Skip to content
Explore atlas
PH-FD17

Atrophy

Why cells and organs shrink when use, nerve supply, blood supply, hormones or nutrition fall: how a cell digests its own proteins, the main causes of atrophy, what atrophic organs look like and when the change can reverse.

By the end, you can

  • Define atrophy and distinguish it from hypoplasia, aplasia and cell death.
  • Explain how a cell shrinks by breaking down its own proteins and organelles.
  • Relate the main causes of atrophy (disuse, denervation, reduced blood supply, pressure, loss of hormones, poor nutrition, ageing) to examples.
  • Describe the gross and microscopic appearance of atrophic organs, including brown atrophy.
  • Explain when atrophy can reverse and what it costs the organ.
  • Recognise the classic appearances and tests of atrophy, including brown atrophy and denervation atrophy, and explain how restoring use, nerve supply, nutrition, hormones or blood supply reverses it.

What it is

Atrophy is a reduction in the size of a cell, and so of a tissue or organ, after it has reached its normal size. The cells shrink and, as it continues, some are lost. It is an adaptation: a smaller cell needs less oxygen and fuel and can survive on less. It differs from hypoplasia and aplasia, in which an organ never developed fully. Atrophy can be physiological (the thymus after childhood) or pathological, and general (the whole body, as in cachexia) or local (one organ or limb).

3 types to tell apart
Physiological atrophy
Part of normal life: the thymus shrinks from adolescence, the uterus after childbirth, and the breast, ovaries and endometrium after the menopause.
General atrophy (wasting, cachexia)
The whole body wastes, in starvation or in chronic disease such as advanced cancer, chronic infection or heart failure. Fat and skeletal muscle are lost first; the brain is relatively spared.
Local atrophy
One organ or region shrinks, from disuse, denervation, reduced blood supply, pressure or loss of hormonal stimulation.

US spelling: fibre → fiber, fibres → fibers.

Normal function

Cell size matches demand

A cell keeps its size by balancing two processes: building proteins and organelles, and breaking them down. Use, an intact nerve supply, growth signals such as insulin and insulin-like growth factor 1 (IGF-1), and an adequate supply of oxygen and nutrients keep building level with breakdown.

Skeletal muscle shows the balance well. Each is a single long cell filled with contractile proteins, striped by its and , with its at the edge and between the fibres. Regular use and a working motor nerve keep the fibres at their working size; training enlarges them.

Some shrinkage is normal. The thymus shrinks from adolescence, the uterus returns towards its former size after childbirth, and hormone-dependent tissues shrink after the menopause. This is physiological atrophy.

Point to it on the model