I. Healing
Healing is accomplished either by proliferation of the parenchymal element of the injured tissue or by replacement of the damaged tissue with fibrous connective mu.. The former is called regeneration and the latter, repair.
There are three kinds of cells in human body; labile cells, stable cells, and permanent cells. Regeneration is confined only to the tissues ´containing the labile or stable cells, and the process consists basically of 1) proliferation of the original cells and migration of those cells into the damaged part, and 2) proliferation of the migrated cells.
Repair is categorized as healing by first intention and healing by second intention. Those two involve successively similar phenomena: 1) fibrinous union, 2) union by granulation tissue, 3) union by fibrous tissue, and 4) epithelial regeneration. However, in the healing by first intention scar tissue is scanty on the contrary to large scar tissue and cicatrical contraction of the wounds in the other.
Repair of fractures is somewhat different from the healing of soft tissue injuries in respect of callus formation and rearrangement of the callus. Though repair of the fractures is continuous process, it is divided conveniently into four steps depending on the length of time since injury. 1) Occurence of hematoma and traumatic inflammation, 2) Organization, 3) Union by callus,and 4) Rearrangement of callus and bony union.
During the regeneration of epithelium and connective tissue injured part is occasionally replaced by fully differentiated cells of different kind to the original tissue. in response to abnormal stimuli, such as transformation of pseudostratified ciliated columnar epithelium of respiratory tract to squamous type, columnar epithelium of the duct of salivary gland to squamous one, and transitional epithelium of urinary
|