TISSUE REPAIR

Restoration of tissue architecture & Function After an injury is referred to as REPAIR or HEALING.
REPAIR occurs by two processes
1. REGENERATION: Restores normal cells. occurs in tissue with Cells having capacity to proliferate
2. SCARRING: Connective tissue deposition, occurs in tissue with Cells without having capacity to proliferate or if the tissue is severely damaged ( In tissues with cells having proliferative capacity)

Two important aspects to be known in repair process are
1. Proliferation of cells– which is driven by growth factors. Stem cells also gives rise to mature cells.
2. Interaction between cells & Extracellular matrix (ECM)

The various cell types which proliferate during repair process are
a. Remnants of injured tissue: Attempt to restore normal tissue
b. Vascular Endothelial cells: Creates blood vessels for nutrition during repair
c.Fibroblasts: Forms scar and also For defects which cannot regenerate

Different types of tissues in the body based on Intrinsic proliferative capacity of the cells
1.Labile (Continuously dividing) tissue: Cells continuously being lost and replaced
Eg: Hematopoietic cells of BM & surface epithelia
2. Stable tissue: Cells Quiscent (G 0 Phase). Minimal proliferative activity & Divide in response to injury/loss. Eg Parenchyma of solid tissue Endothelial cells, fibroblasts , smooth muscle
3. Permanent tissue: Terminally differentiated. Nonproliferative in postnatal life. Eg Neurons Cardiac muscle,Skeletal muscle.

Proliferation of cells is by SIGNALS provided by
1. Growth factors: Produced by cells near the site of damage Eg Macrophages, Epithelil or stroma cells.
2. Extracellular matrix. Growth factors are bound to ECM proteins.Activate signaling pathways that stimulate DNA replication

Mechanism of Tissue regeneration ( regeneration of liver)

LIVER REGENERATION occurs by two processes
1. Proliferation of remaining hepatocytes
2.Repopulation from progenitor cells

The mechanism of cell proliferation occurs in three distinct  stages as illustrated in the figure below.

CLICK HERE to watch the video tutorial on Regeneration