2.  Protection ◦ Physical barrier against foreign substances ◦ Protects against UV rays ◦ Reduces water loss  Body temperature regulation ◦ Overheating of body  Prevented as capillaries in dermis dilate and bring greater volume of blood to body surface  Body surface becomes wet, cooling by evaporation ◦ Heat conservation  Constriction of dermal capillaries  Excretion ◦ Nitrogenous wastes and salt in sweat  Sensation ◦ Nerve endings, specialized receptors  Vitamin D production ◦ Occurs in presence of sunlight, UV rays ◦ Helps maintain optimum levels of calcium and phosphate

3.  Outermost layer of skin  Develops from embryonic ectoderm  Lacks blood vessels  Skin color is primarily determined by a dark pigment called melanin  But is also influenced by the yellow pigment carotene and by the dermal blood vessels  Generally thin, but can thicken as calluses  In most areas four epidermal layers

5.  Stratum corneum ◦ Outermost layer ◦ Consists of dead, squamous cells filled with keratin ◦ Cells are also coated with lipids, to prevent water loss ◦ Layers of cells increase in areas of friction producing a callus ◦ Over a bony prominence, can thicken and produce a corn  *[Stratum lucidum]* ◦ Consists of about 5 layers of clear, flat, dead cells ◦ Present only in thick skin of palms and soles  Stratum granulosum ◦ Cells contain granules that expand, cell nucleus dies, so outermost cells of this layer are dead ◦ Granules release lipid secretion, prevents water loss and foreign entry  Stratum spinosum ◦ 8-10 layers of cells ◦ Projections of melanocytes appear and Langerhans cells  Stratum germinativum/basale ◦ Deepest layer ◦ Consists of cuboidal or columnar cells that undergo mitotic divisions about every 19 days ◦ As new cells are formed, other cells are pushed toward the surface, journey takes 40-56 days (6-8 weeks) ◦ Contains melanocytes, Langerhans cells, and Merkel cells

8.  Epidermis obtains nourishment by diffusion from capillary beds of dermis

9.  Determined by presence and distribution of melanin  Melanin produced by melanocytes  Differences in skin color are due primarily to the amount of melanin produced by cells and its distribution  Yellowish hue due to presence of carotene in the strata of the epidermis

11.  Lies deep to the stratum germinativum  Second main layer of skin  Well supplied with blood vessels, lymph vessels, nerves, glands, sense organs  Has two distinctly separated layers ◦ Papillary layer  Next to basal layer of stratum germinativum  Contains specialized sensory receptors and capillary loops ◦ Reticular layer  Deep layer consisting of bundles of collagenous fibers, continuous with the deeper hypodermis layer

13.  Not part of skin, but important because it attaches skin to underlying structures  Composed of loose connective tissue

15.  Sweat glands- also called sudoriferous glands; distributed over most of body surface ◦ Eccrine sweat glands  Coiled tubules within dermis  Secrete a watery solution of salt, with traces of urea, sulfates, and phosphates ◦ Apocrine sweat glands  Secrete part of their cell contents, so secretin is more complex that true sweat ◦ Ceruminous glands  Produce “wax” in ears  Modified sweat glands  Sebaceous glands ◦ Empty their secretion (sebum) into hair follicles ◦ Serve to oil skin and hair ◦ Especially active in adolescence ◦ In regions of skin lacking hair, glands empty secretions onto epidermis surface

16.  Covers almost entire body  Its growth is due to mitotic activity of epidermal cells at bottom of hair follicles ◦ Hair follicles  Extend from epidermis into dermis  Composed of two layers (1) inner layer gives rise to hair (2) outer layer of connective tissue develops from dermis  Papillae  At bottom of hair follicles; contain blood capillaries for nourishment and mitosis  Arrector pili muscle  Pulls on follicle; causes hair to “stand up”

18.  Single hair ◦ Consists of root (part with follicle) ◦ Shaft (part above skin surface) ◦ Shaft has a central core (medulla) of loose cornified (horn) cells, cortex of tightly compressed keratinized cells that surround medulla and outside cuticle of hard keratinized cells ◦ Hair color primarily due to melanin

19.  Heavily cornified layers of strata corneum and lucidum  Each nail rests on nail bed of stratum germinativum  Mitosis, which produces nail growth, occurs in thickened matrix under proximal end of nail

20.  Pacinian corpuscles ◦ Nerve endings sensitive to deep pressure  Vitiligo ◦ Partial or complete loss of melanocytes from patches of skin, produce irregular white spots  Cyanotic ◦ Nail beds,skin, mucous membranes appear bluish  Jaundice ◦ Yellow appearance to whites of eyes and to light colored skin; due to build up of bilirubin in blood sign of liver disease  Erythema ◦ Redness of the skin, by engorgement of blood vessels

21.  Langerhans cells ◦ Help body fight off microbes in epidermis  Lunula ◦ Whitish semilunar area near nail root  Meissner corpuscle ◦ Nerve endings sensitive to touch  Freckles ◦ Melanin patches  Albinism ◦ Inherited inability to produce melanin

22.  Gray hair ◦ Decline in synthesis of melanin  White hair ◦ Air bubbles in hair shaft; complete absence of pigments  Dark colored hair ◦ Mostly true melanin (eumelanin)  Blonde and red hair ◦ Contain melanin with iron and sulfur (pheomelanin)

23.  ACNE  WARTS  DERMATITIS AND ECZEMA  PSORIASIS  IMPETIGO  MOLES  HERPES SIMPLEX  HERPES ZOSTER (SHINGLES)  CANCERS  BURNS  HEALING OF CUT SKIN  EFFECTS OF AGING

26.  First degree or superficial partial-thickness ◦ Only epidermis  Second degree or deep partial thickness ◦ Immediate blistering ◦ Epidermis and dermis  Third degree or full- thickness ◦ Epidermis, dermis, accessory structures

28. Second degree  Pain is the indicator between second and third degree  Second degree nerve endings are still intact  Third degree nerve endings have been destroyed