Integumentary System Chapter 5: The Skin

Integumentary System A. Consists of cutaneous membrane (skin) & accessory structures 1. cutaneous membrane *epidermis-superficial *dermis- underlying area of 2. accessory structures- hair, nails, exocrine glands, in dermis 3. hyperdermis (subcutaneous layer) lies beneath the dermis

3. functions: protection from impact and abrasion excretion of salts & water Maintain temp- insulation or evaporation vitamin D synthesis & nutrition storage detection of touch, pressure, pain

B. Epidermis- consists of stratified squamous epithelium 1. avascular, rely on diffusion 2. active cells are near basal lamina due to short diffusion area. 3. Superficial cells are inert or dead. a. dominated by keratinocytes, form several layers, full of keratin 4. Types a. Thin skin- consists of 4 layers of keratinocytes, covers most of body b. thick skin -5 layers covers palms of hands and soles of feet c. Provides mechanical protection, prevents fluid loss, and protection from microorganisms

C. Layers of Epidermis 1. Stratum germinativum- inner most epidermal layer, cell division takes place, replacing superficial cells 2. Cell pass through:  stratum germinativum (base layer)  stratum spinosum (spiny layer)  stratum granulosum(grainy layer)  stratum lucidum (only in thick skin, clear layer)  stratum corneum (exposed surface) 3. Cells accumulate keratin during process, and eventually are shed. Process takes days, w/ dead exposed cells remaining in s.corneum for 2 more weeks. Remember: g ermy s piney g ranny l ooks c orny

4. Epidermal ridges- formed from the interlocking stratum germinativum and underlying dermis, which has projections ( dermal papillae )  provide ridges on palms and soles  increase skin’s sensitivity  ridge pattern is unique, doesn’t change during one’s lifetime, basis of finger prints 5. stratum. germinativum is dominated:  basal cells- stem cells whose divisions replace keratinocytes that are shed  Merkel cells provide sensory info about objects that come in contact w/ the skin  melanocytes provide pigment 6. Dendritic cells (Langerhans) in stratum spinosum stimulate defense against microorganisms and superficial skin cancers

Section 5.2 A. Pigments in epidermis 1. Carotene and melanin a. Carotene is orange-yellow pigment that can be converted to vitamin A- needed for epithelia maintenance and eyes b. melanin- brown, yellow-brown, or black pigment, made by melanocytes in the s. germinativum and transfer pigments to keratinocytes

c. Melanin protects dermis and epidermis from effects of sun’s UV radiation-protect DNA d. Melanin increase in production in response to increase in exposure to sun, but synthesis is slow, so burns often occur 2. Dermal circulation gives dermis a reddish tint a. hemoglobin is bright red when bound to oxygen b. lack of oxygen can cause change in skin color- bluish color (cyanosis) c. jaundice- yellow color, liver is unable to excrete bile d. vitiligo- individuals lose their melanocytes (MJ)

5.3 B. sunlight causes cells in s. spinosum and s. germinativum to convert a steroid in the epidermis to Vitamin D. 1. liver converts Vitamin D into a product used by the kidneys to synthesize the hormone calcitrol - which is needed for the absorption of calcium and phosphorus (not enough leads to impaired bone growth/ maintenance---rickets)-avoided w/ fortified milk 2. vitamin- nutrient that must be obtained from diet because body can’t make or doesn’t make enough

5.4 C. Epidermal Growth Factor (EGF)- a peptide growth factors 1. promotes the division of germinative cells in s. germinativum and s. spinosum 2. accelerates keratin production 3. stimulates repair after injury