F. Tissue Regeneration and Repair
Tissue repair is the replacement of worn-out, damaged, or dead cells . New cells originate by cell division from the stroma (the supporting CT), or from the parenchyma (cells that constitute the functioning part of the tissue or organ). Each type of tissue (epithelial, connective, muscle, nervous) have a different capacity to replenish parenchymal cells lost by disease, damage, or other processes. Epithelial cells which endure considerable wear and tear have a continuous capacity for renewal. Some connective tissue also has a continuous capacity for renewal (example: bone due to its excellent blood supply). Muscular tissue has a fairly poor capacity for renewal. Nervous tissue has the poorest capacity for renewal. In the above renewal processes, immature, undifferentiated cells called stem cells divide to replace lost or damaged cells. Most of the tissues above have revealed some stem cells present. The restoration of an injured tissue or organ to normal structure and function depends entirely on whether parenchymal cells are active in the repair process.
Tissue Regeneration:
If Parenchymal cells accomplish the repair, a near-perfect reconstruction of the injured tissue may occur. This is tissue regeneration.
Tissue Replacement Fibrosis:
If Fibroblasts of the stroma are the active part of the repair, the replacement tissue will become new connective tissue ultimately forming scar tissue. This impairs the original function of the tissue or organ. In cases of extensive damage (large open wounds), both parenchyma and stroma become involved in repair by a process called Granulation . All the processes of both the parenchyma and stroma create a growing CT called Granulation Tissue. The new tissue forms across the wound or surgical incision providing a framework (stroma) that supports epithelial cells to migrate into the open area and fill it. The newly formed granulation tissue also secretes a fluid that kills bacteria.
Factors affecting tissue repair include:
1) Adequate nutrition is vital including adequate protein because most of the structural components of a tissue are protein. Vitamins play a key role in wound healing. For example: Vitamin C affects the normal production and maintenance of matrix materials, especially collagen, and strengthens promotes the formation of new blood vessels.
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