In The Name Of ALLAH, The Most Beneficent, The Most Gracious, The Most Merciful !

1. In The Name Of ALLAH,The Most Beneficent, The Most Gracious, The Most Merciful !

2. Anatomy & Physiology of Skin PROF. MUHAMMAD ZAFAR M.B;B.S., M.PHIL., Ph.D.

4. Functions of the Skin Largest organ 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

5. 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 • Excretion: urea & other metabolite through sweating • Repair& regeneration: By the stratum basale and fibroblasts & collagen fibers of the dermis • Secondary sex organ (sexual attractant): Breast & apocrine sweat glands • Dermatoglyphics:The patterns assumed by ridges & intervening sulci. Finger prints are unique for each individual • Route of drug absorption specially lipid solvents (epidermis)

6. Epidermis • Self regeneration----- helps in repair • Keratin ----- water resistant layer, provides a coating, repels water, protects from dryness, tolerates desiccation • Stratum Basale: continuous supply of cells by mitotic division • Stratum spinosum: synthesis of protein cytokeratin • Stratum granulosum: synthesis of Keratohyaline granules, presence of Odland bodies or keratinosomes which are water repellent

7. Contd. • Keratinocytes: produce keratin • Melanocytes: protects against U/V sunlight, gives colour to skin and hairs • Langerhans cells: protect against epidermal tumours, recognise and process external antigens, have a role in rejection mechanism in skin allografts • Merkle cells: Intraepidermal touch receptors. They are specialized touch receptors (mechanoreceptors).Some evidence suggests that they have functions related to diffuse neuroendocrine system • Rete ridges: Strongly tethering and offer resistance to frictional shearing forces

8. Medical applications regarding Epidermis 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

9. Medical application regarding Melanocytes 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

10. Medical application regarding Epidermis 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

11. Langerhans cells • They are antigen-presenting cells & are an important component of the immune defence mechanism. • Contact allergic dermatitis

12. Dermis • Dermis provides the tone & texture of skin. In adults skin is tight while in elderly skin wrinkles due to degeneration of fibers • Cellular component of the dermis is mainly fibroblasts which are responsible for the production of collagen & elastin, but lymphocytes, mast cells & tissue macrophages involved in non-specific defence are also present. • The collagen & elastic fibers form lines of tension called Langer Lines. • Fibroblasts play a major role in repair

13. Contd. • Collagen fibers provide the tensile strength. Their irregular arrangement helps to transmit forces exerted in different directions (like struts) • Elastic fibers provide elasticity to skin. Contraction of scar is by elastic fibers • Dermal papillae: Strongly tethering and offer resistance to frictional shearing forces • Arrector pili muscle: contraction cause erection of hairs for increased insulation, make animal look bigger; called goose flesh effects

14. Medical application regarding Basement Membrane A basement membrane separates the epidermis from the papillary dermis. It consists of three layers Lamina Lucida Lamina Densa Lamina fibroreticularis 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.

15. Medical application regarding Dermis 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.

16. Functions of skin circulation: • Nutrition of the skin and appendages • Increased blood flow to facilitate heat loss in hot conditions • Decreased blood flow to minimize heat loss in cold conditions • Numerous shunts provide direct arteriovenous communications which play an important role in thermoregulation by controlling blood flow to the appropriate part of the dermis.

17. EPIDERMAL APPENDAGES 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

18. A hair follicle + associated sebaceous gland + Arrector pili muscle= Pilosebaceous unit • Secret an oily substancesebum (lipids) by means of holocrine method • Sebum may have weak antibacterial & antifungal properties. It also acts as a water proofing & moisturizing agent for the hair & skin surface

19. Merocrine glands secrete sweat which play an important role in thermoregulation. • Apocrine glands produce a viscid, milky secretion which is discharged into the hair follicles and becomes malodorous after the action of skin commensal bacteria. Apocrine glands becomes functional at puberty & undergo cyclical changes in women

20. Sub-Cutis (sub-cutaneous tissue) • Shock absorption • Store house of energy in the form of triglycerides • Insulation • Thermoregulation (conserving heat) • In face contains muscle called muscles of facial expression (panniculus carnosus)