This document describes the 5 types of cell adaptation; atrophy, hypertrophy, hyperplasia, dysplasia and neoplasia. It then goes on to describe what happens to the cell when altered environmental conditions are too prolonged/severe, how injury can be identified and the different types of necrosis t...
There are particular environmental conditions under which cells operate best (depending on cell
type). For example, there will be a temperature, pH level and water level at which a cell operates
best under – these can be defined as the cell’s optimal conditions. However, these conditions are
not always met, and the cell must be able to adapt in order to cope. If these altered conditions are
too severe or prolonged, this could result in cell injury then cell death.
There are 5 different types of cell adaption; atrophy, hypertrophy, hyperplasia, metaplasia and
dysplasia. All cell adaptations re potentially reversible (in practice), as cells will revert back to their
original state once adverse conditions are removed. Adaptations can be physiological (due to normal
body processes) or pathophysiological (due to a disease process).
Cell Adaptation
Here I will describe each of the 5 cell adaption types and provide examples for each.
Atrophy
In cellular atrophy, cell size decreases therefore the tissue gets smaller as well. The cells contain
fewer organelles including mitochondria. This conserves energy.
Atrophy may result from malnutrition and ischaemia.
It can also result from disuse atrophy, where the skeletal muscle decreases in size due to a lack of
use. Disuse atrophy may occur in a patient with a broken limb and also occurs in astronauts who
experience a zero-gravity environment.
Another example of atrophy is denervation atrophy, where there is decreased stimulation by the
nervous system. Denervation atrophy could be a result of polio, where there has been a viral
infection causing the death of motor neurones in the spinal cord. In this particular case, the
adaptation is not reversible because we cannot repair the motor neurones to stimulate the tissue
once again.
Cerebral atrophy can be seen in patients with Alzheimer’s disease. Here, there is a loss of grey
matter density due to a lack of nerve cell connectivity and deeper grooves in the brain can be seen.
Atrophy may result from a lack of hormonal stimulation. For example, testicular atrophy may occur
due to steroid abuse. There are elevated levels of testosterone, meaning the testicles no longer have
to produce as much themselves. This causes them to decrease in size.
Hypertrophy
Hypertrophy is where the cell size increases and there is an increase in the number of organelles,
meaning larger tissue size. There can be skeletal hypertrophy and cardiac hypertrophy.
In cardiac hypertrophy, the ventricular wall thickens due to chronic hypertension. An increase in
blood pressure has meant the heart needs to work harder, increasing the size of the cardiac muscle.
This is beneficial up until a certain point, as the thickening of the ventricular wall causes narrowing
of the ventricular space, making the heart less effective.
Another example of cellular hypertrophy can be seen with the removal of a kidney. When a kidney is
removed, the remaining one will enlarge to compensate.
There can be hypertrophy of the smooth muscle in the bladder if there is a blockage to the outflow
of urine (e.g. enlarged prostate). This is to compensate for the increased difficulty of urinating.
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