What are stem cells?

What Are Stem Cells?

• What are Stem Cells? Where do scientists get them from (in the human body)? What do scientists use them for? Whats the difference between embryonic stem cells and adult stem cells?

• Answer:

  The gametes merge to become a zygote. Cleavage from the large initial zygote produces a ball of totipotent cells, then a hollow sphere of small pluripotent blastula cells, in mammals. Cell fates are determined so inner embryoblast cells are dedicated to become the fetus while trophoblast cells now become the membranes, umbilical cord and placenta. These trophoblast structures are a source of embryonic stem cells. As the embryo developes, cells differentiate. Differentiation involves tissue specific gene regulation that results in pluripotent progenitors of cell lineages, resulting from the initial totipotent zygote. Each tissue type has a pattern of genes expressed in a regulated fashion that is its own subset of possible combinations of the whole genome. Each germ layer tissue type assumes an exact location and number of pluripotent cells. Regulation increases in daughter cells as tissue and later organ systems develop. Regulation increasingly blocks expression of inappropriate genes, it down regulates genes so cells eventually become multipotent or specialized stem cells that are retained throughout adult life. These adult stem cells can divide to produce organ specific cell types for normal function: replacement and repair. http://www.jyi.org/volumes/volume5/issue1/features/tusin.html Cell division can be symmetric producing duplicate daughter cells for simple growth or asymmetric producing distinctly different daughter cells for specialization of function. Stem cells divide asymmetrically so they both renew themselves and produce differentiated daughter cells. The unequal daughter cells provide a way for the organism to keep the stem cell progenitor cells and provide specialist cells so the body can grow and repair itself. Somatic stem cells renew body cell types The epithelial basal stem cells replaces skin cells. The gastrointestinal epithelial stem cell replaces the gut lining. Placental stem cells are one of the most interesting types since they seem to have no antigenic surface markers. http://www.sciencedaily.com/releases/2007/05/070503125732.htm The bone marrow has the Haematopoetic stem cells that can differentiate into the three major blood cell lineages: erythrocytes, platelets, & white cells (lymphocytes eukocytes, neutrophils, basophils, macrophages, etc.). The bone marrow also has mesenchymal stem cells (skeletal stem cells), which can become muscle, fat, cartilage, fibrous connective tissue or bone. http://www.csa.com/discoveryguides/stemcell/overview.php Corneal stem cells Neuronal/glial stem cell Mammary gland stem cells