Topic – Regeneration & adaptation

Regeneration It is the process of healing by proliferation of parenchymal cells , results in complete restoration of original tissues

Proliferation & differentiation • Proliferation may be defined as the expansion of cells by the continuous division of single cells into two daughter cells.

• Differentiation is the process whereby an undifferentiated cell, e.g. a stem cell, acquires the features of a specialized cell.

The Relationship Between Proliferation and Differentiation

• Proliferation occurs prior to differentiation.• Without proliferation, differentiation would not occur.• Differentiation is a default program requiring prior proliferation. But the corollary is not true.

• If proliferation is affected by a drug or other agent or perturbation, then differentiation will also be affected, but not visa versa

Classification 

Physiologic  Reparative 

Pathologic 

Surgical wound healing

Keloid

Dysplasia

Adaptation • an adaptation, also called an adaptive trait, is

a trait with a current functional role in the life of an organism that is maintained and evolved by means of natural selection.

• Adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation.

• The developmental norm of reaction for any given trait is essential to the correction of adaptation as it affords a kind of biological insurance or resilience to varying environments.

Kinds of adaptive

processes • Atrophy • Hypertrophy or hyperplasia• Organization • Reconstruction • Metaplasia• Dysplasia

Atrophy • Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations (which can destroy the gene to build up the organ), poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, excessive amount of apoptosis of cells, and disuse or lack of exercise or disease intrinsic to the tissue itself.

•  In medical practice, hormonal and nerve inputs that maintain an organ or body part are said to have trophic effects. A diminished muscular trophic condition is designated as atrophy.

• Atrophy is the general physiological process of reabsorption and breakdown of tissues, involving apoptosis. When it occurs as a result of disease or loss of trophic support due to other disease, it is termed pathological atrophy, although it can be a part of normal body development and homeostasis as well.

Kinds of general atrophy 

• Alimentary cachexia • Tumoral cachexia • Hypophysear cerebral cachexia • Toxic cachexia 

Kinds of Local atrophy 

• Dysfunctional or disuse atrophy• Atrophy due to hypo circulation• Atrophy due to high pressure • Neurotrophic atrophy  • Atrophy under the influence of physical and chemical factors 

Atrophy of hepatocytes

Brown atrophy of heart

Hypertrophy

Organization 

• Replacement of necrosis or clot with the connective tissue

• Encapsulation • Petrification

Reconstruction=

hyperplasia +

Regeneration +

Accommodation

Compensation • Compensatory growth is a type of regenerative growth that can take place in a number of human organs after the organs are either damaged, removed, or cease to function.

•  Additionally, increased functional demand can also stimulate this growth in tissues and organs. The growth can be a result of increased cell size (compensatory hypertrophy) or an increase in cell division (compensatory hyperplasia) or both.

•  For instance, if one kidney is surgically removed, the cells of other kidney divide at an increased rate. Eventually, the remaining kidney can grow until its mass approaches the combined mass of two kidneys