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Intergumentary system Premed II
Integumentary System Skin and its epidermal derivatives such as nail, hair, sweat gland, sebaceous gland and mammary gland. Epidermis is an epithelial layer of ectodermal origin. Morphometry of skin: - largest and heaviest organ– 1.2 to 2.3 m2 ;16% of the total body weight in adults. - thickness varies form 1mm to 5mm; - thickest over the back; thinnest in the eyelid
epidermis Gross histology: - two types : - non-hairy (thick or glabrous or smooth skin) found in palm and sole - hairy or thin skin – covering most of the body surface - two layers : epidermis, dermis - supported and anchored to subcutaneous tissue – hypodermis (subcutis) dermis
Basic Histology of Skin Epidermis - the superficial layer - keratinised stratified sqamous epithelium; well developed in nonhairy skin - five layers in non – hairy skin: from deep to superficial - stratum basale or germinativum - strat. spinosum - strat. granulosum - strat.lucidum (not found in hairy skin) - strat. Corneum L
Dermis - connective tissue arranged in two strata: - superficial papillary layer - deep reticular layer
Dermatoglyphics Finger Prints and Foot Prints • -true dermal ridges in palmar and plantar skin having parallel arrangements • - genetically determined • unique for each individual • corresponding epidermal ridges are seen on the surface as loops, arches, whorls or combinations of these forms
Dermato glyphics Unique for each individual , appearing as loops, arches and whorls or combinations of these form. Probably determined by multiple genes. Used for person identification . ***medico-legal purposes.
Epidermis Stratum basale • Single layer of columnar cells rest on basal lamina • stem cells for new cells- as the outer cells are shed continuously- so the name germinativum(intense mitotic activity.) Str. basale
Stratum Spinosum Stratum Malpighii = str. basale + str spinosum -cuboidal or polyhedral cells, exhibit numerous cytoplasmic extensions (spines) so the name.
Stratum Granulosm • 3 to 5 layers thick; polyhedral cells • contains keratohyalinn granules.
Stratum Lucidum • translucent layer (seen in thick skin) • flattened cells • cytoplasm packed with keratin granules
Water barrier function- an attribute of epidermis • -skin is impermeable to water / any soluble and non soluble substances • “keratosomes” (lamellar bodies) in the granulosa cells contain water repellant glycolipid • In the deeper part of st. corneum, the tonofibrils, keratin along with the non- wettable glycoprotein form intercellular cement to provide a sealing effect for the skin
Cells of Epidermis • Keratinocytes • Melanocytes • - Langerhan cells • Merkel’s cells • Kerartinocytes: • epidermal cells that arise from the basal layer. • secretion forms the extracellular water barrier.
Melanocytes • - pale, round cells in the basal layer • neural crest in origin • -synthesizes melanin from tyrosine in the presence of tyrosinase • synthesis occurs in membrane bound granules – premelanosomes • melanin is transferred into the cells of str.basale and str. spinosum through cytocrine secretion.
Colour of skin is the result of several factors,the most important of which are the content of melanin and carotene,number of blood vessels in the dermis . Eumelanin is a dark brown pigment produced by the melanocyte, a specialised cell of the epidermis found beneath the cells of the str. Basale and in the hair follicles. CLINICAL ANATOMY: PSORIASIS -A common skin disease There is increase in number of proliferating cells in the str. Basale and spinosum as well as a decrease in the cycle time,. This results in greater epidermal thickness and more rapid renewal of epidermis----7 days ,instead of the regular 15-30 days.
Although melanocytessythesize melanin ,epithelial cells act as a depot and contain more of this pigment. ALBINISM: -- hereditary inability of melanocytes to sythesizemelanin. Melanocytessythesize a dark brown pigment(melanin) in oval shaped organelles(melanosomes). Melanosomes contain tyrosinase, a UV- sensitive enzyme involved in melanin synthesis. HYPERPIGMENTATION: --lack of cortisol from the adrenal cortex, causes overproduction of ACTH, which increases the pigmentation of the skin. Addison”s disease is caused by dysfunction of the adrenal glands** VITILIGO: --the degeneration and disappearance of the entire melanocyte results in a depigmentation disorder. MALIGNANT MELANOMA: -major env. factor is the sun or UV light. ***pheomelanin***is less protective against UV radiation damage.
Dermis • connective tissue ; supports and binds epidermis to subcutaneous tissue • Papillary layer: loose ; fine collagen fibres; contain Meissner’s corpuscle • Reticular layer: coarse collagen bundles irregularly arranged; elastic fibres
Appendages of Skin • skin appendages are embryologically derived from surface epidermal ectoderm • hair follicle • sebaceous gland • sweat gland • -nail, -mammary gland
Function of Skin • barrier function – protects external biological and non biological toxic agents • homeostatic function – regulating heat loss and water loss • sensory function- specialised for touch, pain, heat sensation • secretory function - conversion of precursor molecule into vitamine D using solar radiation • ? Lipid soluble substance may be absorbed
Dermal fibroblasts: synthesize ground substance & fibres Langer lines: lines of cleavage or tension lines - formed by definitive orientation of fibres in the dermis - a cut in the skin parallel to Langer lines will heal fast with minimal scar - a linear wound perpendicular to Langer lines will tend to gape and heal slowly with conspicuous scar.
Blood Circulation • specialised for nutrition for skin appendages and thermoregulation • - irrigation from subcutaneous blood vessels • Two pleuxes of vessels: • subcutaneous plexus: • at the junction of dermis with superficial fascia – supply deep dermis, glands and hair follicle • subpapillary plexus: • at the junction of epidermis and dermis – supply superficial dermis and epidermis by diffusion • arterio- venous anastamoses: numerous for thermoregualtion- open in cold condition & closed in hot condition • Lymphatics : rich lymphatics ; form plexuses as the blood vessels
Sebaceous Gland • simple branched acinar gland ; holocrine secretion; • duct: with stratified squamous epithelium; open into the hair follicle; the sebum gradually moved to the surface of the skin • - acini formed by a basal layer of flattened cells with cytoplasmic organelles for synthesis of sebum (deeper acinar cells are large polyhedral cells with abudant sER and lipid granules).
A holocrine gland-----the products are secreted with the remnants of dead cells,stem cells at the base of the gland proliferate to replace lost cells. The products comprises of a complex mixture of lipids that includes:triglycerides ,waxes ,squalene, and cholesterol and its esters. Sebaceous gland begins to function by puberty,the primary control of sebaceous gland secretion in men is testosterone and in females a combination of ovarian and adrenal androgens. Medical application: Flow of sebum is continuos, and a disturbance in the normal secretion and flow of sebum is one of the reasons for development of a chronic inflammation of obstructed sebaceous glands. **it occurs mainly during puberty**
Arrector pili muscle • – bundle of smooth muscle fibres attached to the hair follicle just below sebaceous gland; • extends to and attached to dermal papillae; contraction causes secretion of sebum into the hair follicle and movement of sebum to the surface; erection of hair • under sympathetic control ; piloerection is activated by cold and fear • in furry animals hair erection helps to trap air over the skin – a mechanism to increase the insulation against heat loss
Glands of moll and the ceruminuous glands???? Where are these glands found??