الفهرس 
Introduction and Aim of the workOnly 14 pages are availabe for public view
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Abstract
Stem cells are unspecialized small, round cells with squat nucleus and scanty surrounding cytoplasm, they can act as biological resurrection. Stem cells have two major features, self-renewal and ability to differentiate into mature cells. It can reproduce forever. Types of stem cells: Totipotent: Directly issued from the zygote divisions from the embryo, from day 0 to 4. Pluripotent: Give rise to all human tissue cells ”about 200 cell types”. It is the cell which is capable to differentiate into the three somatic germ layers that comprise an organ ectoderm endoderm and mesoderm. Multipotent: Is the cell which can give rise to any of the three germ layers. Sources of stem cells: Fetal stem cell: are often taken from the germ line tissues that will make up the ovaries or tests of aborted featus. Umbilical cord blood contains stem cells similar to those found in the bone marrow of new born. Placenta derived stem cells. Embryonic stem cells. Adult stem cells: tissues like bone marrow, lung, pancreas, brain breast, fat, skin contain stem cells. Stem cell plasticity is its ability to change its phenotypic characteristics ”transdifferentiation”. Plasticity means reprogramming in response to external factors. MSCs are typically isolated from stromal fraction of adult bone marrow. MSCs are capable of forming osteoblasts, chondrocytes and adipocytes. Osteogenic potential osteogenic differentiation of MSCs is induced in vitro by treating a monolayer culture with a pro-osteogenic coklaol. Osteogenic potential of MSCs have utilized to treat cases of defective fracture healing, both alone and in combination with scaffolds to repair. * Adipogenic potential: Formation of mature adipocytes occurs following treatment of MSCs with a specific medium. * Myogenic potential: MSCs have been demonstrated to have the ability to form muscle cells. * Neural potential MSCs can form neural cells. * Stem cell and kidney disease: Conflicting data had been reported about the differentiation of bone-marrow derived cells into renal tubular cells. It is now generally accepted that stem cells and multipotent cells contribute to the regenerative process by producing protective and regenerative factors rather than by directly differentiating to replace damaged cells. * Cardiac stem cells: The notion that the adult heart is terminally differentiated organ without self-renewal potential has been undermined by the existence of a subpopulation of replicating myocytes in normal and pathological states. Cardiac infusion of MSC triggers the formation of new cardiomyocyte and neoangiogensis in the human heart. It is still unclear wether MSC act directly in situ differentiation or fusion with resident myocyte or indirectly through secretion of promyogenic factors promoting endogenous myocardial repair. Any how the existence of these cells opens apportunilies for myocardial repair. Transplantation of BM hematopoietic stem cells can result in with generate of functional hepatocyets. Stem cell plasticity is linked to the harvesting and culturing of adult stem cells. Their multipotential and transdifferential capabilities could be utilized in treating a number of disorders including stroke, burns of skin, spinal cord injuries, degenerative disorders, Parkinsom and Alzheimer’s disease and chronic disease such as diabetes, heart failure and liver failure. Stem cells from one tissue could change their fate and give rise of cells of different types. This phenomenon is called transdifferentitaion. So, cells from neural tissues can be transformed into hematopoietic cells under stress conditions. The key factor in the formation of self-renewing cellular clones is the presence of stem cells either from the tissue of origin or stem cell migrating from other areas and successful to settle in an empty niche of the damaged tissue. Stem cells will play a key role in cell therapy. Experimental biology and medicine have used stem cells in cell therapy for more than 20 years. Applications of stem cells: The availability of autologous MSCs, which are easily accessible from patients, makes them a promising source of cells for many clinical applications in the evading filed of regenerative medicine. MSCs represent an advantages cell type for allogenic transplantation as evidence suggests that MScs are immune-privileged, with low MHCI and MCHII expression, therefore reducing risks of rejection and complications.