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Morphological adaptations observed at the cellular level include atrophy, hypertrophy, hyperplasia, and metaplasia. [1] In the medical context, outside of specialized branches of biomedicine , morphological adaptations are not always referenced to the fundamental cellular level, but are observed and assessed at the level of tissues and organs .
Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. [1] It is distinguished from hyperplasia , in which the cells remain approximately the same size but increase in number. [ 2 ]
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.
Cerebral atrophy is a common feature of many of the diseases that affect the brain. [1] Atrophy of any tissue means a decrement in the size of the cell, which can be due to progressive loss of cytoplasmic proteins. In brain tissue, atrophy describes a loss of neurons and the connections between them.
The muscle hypertrophy may persist throughout the course of the disease, or may later atrophy, or become pseudohypertrophic (muscle atrophy with infiltration of fat or other tissue). For instance, Duchenne and Becker muscular dystrophy may start as true muscle hypertrophy, but later develop into pseudohypertrophy. [41]
Microscopically, cells resemble normal cells but are increased in numbers. Sometimes cells may also be increased in size (hypertrophy). [7] Hyperplasia is different from hypertrophy in that the adaptive cell change in hypertrophy is an increase in the size of cells, whereas hyperplasia involves an increase in the number of cells. [8]
Eccentric hypertrophy is generally regarded as healthy, or physiologic hypertrophy and is often termed "athlete's heart." It is the normal response to healthy exercise or pregnancy, [6] which results in an increase in the heart's muscle mass and pumping ability. It is a response to 'volume-overload', either as a result of increased blood return ...
Neurological causes include radiculopathy, poliomyelitis, Charcot-Marie-Tooth disease, spinal muscular atrophy. [2] In pseudohypertrophy where the atrophied muscle tissue has been infiltrated by fat tissue, upon palpitation the seemingly large muscles feel doughy. [3] Not all muscles infiltrated by fat or other tissue are pseudohypertrophic.