Hyperplasia

• Increase in cell number
• Occurs in response to a stimulus, will regress if the stimulus is withdrawn
• e.g. lymph nodes, liver regeneration, smooth muscle
• In some circumstances carries a low risk of neoplastic transformation (i.e. the growth becomes autonomous)

Hypertrophy

• Increase in cell size
• e.g. skeletal muscle, left ventricular hypertrophy

Atrophy

• Loss of size and/or number of cells
• Occurs on withdrawal of a stimulus - hormonal or mechanical
• e.g. being bed bound, wearing a cast

Metaplasia

• Reversible change of one mature cell type to another mature cell type in response to injury
• e.g. Barrett’s oesophagus - stratified squamous to columnar epithelium

Neoplasia

• New cell growth with no stimulus
• Can be benign, pre-malignant (dysplastic and still benign) or malignant
• e.g. squamous papilloma - benign neoplastic growths with no malignant potential

Dysplasia