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In The Name Of ALLAH, The Most Beneficent, The Most Gracious, The Most Merciful !. Anatomy & Physiology of Skin. PROF. MUHAMMAD ZAFAR M.B;B.S., M.PHIL., Ph.D. Functions of the Skin. Largest organ
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PROF. MUHAMMAD ZAFAR
M.B;B.S., M.PHIL., Ph.D.
Protection (Epidermis): against U/V light (melanocytes), physical barrier against friction, abrasion (keratinocytes), against desiccation (keratinocytes), relatively impermeable surface prevents water loss, barrier to invasion by microorganisms (thickness of epidermis & Langerhan’s cells by immune response), acts as first line of defence(Langerhan’s cells & other defence cells in the dermis), Elasticity is provided by the elastic fibers that allows for expansion of skin during pregnancy, swellings, edema etc., nails (protection)
Sensory receptor: (various types of receptors; PPTT)
Thermoregulation: (Heat loss and heat gain) By blood vessels, sweat glands and adipose tissue. Body insulation by the hairs and subcutaneous fat
Metabolic functions: subcutaneous adipose tissue is a store house of energy in the form of triglycerides, synthesis of vitamin-D in the epidermis by ultra-violet rays
Normal duration of maturation from basale to corneum is 50-60 days which is shortened to 7 days in Psoriasis.
In PSORIASIS,a common skin disease, there is an increase in the number of proliferating cells in the stratum basale & the stratum spinosum as well as a decrease in the cycle time of these cells. This results in the greater epidermal thickness and more rapid renewal of epidermis
Increased pigmentation of skin in Addison disease
Albinism, a hereditary inability of the melanocytes to synthesize melanin. Skin is not protected from solar radiation by melanin. There is greater incidence of basal & squamous cell carcinoma (skin cancers)
Vitiligo:Symmetrical areas of depigmentation associated with melanocyte destruction. It is auto immune
Moles or Naevi: Benign accumulation of melanocytes in dermis (intradermal naevus), epidermis (junctional naevus) or both (compound naevus)
Malignant melanoma: is a malignant tumour of melanocytes
In adults. 1/3 of all tumors are of the skin.
1. Basal cell carcinoma from stratum basale cells
2. Squamous cells carcinoma fro stratum spinosum
Both above types can be diagnosed early and can be excised.
3. Malignant Melanoma is lethal and highly invasive tumor of the melanocytes which penetrate the basement membrane, enter the dermis and invade the blood and lymph vessels to gain wide distribution throughout the body
A basement membrane separates the epidermis from the papillary dermis. It consists of three layers
It helps to bind epidermis to dermis
Abnormalities of the dermal-epidermal junction can lead to one type of blistering disorder (bullous pemphigoid). Another type of blistering disorder (pemphigus) is caused by the loss of intercellular junctions between keratinocytes.
In old age, excessive cross-linking of collagen fibers, the loss of elastic fibers and the degeneration of these fibers cause the skin to become more fragile, lose its suppleness, and develop wrinkles. The degeneration of elastic fibers is accelerated by excessive exposure to sun light.
Hairs: Thermoregulation (heat conservation; less marked in humans), Display, goose flesh effect in animals
Sebaceous glands: Sebum provides water proofing of skin and hairs
Sweat glands; Merocrine (heat loss by evaporation of sweat which reduces body temperature, sweat also contains sodium, chloride urea etc; thus it is also a means of excretion). Apocrine (in humans no definite function; in animals scent production, used in territory marking and sexual attractant. Apocrine secretion is viscid & milky & becomes malodorous after the action of commensal bacteria. Myoepithelial cells contraction helps the expulsion of sweat from the secretory unit.
Nails: support the back of finger tips for holding or applying forces, cosmetic effect
Breast: Secondary sexual organs, milk feeding
A hair follicle + associated sebaceous gland + Arrector pili muscle= Pilosebaceous unit
Merocrine glands secrete sweat which play an important role in thermoregulation.