Hypodermis

Function

The hypodermis — subcutaneous fat — is energy vault, thermal blanket and mechanical shock absorber in one. Its adipocytes' lipid droplets swell and shrink with the body's energy balance, and its lobular architecture dictates how infection spreads (along the septa as cellulitis) and how wounds gape.

Insulin is injected here because absorption is steady and slow; so are some vaccines (for example MMR), though most are given intramuscularly.

Blood supply

Perforating cutaneous arteries.

Nerve supply

Pacinian corpuscles in some regions sense deep pressure.

Clinical relevance

Necrotising fasciitis

Flesh-eating infection races along fascial planes beneath it — pain beyond findings demands surgical exploration.

Lipoma

The commonest soft-tissue tumour — a soft, lobulated, mobile mass of mature fat.

Related conditions

• Cellulitis