Question

Whether healing will take place by regeneration or by repair (scaring) depends partly on the type of cell in the damaged organ and destruction or the intactness if the stromal frame work of the organ. Discuss.

Answer 1

All living beings encounter every kind of traumatic event from a small paper cut to myocardial infarction and heal the damaged tissues. The recovery of tissue damage consists largely of tissue repair rather than pure regeneration. Wound repair is a normal and complex biological process in the human body occurring in all types of tissues and organs. Tissue repair consists of two separate processes: regeneration and replacement. Regeneration is a type of healing in which new growth completely restores the damaged tissue to their normal state. Replacement is a type of healing in which severely damaged or non-regenerable tissues are repaired by the laying down of connective tissue, a process commonly referred to as scarring. For example some minor paper cuts sometimes can be healed in such a way that no permanent damage remains. Sometimes the original structures of the damaged tissue (e.g., the healing of a myocardial infarction) may result in structural abnormalities so that a scar formed.

The wound healing by the regeneration or the replacement pathway depends on the type of tissue in which it occurs. Some tissues are capable of cellular proliferation or regeneration. There are three types of tissues which are capable of proliferation or regeneration. They are continuously dividing tissues (labile tissues), quiescent tissues (stable tissues) and non-dividing tissues. Continuously dividing tissues contain constantly proliferating cells in order to replace dead or damaged cells. Examples of continuously dividing tisues include epithelia (such as skin, gastrointestinal epithelium and salivary gland tissue) and hematopoietic tissues. All these tissues contain pools of stem cells, which have the ability to proliferative and regenerate. The stem cells have the ability to give rise to more than one type of cell. The quiescent tissues are composed of cells that normally exist in a non-dividing state but may enter the cell cycle in response to cell injury. Examples of quiescent cells are parenchymal cells of the liver, kidney and pancreas, fibroblasts and smooth muscle cells (mesenchymal cells), endothelial cells and lymphocytes. Unlike other quiescent tissues, the liver cells have a relatively robust proliferative capacity. When a lobe of the liver is resected for donation, the remaining liver cells proliferate at such a rate that the liver reaches a size similar to that prior to resection. While this process is commonly described as regeneration, it is more accurately viewed as compensatory growth, since the original lobe itself does not regrow. Non-dividing tissues are composed of cells that have left the cell cycle permanently and do not proliferate. These non-dividing tissues (permanent tissues) include cardiac and skeletal muscle. Tissue repair in these tissues always leaves permanent evidence of injury, such as a scar.