3. SKIN: Physiology & Function
• Epidermis:
– protective barrier (against mechanical damage,
microbe invasion, & water loss)
– high regenerative capacity
– Producer of skin appendages (hair, nails, sweat &
sebaceous glands)
4. SKIN: Physiology & Function
• Dermis:
– mechanical strength (collagen & elastin)
– Barrier to microbe invasion
– Sensation (point, temp, pressure, proprioception)
– Thermoregulation (vasomotor activity of blood
vessels and sweat gland activity)
5. SKIN: Physiology & Function
• Immunological surveillance
• Most skin is thin, hair-bearing, has sebaceous
glands
• Skin of palms/soles/flexor surface of digits is
thick, not hair-bearing, no sebaceous glands
• Vascular supply confined to dermis
14. Skin Grafts: “Process of Take”
• Plasmatic Imbibition:
– Initially graft ischaemic (24 – 48 hrs)
– Fibrin adhesion
– Imbibition allows the graft to survive this period
– ? Important for nutrition of graft
– ? Stops drying out
15. Skin Grafts: “Process of Take”
• Inosculation & capillary ingrowth:
– At 48 hrs
– Through fibrin layer
– Capillary buds from recipient bed contact graft
vessels
– Open channels (neo-vascularization)
pink graft
16. Skin Grafts: “Process of Take”
• Revascularization & fibrous attachment:
– Connection of graft & host vessels via anastomoses
(inosculation)
– Formation of new vascular channels by invasion of graft
(neovascularisation)
– Combination of old & new vessels (revascularisation)
– Fibroblast proliferation: conversion of fibrin adhesion
fibrous tissue attachment (anchorage within 4 days)
18. Skin Graft Take: Epidermis
Days Histological changes
0–4 Epithelium doubles; crusting, scaling of epidermis;
swelling of nuclei & cytoplasm; epithelial cell
migration to surface; mitosis of follicular & granular
cells
3 ++ mitotic activity in SSG not FTSG
4–8 Proliferation & thickening of epithelium (up to 7x)
desquamation
Week 4 Epidermis returned to normal thickness
19. Skin Graft Take: Epidermis
Day Histochemical changes
4 Increased RNA in basal cells, indicating protein
synthesis
10 RNA returns to normal
20. Skin Graft Take: Dermis
• Fibrous component:
Collagen Hyalinized early and progressively replaced
with new fibres by 6 weeks;
Turned over 3-4X faster than normal skin.
Elastin Accounts for resilience;
Days 3-7 fragment;
Replaced 4-6 weeks.
Extracellular Proteins direct the behaviour of
matrix keratinocytes;
Communication between keratinocytes &
fibroblasts.
21. Skin Graft Take: Dermis
• Appendages:
- sweating dependent on no. of transplanted sweat glands &
degree of sympathetic reinnervation; will sweat like recipient
site in FTSG only
- sebaceous gland activity mostly in thicker grafts: SSG usually
dry & shiny
- hair grows from FTSG if well taken with no complications
22. Skin Graft Healing
• Initially white then pinkens with new blood
supply
• Lymphatic drainage by day 6
• Collagen replacement from day 7 to week 6
• Vascular remodelling for months
23. Skin Graft Healing
• Contraction:
- shrinks immediately due to elastic recoil: – FTSG
40%; medium SSG 20%; thin SSG 10%.
- secondary contracture as heals:
- FTSG remains same size after above shrinkage;
- SSG will contract as much as possible;
- more dermis = less contraction
- ? Due to myofibroblasts
24. Skin Graft Healing
• Reinnervation:
– from margins to bed;
– 4/52 to 2 years;
– Depends on graft thickness and bed;
– Uneventful healing leads to near normal 2PD;
– Cold sensitivity can be a problem.
25. Skin Graft Expansion
• Based on principle that wounds
reepithelialized from the periphery
• Expansion provides larger areas from which
epithelium can grow
• Larger areas can be covered with less skin
26. Skin Graft Expansion
• Meshing
- covers large area
- easier to contour
- fluid can drain through holes
- cosmetic results less than ideal
- various mesh ratio
27. Skin Graft Survival
• Meticulous technique
• Atraumatic graft handling
• Well vascularized bed
• Haemostasis
• Immobilization
• No proximal constricting bandages
