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Epidermis Cells of the Epidermis 1. Keratinocytes: Produce keratin, from stratum basale, move toward upper layers. * Totally new epidermis every 25-45 days = time from birth to death of keratinocyte!

2. Melanocytes: - Spider-shaped, synthesize melanin pigment, in deepest part of epidermis - Melanosomes = melanin granules that are transferred to keratinocytes. - Accumulate on superficial side of keratinocytes forming a pigment shield that blocks UV light of the sun.

3. Langerhans’ Cells - Arise from bone marrow and migrate to epidermis. - These are macrophages that help activate the immune system (get rid of “intruders”) 4. Merkel Cells (Merkel Disc) - At epidermal-dermal junction. - Spiky hemisphere joined to sensory nerve ending (receptor for touch)

Layers of the Epidermis - Thick Skin = palms, fingertips, soles of feet (5 layers/strata) - Thin skin = thinner strata, stratum lucidum absent…found on rest of body.

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Stratum Basale (Basal Layer or Stratum Germinativum) - Deepest, attached to dermis, single row of cells = youngest keratinocytes. - 10-25% = melanocytes (reach up) - some Merkel cells 2. Stratum Spinosum (Prickly layer) - several layers, spiny-shaped cells, filaments, young keratinocytes.

3. Stratum Granulosum (Granular Layer) - 3-5 cells thick, cells more flattened - keratohyaline and lamellate (water- proofing glycolipid) present - last “living” cells in skin 4. Stratum Lucidum (Clear Layer) - thin translucent band above the stratum granulosum; clear, flat, dead keratinocytes…only in thick skin.

5. Stratum Corneum (Horny Layer) - Most superficial layer - 20-30 cells thick, 3/4 of epidermal thickness. - Keratin and thickened cell membranes protect against abrasion and penetration. - Cell remnants = cornified/horny cells shed off (ex: dandruff) 40 lbs of skin are shed in a lifetime by YOU! Dust mites eat these : )

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Bell Ringer: 9.30.2013 What is the most superficial layer of the epidermis? 2. How many layers make up the thick skin? 3. What two types of cells are located in the basal layer of the epidermis?

Dermis - Strong, flexible connective tissue. Your “hide”; animal hide (leather) Collagen, elastin, & reticular fibers Nerve fibers/sensory receptors, blood & lymph vessels, hair follicles, oil and sweat glands.

2 Layers of Dermis Papillary Layer = areolar ct, collagen and elastin fibers. - “dermal papillae” = upper regions that just into epidermis (fingerprints are formed by these ridges…function = to increase gripping ability!) Genetically unique. - Fingerprints are identifying films of sweat left on anything you touch. - Meissner’s Corpuscles = touch receptors

2. Reticular Layer -80% of thickness of dermis found here. -Dense irregular connective tissue. -Lines of cleavage/tension: Refer to patterns of this layer of ct. Longitudinally in head and limbs. Circular in neck and trunk. - If make incision parallel to these lines = skin gapes less, heals more rapidly than if incision across cleavage lines.

Stretch Marks (“Striae”): From extreme stretching of the skin that tears the dermis.

Blister = separation of the epidermis from the dermal layers by a fluid-filled pocket.

Skin Color Melanin: Polymer of aa’s, Yellow to reddish brown to black. UV protection. Freckles and pigmented moles = local accumulation of melanin. Melanocytes stimulated by sunlight = tan. Melanin absorbs light and dissipates energy as heat.

2. Carotene: - Yellow to orange pigment found in carrots for example. Accumulates in stratum corneum and in fatty tissue of hypodermis. 3. Hemoglobin: - The red color of oxygenated red blood cells in dermal capillaries. Gives Caucasians a more pinkish tone because their skin is more transparent and hemoglobin shows through.

Carotenaemia

But…What about sunless tanning?????? Most effective is DHA (dihydroxyacetone), derived from glycerin. DHA interacts with amino acids in the dead skin cells to produce a brown color change. Safe! Not absorbed into the rest of the body. Does a “fake tan” provide any protection against the sun?

Cyanosis: Poorly oxygenated blood; bluish tint to skin.

Bruise: Blood has escaped from a blood vessel/capillary and clots beneath the skin. AKA: Hematoma

Bell Ringer: 10.2.2012 What three pigments make up the color of skin? Describe the 2 layers of the dermis. What type of tissue composes the dermis?