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Integumentary SystemWednesday, October 10, 201212:21 PMSkin - Integument/Cutaneous membrane*Skin is largest organ of the body Integumentary - skin & skin accessories Skin Structures:-Sweat (sudoriferous) glands-Sebaceous (oil) glands-Hair & Hair follicles-Nails Epidermis (Top layer 20% of skin)Dermis (Next Layer)Hypodermis (Not part of the skin) Thickness = 1.5-4mm2 Basic Types (based on thickness of epidermis):-Thin skin - 4 strata-Thick skin - 5 strata - found in palms & soles, areas subjected to stress (abrasion) Deepest -->- Stratum Basale (Stratum Germinativum)-keratinocytes - cuboidal epithelial cells that undergo mitosis to produce cells for superficial strata)-melanocytes produce melanin as a chemical shield from UV rays, (more melanin = more protection)-constant exposure to sunlight can break down chemical shield-melanin is contained in vesicles called melanosomes --> inside melanocytes-merkel cells - crescent-like shape associated with nerve endings in the papillary layer of the dermis, associated with nerve endings that form structures called merkel discs (act as touch-receptors)*Merkel cells do not act as touch receptors (merkel discs do)-Stratum Spinosum-cells connected by desmosomes-Tonofilaments present to withstand pulling forces placed on the skin-Langerhans' cells provide immunity, act as macrophages (engulf/digest pathogens)-epidermis is avascular, therefore macrophages in the blood stream do not have access to epidermis-Stratum Granulosum-[Stratum Lucidum] - thick skin only -composed of dead, translucent layers of cells (adds to thickness)-palms & soles - areas of skin subjected to the most stress-Stratum Corneum-most superficial layer, dead cells-cells are "cornified" - dead cells impregnated with keratin (released from the keratohyaline gowwles) and coated with glycolipids (released from the lamellated granules) DERMISAccounts for 80% of the entire thickness of the skin2 Layers:-Papillary layer (superficial)-Composed of areolar CT (highly vascularized - to provide nutrients to the overlying avascular epidermis)-Surface had peg-like projections called Dermal Papillae (Houses: Meissner's Corpuscles (touch receptors), Nerves (free nerve endings), & blood capillaries)-in thick skin, dermal papillae form Dermal Ridges (larger, deeper projections) that make impressions on the surface of the epidermis called Epidermal Ridges (friction ridges that make it possible to pick up/grasp small objects from surfaces) - epidermal ridges are 'partially' genetically determined (fingerprints), however the way we manipulate the environment can modify the pattern.-Sweat glands open up along the epidermal ridges and a film of sweat is left on solid surfaces touched bythe fingers/toes --> basis for finger-printing-Reticular layer (deep)-Composed of dense irregular CT (highly vascularized - to provide nutrients to the overlying avascular epidermis)-80% of the thickness of the dermis Nervous Structure in the Skin:-Merkel discs - respond to light touch-Meissner's Corpuscles - act as touch receptors-Root hair plexus - around hair follicles-Pacinian Corpuscles - respond to deep pressure Accessory structures in the skin --> all derived from the stratum basale (keratinocytes) but all reside in the dermis --> dermis is highly vascularized and provides nutrients to accessory structures *Accessory structures are all derived from the epidermis but reside in the dermis Accessories in the Skin:-Sweat Glands-Acidic Mantle - acidic pH of sweat that prevents microbial growth on the surface of the skin-sudoriferous glands, simple coiled tubular multicellular exocrine glands-Merocrine (via exocytosis), 2 types: Eccrine & ApocrineFunction:1. Excretion of metabolic wastes2. Immunity (against pathogens) - lmmune globulin A & dermicidis3. Thermoregulation - sweat is released when the core body increases --> evaporation of sweat from skin using heat from the body to cool the body 4. Sweat has a low pH (acidic) which prevents microbial growth on surface of the skinApocrine Sweat Glands - become active after puberty (stimulated by sex hormones), associated with body odor "Odoriferous" glands SEBACEOUS GLANDS:-simple alveolar glands-secretes sebum using the holocrine mode of secretion-three things can result: 1.) whiteheads 2.) blackheads 3.) acne-two kinds: 1.)structural= simple aveolar 2.) functional= holocrine mode of secretionHAIR (PILI)/ HAIR FOLLICLES:-has two regions: 1.) shaft= region above the skin and on the scalp 2.) root= region below skin and enclosed by the hair follicle -hair follicles contain the hair matrix *hair matrix is composed of highly mitotic cells that produce new cells to replace shed cells from the hair-in cross section (transverse cut), hair may appear round which indicates straight hair *oval looking hair indicates wavy hair *flat looking hair indicates curly hair- in cross section (regardless of shape) we can identify three regions: 1.) outer cuticle= composed of a single layer of overlapping cells - this layer of overlapping cells protects cells in the cortex and the medulla -damage to cuticle-> exposes cells in the medulla and cortex and is referred to as split ends -damaged hair conditions can prevent split ends by protection to the cuticle which reinforces the overlapping called of the cuticle 2.) middle cortex 3.) inner medulla-the root may also have some metabolic waste that comes through-hair is also referred to as pili-hair follicles with its enclosed hair root approaches the surface of the skin at an oblique angle *hence, the shaft of the hair appears at an oblique on the surface of the skin-attached to the hair follicle is the arrector pili muscle (“hair raiser”) *this is smooth muscle *it contracts when environmental temperature falls (when its cold) *when the muscle contracts, it pulls the hair follicle and hence, the hair from an oblique position to a straight (right angle) position -the hairs are now standing upright forming a trap= a thin layer of cold air on the surface of the skin which acts as an insulator to prevent heat loss from the bodyNAILS:-they are scale-like modifications of the stratum corneum located on the distal ends, on the dorsal of thedigits (fingers and toes)-functions: 1.)protects the ends of the digits 2.)for grasping/ gripping small objects 3.)scratching-> dislodge pathogens trying to gain access into the skinFUNCTIONS OF THE SKIN:


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UMD BSCI 201 - Integumentary System

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