Basic Sciences Relevant to Plastic Surgery (Anatomy, Physiology, Wound Healing, Pathology)
What this domain tests
The board examines basic science only where it changes a decision: which plane to dissect, which wound will heal, which lesion needs a margin. Expect stems that link a structure, a healing phase, or a histological pattern to a clinical consequence.
Skin architecture and tension lines
- Epidermis renews about every 28 days and carries no adnexae; split-thickness grafts re-epithelialise from retained dermal appendages of the donor site, which is why a thin graft takes better but contracts more.
- Dermis is predominantly type I collagen in the reticular layer; papillary dermis is finer, type III-rich. A scar that stays type III and hypercellular is immature.
- Relaxed skin tension lines run perpendicular to the underlying muscle. Langer lines are cadaveric and should not be equated with RSTL in life.
Vascular anatomy
Angiosomes (Taylor) are three-dimensional blocks fed by a source artery, connected by reduced-calibre choke vessels; a perforasome is the territory of one perforator. Delay works by conditioning choke vessels; it does not create new arteries.
Wound healing timeline
- Haemostasis: platelet plug, fibrin, vasoconstriction.
- Inflammation (0–3 days): neutrophils first; macrophages dominate from day 3 and drive the transition through PDGF and TGF-beta.
- Proliferation (3 days–3 weeks): fibroblast collagen synthesis, angiogenesis, granulation; keratinocytes migrate about 1 mm/day; myofibroblasts contract.
- Remodelling (3 weeks–1 year and beyond): collagen III is replaced by type I, cross-links increase. Tensile strength is about 5% at 1 week, 20% at 3 weeks, and 70–80% by 6 months - never 100%.
Modifiers and pathology
Hypoxia below roughly 30 mmHg tissue oxygen, smoking, corticosteroids (blunted inflammation and TGF-beta), diabetes, radiotherapy (obliterative endarteritis), and vitamin C or zinc deficiency all impair healing. Basal cell carcinoma is the commonest skin cancer, with basaloid palisading and perineural spread in morpheaform variants; squamous cell carcinoma arises on sun-damaged or scarred skin, and a chronic ulcer in an old scar is a Marjolin ulcer. Melanoma prognosis is stratified by Breslow thickness, not diameter.
Worked example
A 2 cm circular wound on a diabetic shin should epithelialise from both edges at 1 mm/day - 10 mm per edge, roughly 10 days. At 6 weeks the wound is still 1.7 cm. Reasoning: epithelialisation alone would have closed a defect of this size; persistence means failure of contraction and granulation from ischaemia and glycation. Wounds larger than about 4 cm, over a joint, or in a poorly perfused bed should be excised and grafted rather than observed.
Traps
- Stating mature scar collagen is type III.
- Quoting 100% tensile strength.
- Equating Langer lines with RSTL.
- Attributing steroid impairment only to infection, ignoring blunted inflammation and fibroblast function.
- Grading melanoma risk by surface size.