What types of stem cells are found in adults?
Adult/Somatic Stem Cells Introduction
Adult stem cells, also known as somatic stem cells, are a type of undifferentiated cell found in various tissues in the body. They are characterized by their ability to self-renew or reproduce themselves and to differentiate into multiple cell types within the tissue in which they are found. Adult stem cells play a vital role in maintaining and repairing tissues and organs throughout the body.
Unlike embryonic stem cells, which are derived from the inner cell mass of a blastocyst, adult stem cells are found in fully developed tissues. They have a more limited ability to differentiate compared to embryonic stem cells. Still, they can be obtained from adult tissue without the ethical concerns associated with the use of embryonic stem cells.
Several different types of adult stem cells have been identified in various tissues, including hematopoietic stem cells in the bone marrow, mesenchymal stem cells in the bone marrow and fat, neural stem cells in the brain, epithelial stem cells in the skin and other epithelial tissues, liver stem cells in the liver, and cardiac stem cells in the heart. Adult stem cells are being studied for their potential use in a wide range of therapeutic applications, including repairing damaged tissues and organs, treating autoimmune diseases, and replacing cells lost due to injury or disease.
Stem cells: What they are and what they do
Types of Adult/Somatic Stem Cells
Several types of adult stem cells have been identified in various tissues in the body, including:
1- Hematopoietic Stem Cells
Hematopoietic stem cells (HSCs) are rare cells of mesodermal origin found in the adult mammalian bone marrow that sit atop a hierarchy of progenitors that become increasingly restricted to multiple or single lineages. True HSCs remain mostly dormant in adult tissue and give rise to short-term HSCs with limited self-renewal capacity (6-8 weeks). When a short-term HSC transitions from an undifferentiated self-renewing state, it can become a common myeloid progenitor (CMP) or a common lymphoid progenitor (CLP) (CLP). Erythrocytes, monocytes and macrophages, neutrophils, basophils, eosinophils, megakaryocytes/platelets, and dendritic cells derived from the myeloid lineage. Osteoclasts are also derived from monocyte/neutrophil hemopoietic cells. T- and B-lymphocytes, as well as Natural Killer cells, are produced by the lymphoid lineage.
2- Mesenchymal Stem Cells
The majority of mesenchymal stem cells (MSCs) are found in the stroma of bone marrow. MSCs derived from bone marrow can naturally differentiate into mesodermal tissues such as muscle, tendon, adipocyte, osteocyte, and chondrocyte lineages. MSCs have been discovered in adipose tissue, intestinal stroma, the corneal limbal stroma of the eye, the trachea, and the dental pulp. MSCs are primarily found in niches near these tissues’ pericyte area of capillaries. Neonatal tissues such as the placenta, cord blood, and Wharton’s jelly are also important medical sources of MSCs. MSCs are used in the regenerative processes of adult tissues, such as the heart, after an infarction. MSCs may directly differentiate into particular cells from damaged tissues and serve as paracrine regulators of healing processes.
3- Intestinal Stem Cells
ISCs are multipotent stem cells that can differentiate into all types of differentiated cell types of the small intestine and colon (including the predominant enterocytes (absorptive cells); mucus-secreting Goblet cells; peptide hormone-secreting enteroendocrine cells; and Paneth cells).
4- Neuronal Stem Cells
The neural stem cells, also known as neural progenitor cells, are found in two distinct brain regions. In lateral ventricles, one population is located in the ventricular-subventricular zone. According to the mouse model, this population is primarily responsible for regenerating neurons in the olfactory bulb. The second population is located at the hippocampus’s interface of the hilus and dentate gyrus.
5- Stem Cells of Epidermis and Hair Follicle
The skin is divided into two layers: dermis and epidermis. The epidermis contains stem cells in charge of repairing and maintaining the epithelial barrier, which changes every 2-4 weeks. The dermis is made up of connective tissue and contains hair follicles, sweat glands, and blood vessels.
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