IV. Dermis A. Layer of skin between epidermis and subQ (Hypodermis) layer B. Composed of connective tissue containing collagen and elastic fibers C. Dermal papillae 1. Superficial layer of dermis (top 1/5 of dermis) 2. Papillae (nipple-shaped) structure a). Contains capillary loops – capillaries b). Corpuscles of touch – tactile receptor c). Meissner corpuscles - nerve endings that are sensitive to touch d). Free nerve endings – receive sensations of warmth, coolness, pain, tickling, and itching.

D. The deeper part of the dermis 1. Attached to the subQ (Hypodermis) layer 2. Consists of dense irregular connective tissue containing: a). Collagen, coarse elastic fibers b). Adipose cells, hair follicles, nerves, oil glands, and sweat glands are found in-between the elastic fibers. c). Function of collagen and elastic fibers: i). Extensibility – ability to stretch ii). Elasticity – ability to return to original shape after stretching iii). Striae – Stretch marks (cause by extreme stretching pregnancy and obesity

V. Skin Color A. Three pigments that give color to skin 1. Melanin – Causes skin color: pale yellow, red, tan, and black. a). Melanocytes – cells that produce melanin and transfer it to keratinocytes b). Most plentiful in epidermis of penis, nipples, area around nipples, face, and limbs. c). Number of melanocytes is about the same in all people groups d). Differences in skin color are due to amount of melanin produced by cells. e). Age (liver) spots – Freckle-like blemish; light brown to black in color i. Age spots are areas of skin where melanin accumulate ii. Nevus (Mole) – round, flat, or raised area of overgrown melanocytes -Moles are usually non-cancerous (Benign)

2. Hemoglobin a). Oxygen carrying protein that gives albinos’ skin color range from pink to red. 3. Carotene a). Yellow-orange pigment that fives egg yolk and carrots color. b). Associated with vitamin A (pigments for vision) c). Meals high in carotene can cause the skin to turn orange.

VI. Accessory Structures of the Skin A. Hair 1. Called pili - a thread of fused, dead keratinized cells that consist of a shaft and root 2. Present on most skin surfaces except on palms, fingers, soles, and toes 3. High growth areas are: scalp, eyebrows, and around external genitalia 4. Genetic traits and hormone levels determine thickness and pattern of hair distribution.

5. Structures of the Hair a). Shaft – Superficial portion, which extends above the skin b). Root - Deeper portion, which extends below epidermis and into the dermis c). Hair follicle – Surrounds the root Follicle - a small secretory cavity, sac, or gland d). Hair root plexuses – Nerve endings that are sensitive to touch e). Papilla of the hair – contain blood vessels that provide nourishment f). Matrix – produces new hairs by cell division when old hairs are shed g). Arrector pili – smooth muscle associated with hair i. Extends from the upper dermis to the hair follicle ii. Arrector pili contracts raising hair perpendicular to skin iii. This action causes “goose bumps”

6. Color of Hair a). Melanin is secreted by melanocytes located in the matrix of the hair bulb i. Dark hair contains true melanin ii. Blond and red hair are caused by variants of melanin iii. Gray hair is caused by a decline in melanin production iv. White hair results from trapped air bubbles in the hair shaft

B. Glands of the Skin 1. Sebaceous Glands or oil glands a). Connected to hair follicles b). Oil gland opens into the hair follicle or opens directly on skin’s surface. c). No sebaceous glands on the palms of hands or soles of feet d). Sebum – Oily substance secreted by sebaceous glands i). Keeps hair from drying out ii). Slows evaporation of water from skin iii). Softens skin iv). Inhibits bacterial growth e). Blackheads – blocked sebaceous glands with accumulated sebum i). Sebum is nutritive to certain bacteria causing pimples or boils form ii). The color of blackheads is due to melanin and oxidized oil not dirt

2. Sudoriferous Glands or Sweat Glands a). Three to four million in the skin b). Two kinds i.) Eccrine Sweat Glands -more common than apocrine gland -Most numerous in the skin of forehead, palms, and soles - Gland is deep in dermis and opens by pores in the skin -Glands produce 600mL day (over ½ a liter of sweat) -Sweat contains water, ions, Na +, Cl -, urea, uric acid, ammonia, amino acids, glucose, and lactic acid. -Sweat helps cool the body through evaporation

ii. Apocrine Sweat Glands -Sweat glands located in axilla (armpit), groin, areolae areas, and bearded regions of the face in males. -Glands mostly located in the subQ (hypodermis) layer -Secreted fluid has oils and proteins that make it more viscous -Secreted during emotional stress (cold sweats)

3. Ceruminous Glands a). Located in the skin of external auditory canal of ear b). Cerumen (Earwax) – made up of ceruminous and sebaceous fluid c). Prevents foreign debris from entering the ear canal

C. Nails 1. Made of tightly packed, hard, dead, keratinized cells of the epidermis. 2. Components of nails a). Nail body – visible part of the nail b). Free edge – Part of nail that is clipped – part extends past end of finger or toe c). Nail root – Part of nail not visible, covered by cuticle d). Lunula – whitish crescent next to cuticle e). Nail Matrix – Where the nail grows (1mm per week) f). Cuticle – composed of stratum corneum g). Function – Helps grasp object, protects ends of fingers, allows scratching