1. Epidermal wound healing Basal cells of epidermis surrounding wound break contact with basement membrane Enlarge and migrate across wound –EGF (Epidermal Growth Factor) stimulates basal stem cells to divide and replace migrating cells Stop migration due to contact inhibition Relocated cells divide to build new epidermal layers and thicken epidermis

2. Deep wound healing Deep wound healing occurs when injury extends to dermis and/or subcutaneous layer Four phases: –Inflammatory phase Blood clot forms loosely binding wound edges Inflammation –eliminates microbes, foreign material and dying tissue –enhances delivery of helpful cells –Migratory phase Clot becomes scab Epithelial cells migrate beneath scab to bridge wound Fibroblasts synthesize scar tissue (lots of collagen) Blood vessels penetrate scar tissue (forms granulation tissue)

3. Deep wound healing Four phases continued: –Proliferative phase Extensive growth of epithelial cells beneath scab Random deposition of collagen fibers Blood vessel growth –Maturation phase Epithelium restored to normal thickness and scab sloughs off Collagen fibers become more organised Fibroblasts decrease in number Blood vessels restored to normal

4. Deep wound healing Scar tissue differs from normal skin in so far as: –Collagen fibers more densely arranged –Fewer blood vessels –Fewer hairs, glands, sensory structures –Usually lighter in color than normal skin due to arrangement of collagen fibers and scarcity of blood vessels From: http://www.abateit.com/scar-pictures.htm

5. Aging Most age related changes occur in dermis –Wrinkling Collagen fibers decrease in number, stiffen, break apart, and form shapeless tangles Elastic fibres lose elasticity, thicken into clumps and fray Fibroblasts (produce collagen and elastin) reduce in number –Reduced skin immunity Langerhans cells reduce in number Macrophages become less efficient

6. Aging Sebaceous glands decrease in size –Results in dry, cracking skin more susceptible to infection Sweat production diminishes –Increased susceptibility to heat stroke Decrease in number of functioning melanocytes –Grey hair, change in skin pigmentation Some melanocytes enlarge producing age spots Migration of cells in epidermis from basal layer to corneum slows –Skin heals more slowly –More susceptible to pathology Growth of hair and nails slows –Nails may become more dry and brittle