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Skibiel (3)
Lecture

SKIN.docx

3 Pages
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Department
Biology
Course Code
BIOL 2500
Professor
Skibiel

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Description
SKIN • Bodys biggest organ • Surface area ~ 20 square feet • Number of cells lost/minute: 40000­50000 o ~9 lbs of cells every year • found in cell • skin renews every~35 days: byy the time you’re 20, your skin has been replaced  200 times Integumentary system o skin­ cutaneous membrane (ET & CT) o integumentary system: skin, hair, nails, and glands • functions of integumentary system o barrier­ protects from bacteria, uv rays. Water o regulates body temperature o makes vitamin d  o excretes waste o sensory­ lots of sensory receptors • regions of the skin o epidermis (cutaneous membrane/skin) o dermis (cutaneous membrane/skin) o hypodermis (superficial fascia)  not technically part of the skin • cells of the epidermis o keratinocytes­ produce keratin (tough protein) o melanocytes­ make pigment melanin (skin color, uv protection) o dendritic cells­ immune function o tactile cells­ sensory receptors for touch  • epidermis *4­5 layers depending on body location o (deep)stratum basale (germinativum)  “basale layer”  deepest layer  single layer of cuboidal or columnar epithelial cells • actively mitotic • daughter cells pushed up into stratum spinosum • most destined to become keratinocytes • some migrate into dermis to form epidermal derivatives  (hair, nails, and glands)  also contain melanocytes (10­25%) o stratum spinosum  “prickly layer”  many layers of keratinocytes joined by desmosomes  melanin granules   dendritic cells o stratum granulosum  “granular layer”  4­6 layers of keratinocytes  first step of keratinozation occurs here • cells flatten • nucleus and organelles break down • accumulate granules • cells die  o stratum lucidum  “clear layer”  2­3 layers of dead flat keratinocytes  only seen in palms and soles o (superficial)stratum corneum  “horny layer”  20­30 layers of dead, flat keratinocytes filled with keratin  prevents water loss and protects underlying layers from  abrasion • evolutionary theory of skin color o melanin= pigment (red to yellow to brownish  black) o diff
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