Stem cells are?

Ans. is A Labile o Based on their proliferative and regenerative capacity, cells are divided into:- 1) Labile cells (continuously dividing cells) or intermitotic cells # These cells have capacity to proliferate and regenerate throughout the life. They always remain in cell cycle and have very short Go-phase (quiescentphase). Example are:- i) Surface epithelium (stratified squamous) of skin, oral cavity, vagina and cervix. ii) Lining mucosa of all excretory ducts of glands (Salivary gland, pancreas, biliary duct). iii) Columinar epithelium of GIT (Intestinal mucosa) and uterus. iv) Transitional epithelium of the urinary tract. v) Bone marrow cells and hematopoietic cells. vi) Basal cells of epithelia. 2) Stable or quiescent or reversible postimitotic cells # They have limited capacity to proliferate and regenerate. They remain in Go phase of cell cycle but can enter in G1 phase when stimulated i.e., they usually remain quiescent, but proliferate in response to stimuli. Example are:- i) Parenchymal cells of liver, kidney and pancreas. ii) Mesenchymal cells, e.g., fibroblast and smooth muscles. iii) Vascular endothelium iv) Osteoblast, chondroblast v) Resting lymphocytes and other leukocytes. 3) Permanent or nondividing or irreversible postmitotic cells # They cannot divide and regenerate. These cells are nondividing and have left the cell cycle, i.e., they do not belong to any phase of cell cycle. Example are:- i) Neurons ii) Cardiac muscle iii) Skeletal muscle.