Blood cell production, process

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... 

Over the last thirty years or so, our understanding of the complex mechanisms and interactions which regulate blood cell production has increased greatly. It is now recognized from experimental studies that cells are produced and mature within the bone marrow space from the relatively small population of pluripotent stem cells which comprise approximately 0.01-0.05% of the total nucleated marrow cell population and are established during embryogenesis (Metcalf and Moore, 1971). The two characteristic features of stem cells are that they have enormous ability to proliferate to produce more stem cells, a process known as self-renewal, and that they... 

The finite life span of most mature blood cells requires their continuous replacement, a process termed hematopoiesis. New cell production must respond to basal needs and states of increased demand. Red blood cell production can increase >20-fold in response to anemia or hypoxemia, white blood cell production increases dramatically in response to a systemic infection, and platelet production can increase 10-20-fold when platelet consumption results in thrombocytopenia. 

Hematopoiesis is the continual process of blood cell production and tbe development of the various cell lines. Blood cells are the progeny of a hemato-poetic stem cell. Through the process of hematopoiesis, the body is supplied with ample blood cells of aU lines. The hematopoetic stem cell can both replicate itself and differentiate into the mature cells found normally in the peripheral blood. The hematopoietic system includes the bone marrow, liver, spleen, lymph nodes, and thymus. Regulatory growth factors also play a role in hematopoiesis. 

Materials may be absorbed by a variety of mechanisms. Depending on the nature of the material and the site of absorption, there may be passive diffusion, filtration processes, faciHtated diffusion, active transport and the formation of microvesicles for the cell membrane (pinocytosis) (61). EoUowing absorption, materials are transported in the circulation either free or bound to constituents such as plasma proteins or blood cells. The degree of binding of the absorbed material may influence the availabiHty of the material to tissue, or limit its elimination from the body (excretion). After passing from plasma to tissues, materials may have a variety of effects and fates, including no effect on the tissue, production of injury, biochemical conversion (metaboli2ed or biotransformed), or excretion (eg, from liver and kidney). 

Hematopoietic (blood) cells transport oxygen and carbon dioxide, contribute to host immunity, and facilitate blood clotting [1], A complex, interrelated, and multistep process, called hematopoiesis, controls the production as well as the development of specific marrow cells from immature precursor cells to functional mature blood cells. This well-regulated process also allows for replacement of cells lost through daily physiologic activities. The proliferation of precursor cells, the maturation of these into mature cells, and the survival of hematopoietic cells require the presence of specific growth factors. 

The most important product of the hexose monophosphate pathway is reduced nicotinamide-adenine dinucleotide phosphate (NADPH). Another important function of this pathway is to provide ribose for nucleic acid synthesis. In the red blood cell, NADPH is a major reducing agent and serves as a cofactor in the reduction of oxidized glutathione, thereby protecting the cell against oxidative attack. In the syndromes associated with dysfunction of the hexose monophosphate pathway and glutathione metabolism and synthesis, oxidative denaturation of hemoglobin is the major contributor to the hemolytic process. 

Most cytokines act upon, or are produced by, leukocytes (white blood cells), which constitute the immune and inflammatory systems (Box 8.1). They thus play a central role in regulating both immune and inflammatory function and in related processes such as haematopoiesis (the production of blood cells from haematopoietic stem cells in the adult bone marrow), as well as in wound healing. Indeed, several immunosuppressive and anti-inflammatory drugs are now known to induce their biological effects by regulating production of several cytokines. 

Many cytokines play a regulatory role in processes other that immunity and inflammation. Neurotrophic factors, such as NGF and BDNF, regulate growth, development and maintenance of various neural populations in the central and peripheral nervous system. EPO stimulates the production of red blood cells from erythroid precursors in the bone marrow. 

Magnesium is an important element that acts as a catalyst in many hfe processes. In addition to photosynthesis, it is also required for the oxidation in animal cells that produce energy and for the production of healthy red blood cells. Humans cannot hve without magnesium— which we acquire mainly from various foods. 

A viral etiology has been implicated in Burkitt s lymphoma, and there is some evidence that Epstein-Barr virus causes infectious mononucleosis in Europe and Burkitt s lymphoma in Africa. It has been suggested that if the cause of the Burkitt s lymphoma is viral, then entry of the virus particles into the lymphoid colls of the body may derange a part of the cell immune process, subsequently affecting the production of the IgM antibody, a theory which is compatible to the dysproteinemia sometimes seen in multiple myeloma and other lymphomas (N2). Also in support of this is the observation that C-reactive protein was markedly elevated in the serum of patients with Burkitt s lymphoma, and disappeared entirely from the blood when they were cured (MIO). The relationship between malarial infection and Burkitt s lymphoma has been dealt with in a previous section on malaria. 

Millions of our blood cells die and are replaced every day. The production system for these critical cells Is an orchestrated process of growth and development of specialized cells from Immature precursors, driven by protein factors. This only happens once we are adults. The general process is named for the differentiation—the change from an unspecialized ceii to a speciaiized cell able to do a job because of the presence of particular proteins. 

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. 

Mechanism of Action An anabolic steroid that promotes tissue-building processes, increases production of erythropoietin, causes protein anabolism, and increases hemoglobin and red blood cell volume. Therapeutic Effect Controls metastatic breast cancer and helps manage anemia of renal insufficiency. 

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