Healing

The word  healing, used in a pathological context, refers to the body’s replacement of destroyed tissue by living tissue.

Processes of healing

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.

Figure 1 Processes of healing: Removal of dead tissue & injurious agent and replacement occur simultaneously.

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.

Types of cells

 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 of the gastrointestinal treat, 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.

3. Permanent cells

These are non-dividing cells. If lost, permanent cells cannot be replaced, because they do not have the capacity to proliferate. For example: adult neurons, striated muscle cells, and cells of the lens. 

References

Bezabeh ,M. ; Tesfaye,A.; Ergicho, B.; Erke, M.; Mengistu, S. and Bedane,A.; Desta, A.(2004). General Pathology. Jimma University, Gondar University Haramaya University, Dedub University.