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a&p chap 5 Skin

a&p chap 5 skin

Functions of the skin ProtectionExcretionTemperature regulationSensory perceptionSynthesis of Vitamin D
Structure of the Skin and Hypodermis Thickest in areas subjected to wear and abrasionThinnest on eyelids, eardrums, and external genitalia
Epidermis Stratified squamous epitheliumContains no blood vessels or nerves, depends on dermis for vascular supplyServes as a boundary
Epidermis protects the body against Entrance of pathogens-Ultraviolet radiation-Excessive water loss
Stratum basale Innermost layer of epidermisSite of mitotic cell divisionNew cells move from the stratum basale towards the surfaceAs cells move they form distinctive layers in the epidermis
Stratum corneum Outermost layer – varies in thickness according to usageNumerous layers of dead, flat, keratinized cellsConstantly sloughed off and replaced
How long for for cells to complete their journey It takes approximately two weeks for new cell to complete their journey through the epidermisCells acquire keratin as they migrate through the epidermal layers
Dermis Composed of fibrous connective tissueCollagen: strength and toughnessElastic fibers: extensibility and elasticity
Dermal papillae Conelike projections of dermis that fit into recesses of epidermisLight touch receptors are closest to the epidermis, and perceive pressure, pain, heat, cold receptors are in deeper parts of the dermis
Dermal blood vessels are important for Supplying nutrients to epidermal cellsTemperature regulation
Hypodermis or subcutaneous layer Loose connective tissue and adipose tissue
Functions of Hypodermis Attaches skin to underlying tissues and organsSite for subcutaneous injectionsSite of white blood cell actionHeat insulatorFat storage – adipose tissueConserve body heat and retards penetration of external heat
Skin Color Skin color results from three different pigments. Hemoglobin, Carotene, and Melanin
Hemoglobin Red color from red pigment in red blood cells
Carotene Yellowish pigment in stratum corneum and dermis
Melanin Brown-black pigment formed by melanocytes in epidermisSurrounding epidermal cells pick up the melanin as it is produced
Amount of melanin that can be produced is inherited Greater production= darker color
Melanocytes are equally distributed Freckles – excessive build-up of melanin in one location
Duration of ultraviolet light exposure determines rate of melanin production
Skin color of various human races results from different amounts of carotene and melanin Effect of hemoglobin is relatively constantDark-skinned races: produce abundant melaninAsians: produce more caroteneCaucasians: produce relatively little melanin
Accessory Structures: Hair Formed by keratinized cellsMade of two partsShaftRootHair is found over most of the bodyFunctions to protect the body
Hair follicle Contains the hair rootBulb of follicle is site of new hair growthNourished by dermal papillaeNew cells from bulb become part of the root
Arrector pili muscle Contracts and raises the hair in the follicle on endCauses “goose bumps”
Accessory Structures: Nails On dorsal surface of fingers and toesMade of keratinized epidermal cellsColorlessStructuresBodyRootLunulaFunctions are protection and object manipulation
Accessory Structures: Glands Form from epidermis that grows inward into the dermis
Three types of integumentary glands Sebaceous glands - oilSudoriferous glands - sweatCeruminous glands – ear wax
Sebaceous glands Oil-producingEmpty sebum into hair folliclesFunctionsIncrease pliability and softness of skin and hairLimit evaporative water lossInhibit bacterial growth
Sudoriferous (Sweat) Glands Two types of sudoriferous glands. Apocrine sudoriferous glands and Eccrine sudoriferous glands
Apocrine sudoriferous glands Located in axillaries and genital regionsActivate at pubertyMilky sweat due to proteins and fatsOdorlessBO due to bacterial decomposition
Eccrine sudoriferous glands Occur all over the bodySecrete sweat onto skin surface directlyCleary, watery perspirationActivated with increase in body temperatureFunctions to cool the body
Ceruminous glands Produce cerumen (aka. ear wax)Found in external auditory canalKeeps foreign particles and insects out of auditory canal
Temperature Regulation Normal body temperature is maintained at 37C (98.6F)Skin plays a key role in conserving or dissipating heat to maintain temperatureHeat source is cellular respiration in metabolically active tissue
Loss of excess heat with an increase in body temperature Brain increases blood flow to skinHeat loss by radiationSweat glands begin to produce perspirationSweat evaporation accelerates heat loss
Heat conservation due to drop in body temperature Brain reduces blood flow to skinPrevents radiation heat lossSweat glands inactivateBrain stimulates skeletal muscles to “shiver” and generate additional heat
With age, skin becomes damaged due to harmful conditions SunlightWindAbrasionsChemical irritantsBacterial invasions
Typical changes in aging skin Breakdown of collagen and elasticDecrease in subcutaneous fatDecrease in sebum productionDecrease in melanin productionDecrease in hair replacement
Created by: 50611802