Reduction of the number and size of parenchymal cells of an organ or its parts which was once normal is called atrophy.

CAUSES.

Atrophy may occur from physiologic or pathologic

Physiologic atrophy.

Atrophy is a normal process of aging in some tissues, which could be due to loss of endocrine stimulation or arteriosclerosis.

For example:

• Atrophy of lymphoid tissue in lymph nodes, appendix and thymus.
• Atrophy of gonads after menopause.
• Atrophy of brain with aging.

Pathologic atrophy.

1. Starvation atrophy.

• First depletion of carbohydrate and fat stores followed by protein catabolism.
• General weakness, emaciation and anaemia

2. Ischaemic atrophy.

Gradual diminution of blood supply due to atherosclerosis may result in shrinkage of the affected organ e.g.

• Small atrophic kidney in atherosclerosis of renal artery.
• Atrophy of brain in cerebral atherosclerosis.

3. Disuse atrophy.

Prolonged diminished functional activity is associated with disuse atrophy of the organ e.g.

• Wasting of muscles of limb immobilised in cast.
• Atrophy of the pancreas in obstruction of pancreatic duct.

4. Neuropathic atrophy.

Interruption in nerve supply leads to wasting of muscles e.g.

• Poliomyelitis
• Motor neuron disease
• Nerve section.

5. Endocrine atrophy.

Loss of endocrine regulatory mechanism results in reduced metabolic activity of tissues and hence atrophy e.g.

• Hypopituitarism may lead to atrophy of thyroid, adrenal and gonads.
• Hypothyroidism may cause atrophy of the skin and its adnexal structures.

6. Pressure atrophy.

Prolonged pressure from benign tumours or cyst or aneurysm may cause compression and atrophy of the tissues e.g.

• Erosion of spine by tumour in nerve root.
• Erosion of skull by meningioma arising from piaarachnoid.
• Erosion of sternum by aneurysm of arch of aorta.

7. Idiopathic atrophy.

There are some examples of atrophy where no obvious cause is present e.g.

• Myopathies.
• Testicular atrophy.

MORPHOLOGIC FEATURES.

• The organ is small, often shrunken.
• The cells become smaller in size but are not dead cells.
• Shrinkage in cell size is due to reduction in cell organelles
• There is often increase in the number of autophagic vacuoles containing cell debris.
• These autophagic vacuoles may persist to form ‘residual bodies’ in the cell cytoplasm e.g. lipofuscin pigment granules in brown atrophy