External Features of the Skin Epidermis Activity Do you remember what type of tissue this is? General: Epithelial Specific: Stratified Squamous Keritinized

Dissecting Scope or Stereoscope When properly put away, the fastener is around the cord. If you no longer have a fastener, wrap the cord around the arm and lock the male head around the cord.

Lights Turn on the main light. To observe the skin on your hand, do you think it would be better to use the top light or bottom light?

Magnification and Focusing You can magnify the image 2x or 4x. 2. You can raise the nose piece to assist with focusing.

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Structure determines function Characteristic Skin covering the back of the hand Skin covering the palm of the hand Why? Thickness Thinner Thicker More layers on the palm, provide more protection Calluses None Usually yes Friction promotes increased cell division Oily feel Oily Not oily Oils would result in reduced friction when gripping objects

Elasticity of skin Elastic- able to return to original form after a force is applied Why do you think the skin of the palm is more elastic than the back of the hand? What other objects can you think of that are elastic?

What factors reduce elasticity? Genetics Smoking UV radiation Stress- production of the stress hormone cortisol destroys collagen fibers (this hormone also causes breakouts.) Sleep- Repair of skin occurs when you sleep A diet high in sugar causes glycation- sugar binds to collagen and elastin and disrupts normal production It’s all about the fibers when it comes to elasticity. Watch Amazing Medical Stories

Fingerprints Loop (60-65%) Whorl (35%) Arch (5%)

The skin as a barrier Is the epidermis waterproof? Is the skin a barrier to all organic molecules? Is lotion water based or lipid based?

Application to pharmacology Nicoderm- cessation of smoking Scopolamine- motion sickness Opiads- pain relief Hormones- including birth control MIT develops new technology that allows larger molecules to pass through the skin. Click on pic to watch movie

Protective barrier Relate the function of apple skin to human skin.

hair shaft sweat gland pore epidermis Basement membrane

Integumentary System Structures Function Skin (cutaneous membrane) Epidermis -stratified squamous epithelial (keratinized)     -stem cells -melanocytes Retards water loss (osmoregulation) Protection from microorganisms Protection from injury Readily divide to replace injured or worm out cells Contain the light absorbing pigment, melanin, which protects deeper cells

The “horny” layer Site of shedding cells An optional layer of dead cells Occurs in areas of heavy wear Layer of dead cells May be absent in areas of thin skin Pre-keratin granules present Cells are alive As few as 2 layers thick in thin skin Cells have spines and are tightly packed One layer thick Site of mitosis

Cellular extension of melanocyte Word Bank Basement membrane Cellular extension of melanocyte Epidermis Golgi apparatus Nucleus Pigment granules 6 1 5 4 3 2