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What is Atrophy?

Meaning and Definition of Atrophy

The word atrophy comes from the Greek “ atrophía ” ( a – private ; trophe – nutrition ), which means lack of nutrition , withering. This is a term used in pathology and physiology , both at the cellular level, as well as at the tissue and organic level, in these cases it is synonymous with hypotrophy .

In this context, cell atrophy is the decrease in cell size due to loss of intracellular content. However, this condition does not lead to cell death, there is only a decrease in its volume.

Atrophy in organs and tissues can be classified as simple atrophy , due to the reduction in volume of a significant number of cells; and numerical atrophy, caused by a reduction in the number of cells.

What Can Cause Atrophy?

Atrophy can be caused by physiological or pathological factors . The former can be caused by aging or loss of hormonal stimulation, such as atrophy of the breasts, uterus, and ovaries after menopause. Reduction after childbirth of the additional volume of the uterus , acquired during pregnancy; and involution of the thymus and other lymphoid organs after puberty.

Pathological factors related to atrophy are:

Atrophy due to disuse or reduced workload

It occurs in cases where the limb is immobilized in recovery from bone fractures or due to loss of innervation, caused by nerve injuries.

by starvation

When the individual is fasting for a long time or in a poor nutritional state , there is a degradation of the internal content of the cell itself, as well as in the hypotrophy of adipose tissue, desired in weight loss or in the loss of muscle and bone mass due to malnutrition.

endocrine

Lack of certain factors can lead to glandular cell atrophy , as in injuries and diseases of the pituitary gland that trigger atrophy of the gonads, adrenal gland, and thyroid.

by pressure

The presence of tumors, cysts and aneurysms can compress the vessels, which leads to poor nutrition of an area, causing its atrophy.

Due to vascular loss

Some pathologies lead to a decrease in the local circulation of the organs, such as arteriosclerosis, which can cause brain atrophy.

How does atrophy occur?

Numerical atrophy of certain organs, such as the uterus after childbirth, occurs through mechanisms of cell death, specifically apoptosis.

Cell atrophy, on the other hand, occurs due to changes that trigger cell shrinkage , still with enough volume to survive, but adapted to the new condition that stimulated it. For example, the cell of a tissue with vascular deficiency reduces its volume and metabolism in a way adapted to the amount of nutrients provided by the current vascularization.

The main way the cell shrinks combines decreased protein synthesis and degradation of intracellular proteins. This process is orchestrated by the ubiquitin-proteasome pathway. In this way, lack of use or reduction of nutrients activates ubiquitin protein ligases, which bind to and degrade cytoplasmic proteins in proteasomes.

Another pathway that causes a reduction in cell volume during nutrient deprivation is autophagy. In it, external stimuli trigger the formation of autophagic vacuoles through the endoplasmic reticulum. This organelle is sequestered in vesicles, intracellular structures, and part of the cytosol.

These vesicles fuse with lysosomes, forming autophagosome , which undergo lysosomal degradation.

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