Functions include Protection Chemical Barriers Acid mantle UV barrier Physical

Functions include protection chemical barriers acid

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Functions include: Protection Chemical Barriers Acid mantle UV barrier Physical barriers Water barrier Tough and dry Biological barriers Langerhans’cells in epidermis Dermal macrophages Thermoregulation Cutaneous arteries and sweat glands Sensory functions Receptors for heat, cold, touch, pressure, vibration, & pain Vitamin D synthesis Blood reservoir (up to 5% of body’s blood volume) Absorption of lipids Excretion Some nitrogenous wastes, salts, alcohol, etc. Know the cell layers of the epidermis in order and know the functions Composed of keratinized stratified squamous epithelium Outer portion of the skin is exposed to the external environment and functions in protection Consists of four distinct cell types and four or five layers Cell types: Four or five distinct layers: Keratinocytes Stratum basale Melanocytes Stratum spinosum
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Tactile (Merkel) cells Stratum granulosum Dendritic (Langerhans) cells Stratum lucidum (only in thick skin) Stratum corneum Epidermis is made up of four or five distinct layers Thick skin contains five layers (strata) and is found in high-abrasion areas (hands, feet) Thin skin contains only four strata Stratum basale ( basal layer ) Deepest epidermal layer firmly attached to the dermis Consists of a single row of stem cells Actively mitotic Produces two daughter cells One cell journeys from basal layer to surface Takes 25–45 days Dies as moves toward surface One cell remains in stratum basale as stem cell Since cells undergo rapid division, its alternate name is stratum germinativum Melanocytes compose 10 – 25% of this layer Stratum spinosum ( prickly layer ) Several cell layers thick Cells contain weblike system of intermediate prekeratin filaments attached to desmosomes Allows them to resist tension and pulling Keratinocytes in this layer appear spikey, so they are called prickle cells Scattered among keratinocytes are abundant melanosomes and dendritic cells Stratum granulosum ( granular layer ) Thin - four to six cell layers Drastic changes in keratinocyte appearance occurs Cells flatten Nuclei and organelles disintegrate Accumulate two types of granules Keratohyaline granules (form keratin) Lamellated granules (waterproof) Granules cut off nutrients Cells above this layer die Too far from dermal capillaries Stratum lucidum ( clear layer ) Found only in thick skin Consists of thin, translucent band of two to three rows of clear, flat, dead keratinocytes Lies superficial to the stratum granulosum
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Stratum corneum ( horny layer ) Outermost layer 20–30 rows of flat, anucleated, keratinized dead cells Accounts for ¾ of epidermal thickness Though dead, cells still function to: Protect deeper cells from the environment Prevent water loss Protect from abrasion and penetration Act as a barrier against biological, chemical, and physical assaults Outermost cells are exfoliated Know the cell types and the functions of the cell types found in the epidermis Keratinocytes
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