Integumentary System Wednesday October 10 2012 12 21 PM Skin 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 4mm 2 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 DERMIS Accounts for 80 of the entire thickness of the skin 2 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 by the 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 Apocrine Function 1 Excretion of metabolic wastes 2 3 Thermoregulation sweat is released when the core body increases evaporation of sweat from Immunity against pathogens lmmune globulin A dermicidis 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 skin Apocrine 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 secretion HAIR 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 body NAILS they are scale like modifications of the stratum corneum located on the distal ends on the dorsal of the digits 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 skin FUNCTIONS OF THE SKIN 1 thermoregulation hot weather increase in environmental temperature eccrine glands to produce more seat and evaporation of sweat using heat from the body cools the body reflex sweating cold weather decrease in environmental temperature action of the arrector pili muscle prevents heat loss from the body Protection a Physical protection skin acts as a
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