blood cell formation and for producing nervous-system constituents, and they are ingredients for the formation of genetic material. There are no chemical relationships between the various vitamins and mostly also their most physiological actions are not related. 

Hematopoietic development of blood cells begins mainly in the spleen and liver of the fetus during early pregnancy. By the seventh month, however, the marrow of a fetus becomes the primary site of blood cell formation [1]. During childhood, the marrow of the central axial skeleton such as the pelvis, spinal cord, and ribs, and of the extremities, such as the wrist and ankle, provides the key site of hematopoiesis. Hematopoiesis at the periphery (also known as extramedullary hematopoiesis) slowly decreases with age. Chronic administration of hematopoietic growth factors can reverse this decline. Severe hemolytic anemia and hematopoietic malignancies can also reverse the process. 

Another example is lead poisoning wherein acute toxicity symptoms are seen in the Gl tract. Chronic toxicity causes damage to blood cell formation and musculature and subtle decreases in mental ability. (See ASIDE 1) Frequent exposure to large doses can show both types of effects -this is called subacute. 

Copper is required for the activity of enzymes associated with iron metabolism, elastin and collagen formation, melanin production and the integrity of the central nervous system. It is required with iron for normal red blood cell formation. Copper is also required for bone formation, brain cell and spinal cord structure, the immune response and feather development and pigmentation. A deficiency of copper leads to poor iron mobilization, abnormal... 

Hypoxia can be the long-term result of reduction of blood cell formation in bone marrow. Some toxicants reduce the production of both erythrocytes and leukocytes in marrow, resulting in a... 

The urinary system removes excess water and nutrients and filters wastes from the circulatory system. Additionally, the urinaiy system aids in red blood cell formation and metabolizes vitamin D. The urinary system s organs include the kidneys, ureters, urinary bladder, and urethra. 

Hematopoiesis is the process of blood cell production that takes place in the bone marrow. Through a complex series of regulatory events, stem cells are differentiated into various types of cells, including red blood cells. Stem cell differentiation is responsive to exogenous stimuli and can be upregulated to resupply a deficient cell population. However, only a limited number of therapeutics (iron, hemin, or erythropoietin, for example) can stimulate Hb-replete red blood cell formation. Recognition of the poor bioavailability of many iron compounds or hemin compositions and the improved safety profile of a tHb relative to rmmodified Hb has renewed the interest in Hb administration as... 

Erythropoietin—A hormone made by the kidneys that is required for red blood cell formation in the bone marrow. Lack of this hormone leads to anemia. 

B. Excess folate, by overwhelming the folate pool trapped as N -methyltetrahydrofolate, can allow for formation of AI, A4°-methyl-enetetrahydrofolate which is required for the thymidylate synthase reaction for DNA synthesis and red blood cell formation. Folate is not recognized as a methyl donor by methionine synthase. Folate does not inhibit destruction of erythrocytes. Cobalamin is an important critical vitamin not synthesized by humans. 

There are also a large number of antibiotics structurally unrelated to penicillins and cephalosporins. These compounds exert their antimicrobial activity by inhibiting protein biosynthesis. In 1947 chloramphenicol (see Figure 3) was isolated from cultures of Streptomyces venezuelae. It is a broad-spectrum bacteriostatic agent that interferes with protein synthesis by binding to bacterial ribosomes. The use of chloramphenicol in humans is hmited because of the drug s toxicity. It inhibits liver enzymes and suppresses red blood cell formation. 

Each person produces approximately 10 red blood cells per day. Because so many cells must be produced, nutritional deficiencies in iron, vitamin B12, and folate prevent adequate red blood cell formation. The physical appearance of the cells in the case of a nutritional anemia frequently provides a clue as to the nature of the deficiency. 

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