Hematopoiesis process

Hematopoiesis— process by which blood and blood cells are formed Hematuria—blood in the urine... 

Deficiency. Macrocytic anemia, megaloblastic anemia, and neurological symptoms characterize vitamin B 2 deficiency. Alterations in hematopoiesis occur because of the high requirement for vitamin B 2 for normal DNA repHcation necessary to sustain the rapid turnover of the erythrocytes. Abnormal DNA repHcation secondary to vitamin B 2 deficiency produces a defect in the nuclear maturational process of committed hematopoietic stem cells. As a result, the erythrocytes are either morphologically abnormal or die during development. 

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 cellular elements of the blood have a short life span and must be continuously replaced. The formation of red blood cells, white blood cells, and platelets, collectively, is referred to as hematopoiesis. This process takes place in the red bone marrow. In adults, red bone marrow is found in the pelvis, ribs, and sternum. 

As with the development of other organ systems, the development of the immune system is a highly regulated process. Table 19.1 and Figure 19.1 provide a list of known events or markers that occur during immune system development. In humans, hematopoiesis begins at approximately 3-4 weeks of gestation with the development of blood... 

In addition to erythrocytes, blood contains white blood cells, called leukocytes, of several types, and platelets, also called thrombocytes, which control blood clotting. Hematopoiesis (from the Greek, haimo, for blood, and poiein for to make ) is the process by which the elements of the blood are formed. The marrow of bone contains so-called stem cells which are immature predecessors of these three types of blood cells. Chemicals that are toxic to bone marrow can lead to anemia (decreased levels of erythrocytes), leukopenia (decreased numbers of leukocytes), or thrombocytopenia. Pancytopenia, a severe form of poisoning, refers to the reduction in circulatory levels of all three elements of the blood. One or more of these conditions can result from sufficiently intense exposure to chemicals such as benzene, arsenic, the explosive trinitrotoluene (TNT), gold, certain drugs, and ionizing radiation. Health consequences can range... 

Abkowitz JL, Catlin SN, Guttorp P. Evidence that hematopoiesis may be a stochastic process in vivo. Nat Med. 1996 2 190 197. 

From this description it is clear that this new cell is a highly specialized feature and this rises an interesting question of what was the primary reason for development of such a cell in the fish, where bones are not resorbed and colonized by the hematopoiesis. There is no experimental answer to this question yet, but speculation on that subject should concentrate on other requirements for bone resorption that would be of an immediate necessity for the fish. Such other requirement is tooth eruption. Without teeth fish would be unable to eat most of the food available, and to defend itself, so their eruption is of critical importance for survival. With emergence of calcification of bones during their development teeth had it increasingly more difficult to erupt and this required development of mechanism to assist in this process. So the hypothesis based on this speculation is, that the osteoclasts emerged primarily to assist tooth eruption. 

The last potential mechanism to be discussed in this chapter is drug-induced altered receptor expression. Hematopoiesis is a very intricate process that is regulated by cytokines and cell-cell interactions. Interruption with any of these processes can result in hematotoxicity. For example, zidovudine (AZT) decreases Epo [27], GM-CSFaand to lesser extent IL-3 receptor expression [7]. Decrease in the expression of the above receptors seems to lead to anemia and neutropenia, by decreasing the number of CFU-E and CFU-GM, respectively. 

Hematopoiesis, the process of generating mature blood cells, is mainly located in the red bone marrow, predominantly in the sternum, femur and pelvic bones [1]. In the marrow the hematopoietic cells are embedded in stromal tissue. This consists of different cell types (e.g., fibroblasts, endothehal cells, adipocytes, macrophages) that provide soluble and membrane-bound growth factors and produce an extracellular matrix consisting of collagen, laminin, fibronectin, and glycosaminoglycans [2, 3]. The interactions between hematopoietic cells, stromal cells and extracellular matrix are indicated in Fig. 1 [4,5]. 

As outhned earUer every single step of hematopoiesis is regulated and controlled in vivo by the cell s microenvironment. This not only includes the composition and concentration of growth factors, but also the local oxygen concentration, the pH, the osmolaHty, the supply of nutrients and the cellular and molecular surrounding of the cells (cell-cell contact, adhesion molecules and extracellular matrix). All these parameters affect the fate of the cell and, to estabUsh a cell culture process to cultivate or generate a specific subpopulation, the influence of all these factors has to be considered in the experimental set-up. In the following sections these parameters will be discussed in brief. 

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. 

Hematopoiesis, the production from undifferentiated stem cells of circulating erythrocytes, platelets, and leukocytes, is a remarkable process that produces over 200 billion new blood cells per day in the normal person and even greater numbers of cells in people with conditions that cause loss or destruction of blood cells. The hematopoietic machinery resides primarily in the bone marrow in adults and requires a constant supply of three essential nutrients—iron, vitamin B12,... 

Hematopoiesis is the process generating bloodcells. It takes place mainly in the bone marrow. 

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... 

Intrahepatic cholestasis caused by mechanical obstruction is also common, but is rarely associated with jaundice or with visibly dilated ducts on imaging studies, although it may be associated with increased direct bilirubin. Jaundice typically occurs only with lesions that are very large, or are located near the porta hepatis, where they may obstruct both hepatic ducts. Common causes of intrahepatic obstruction include (1) tumors (particularly metastases), (2) granulomatous diseases (such as sarcoidosis and tuberculosis), and (3) infiltrative processes (such as lymphoma, leukemia, and extramedullary hematopoiesis). 

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