The word healing, used in a pathological context, refers to the body’s replacement of destroyed tissue by living tissue.The healing process involves two distinct processes: Regeneration, the replacement of lost tissue by tissues similar in type and repair (healing by scaring), the replacement of lost tissue by granulation tissue which matures to form scar tissue. Healing by fibrosis is inevitable when the surrounding specialized cells do not possess the capacity to proliferate. Whether healing takes place by regeneration or by repair (scarring) is determined partly by the type of cells in the damaged organ & partly by the destruction or the intactness of the stromal frame work of the organ. Hence, it is important to know the types of cells in the body, based on their proliferative capacity there are three types of cells.
1. Labile cells
These are cells which have a continuous turn over by programmed division of stem cells. They are found in the surface epithelium ofthe gastrointestinal tract , urinary tract or the skin. The cells of lymphoid and haemopoietic systems are further examples of labile cells. The chances of regeneration are excellent.
2. Stable cells
Tissues which have such type of cells have normally a much lower level of replication and there are few stem cells. However, the cells of such tissues can undergo rapid division in response to injury. For example, mesenchymal cells such as smooth muscle cells, fibroblasts, osteoblasts and endothelial cells are stable cells which can proliferate. Liver, endocrine glands and renal tubular epithelium has also such type of cells which can regenerate. Their chances of regeneration are good.
These are non-dividing cells. If lost, permanent cells cannot be replaced, because they don’t have the capacity to proliferate. For example: adult neurons, striated muscle cells, and cells of the lens.