Hypodermis (subcutis, superficial fascia)
Hypodermis & appendages · Adipose lobules Fibrous septa Stage 3 pressure injury
Lobules of adipocytes separated by fibrous septa that carry the vessels and nerves supplying the skin above. It insulates, stores energy, cushions bony prominences and is the plane used for subcutaneous injection.
Traced from the start
- Stratum basale (germinativum)
- Lamina densa (type IV collagen basement membrane)Sublamina densa anchoring fibrils (type VII collagen)
- Papillary dermis
- Reticular dermis
- Hypodermis (subcutis, superficial fascia)
Detail
- Structure
- Fat lobules divided by connective tissue septa through which the perforating vessels and nerves reach the deep dermal plexus
- Functions
- Thermal insulation, mechanical cushioning over bony prominences, energy storage, and endocrine secretion of leptin and adiponectin
- Injection plane
- Subcutaneous injection (insulin, low-molecular-weight heparin) gives slower, more sustained absorption than intramuscular; adrenaline for anaphylaxis must be intramuscular into the anterolateral thigh, not subcutaneous
- Beneath it
- Deep fascia, then muscle and bone — the tissues whose exposure defines a stage 4 pressure injury
When it goes wrong
Septal panniculitis without vasculitis (erythema nodosum)
Tender nodules on the shins that resolve without ulceration or scarring; look for streptococcal infection, sarcoidosis, inflammatory bowel disease, tuberculosis, pregnancy, the combined oral contraceptive or sulfonamides
Repeated insulin injection into the same subcutaneous site
Lipohypertrophy with erratic, unpredictable absorption and unexplained glycaemic swings; corrected by site rotation
Polymicrobial or group A streptococcal infection tracking along the fascial plane beneath the fat (necrotising fasciitis)
Pain out of proportion to the findings, systemic toxicity and rapid progression; the treatment is urgent surgical debridement, not antibiotics alone
Practise this structure
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