Accessory Structures of Skin Epidermal derivatives Cells sink inward during development to form: hair oil glands sweat glands nails Fig. 5.1

Structure & Fxn. of Hair Shaft -- visible medulla, cortex & cuticle straight hair  X-sec round wavy hair  X-sec oval curly hair  x-sec kidney shaped Root -- below the surface Follicle surrounds root external root sheath internal root sheath base of follicle is bulb blood vessels germinal cell layer 3.Hair (pili) have a number of important characteristics: i.hair is composed of dead, keratinized epidermal cells ii.each hair consists of: a. shaft which projects above the surface of the skin b. root which penetrates into the dermis c. hair follicle which surrounds the root iii. hair grows due to cell division occurring in the matrix of the bulb, located at the base of a hair follicle; there is a growth cycle that includes a growth stage and resting stage v. the color of hair is determined primarily by the amount and type of melanin Result of melanin produced in melanocytes in hair bulb: Dark hair contains true melanin Blond and red hair contain melanin with iron and sulfur Graying hair is result of decline in melanin production White hair has air bubbles in the medullary shaft vi. the primary functions of hair are: prevention of heat loss, protection  decreases sunburn, eyelashes help protect eyes, & touch receptors (hair root plexus) senses light touch Fig. 5.5

Hair Growth Growth cycle = growth stage & resting stage Growth stage lasts 2 - 6 yrs. matrix cells @ base of hair root produce length Resting stage lasts 3 mths. matrix cells inactive & follicle atrophies Old hair falls out as growth stage begins again normal hair loss = 70 - 100 hairs/day

Hair Related Structures Arrector pili muscle smooth muscle in dermis contracts w/ cold or fear. forms goosebumps as hair is pulled vertically Hair root plexus detect hair movement associated with hairs are sebaceous (oil) glands, arrector pili muscles, and hair root plexuses Arrector pili [ = hair, as in depilatory ] Mm originate on the top of the dermis & insert near the base of the follicle to erect the hair. When the Arrector pili M contracts, hair is straightened & is pulled upwards, forming a little bump (“goose bump,” or “chicken flesh,” as the Germans say; the medical word is horripilation or ‘scary hair’). This reaction is mostly a leftover when our ancestors had more hair for insulation & communication; it provides little air-trapping insulation for humans. Fig. 5.5

Glands of the Skin Specialized exocrine glands found in dermis Sebaceous (oil) Sudiferous (sweat) Ceruminous (wax) Mammary (milk) Fig. 5.1

Sebaceous (oil) glands Sebum Comb. of cholesterol, proteins, fats & salts keeps hair & skin soft & pliable inhibits growth of bacteria & fungi (ringworm) Acne bacterial inflammation of glands secretions stimulated by hormones @ puberty Fig. 5.6 4.Sebaceous (oil) glands have several important characteristics: i.they are typically connected to hair follicles ii.they secrete an oily substance called sebum which prevents dehydration of hair and skin, & inhibits growth of certain bacteria Sebaceous glands develop from hair follicles & empty into them; these holocrine glands produce sebum, an oily substance that prevents drying of the skin & hair [ sebum = grease ] & contains lysozymes (bactericide). In a few sensitive regions of the skin, such as on the lips, sebaceous glands may be found independently of hair follicles. Sebaceous glands lubricate the nipple for nursing & the female’s vestibule for coitus. Sebum contains pheromones too. What type of secretion (class of glands) do sebaceous glands exhibit? Holocrine secretion  mature cell dies and becomes secretory product. Secretory portion in the dermis Most open onto hair shafts

Sudoriferous (sweat) glands Eccrine (sweat) glands most areas of skin secretory portion in dermis with duct to surface regulate body temperature H2O, NaCl, urea, uric acid, A.A., glucose, & lactic acid 5.Sudoriferous (sweat) glands produce sweat (perspiration) which helps to cool the body by evaporating, and also eliminates small amounts of wastes; there are two types of sweat glands (see Table 5.3): i.numerous eccrine sweat glands which have an excretory duct that opens at a pore at the surface of the epidermis 1. eccrine sweat glands are coiled tubes that directly empty their product onto the epidermal surface. Eccrine sweat glands excrete mostly water with a little salt & wastes [ about 99% water with a little salt, metabolites, & waste products, such as urea ] and are a powerful cooling adaptation. Evaporation of water from your skin surface cools the blood in the dermal layer, and this cooled blood then circulates to cool the remaining body. Sweat also functions to inhibit bacterial growth—it has lysozymes. ii.apocrine sweat glands which are located mainly in the skin of the axilla, groin, areolae, and bearded facial regions of adult males; their excretory ducts open into hair follicles apocrine sweat glands are larger and are concentrated in the axillary, anal, & inguinal regions, and the areola of the nipple. They usually empty into a hair follicle. Apocrine sweat is more viscous, providing a feast for bacteria. Bacterial wastes from the more viscous apocrine sweat adds to one's body odor, so “you might better communicate with your fellow human beings.” Surprise!: Apocrine sweat glands become active in puberty & are concentrated where there’s pubic hair! Apocrine sweat glands are stimulated during emotional stress & sexual arousal; this secretion is commonly referred to as “cold sweat.” Their secretion contains pheromones. Eccrine glands release sweat via merocrine secretion, and apocrine glands through apocrine secretion (see previous section on epithelial tissue & secretory modes). However, new thoughts and studies have pointed to the idea that these are actually, merocrine glands, too!!! Eccrine glands are for thermoregulation, and apocrine glands are for chemical & visual communication. Fig. 5.6 Apocrine (sweat) glands Armpit & pubic regions Also around areolae & bearded regions of adult males Secretory portion in dermis w/ duct that opens onto hair follicle Secretions more viscous & milky (lipids & protein)

Ceruminous glands 6.Ceruminous glands are modified sweat glands located in the ear canal; they are involved in producing a waxy secretion called cerumen (earwax) Provides a sticky barrier that prevents entry of foreign bodies into the ear canal. Ceruminous Glands produce cerumen (ear wax) in the auditory canal, which functions along with sebum & ear hair to trap intruders from reaching the ear drum & middle ear. [ Ceruminous glands are modified sweat glands ] Fig. 22.10 Modified sweat glands produce waxy secretion in ear canal Cerumin contains secretions of oil & wax glands Helps form barrier for entrance of foreign bodies Impacted cerumen may reduce hearing

Structure of Nails Tightly packed keratinized cells Nail root Fig. 5.7 Each nail consists of: a.free edge b.transparent nail body with a whitish lunula at its base c.nail root embedded in a fold of skin Associated with a nail are: a.hyponychium (located under the free edge) attaches the nail to the fingertip b.eponychium (cuticle) attaches the margin of nail wall to neighboring epidermis c.nail matrix below nail root produces growth in which cell division occurs Cells transformed into tightly packed keratinized cells 1 mm per week iii.The functions of nails include helping to grasp and manipulate objects, providing protection against trauma to the ends of the digits, and scratching various body parts. Tightly packed keratinized cells Nail body visible portion pink due to underlying capillaries free edge appears white Nail root buried under skin layers lunula is white due to thickened stratum basale Eponychium (cuticle) stratum corneum layer

Thin Skin vs. Thick Skin Thick skin only on palms and soles thick epidermis (.6 to 4.5 mm.) with distinct stratum lucidum & thick stratum corneum lacks hair follicles and sebaceous glands ii. thick skin covers the palms, palmar surfaces of digits, and soles

Thin Skin vs. Thick Skin Thin skin covers most of body thin epidermis (.1 to .15 mm.) that lacks stratum lucidum lacks epidermal ridges, has fewer sweat glands & sensory receptors i. thin skin covers all body regions except the palms, palmar surfaces of digits, and soles

Photodamage UVA & UVB light can damage skin Acute overexposure causes sunburn UVA produces oxygen free radicals that damage collagen & elastic fibers  leads to wrinkling DNA damage in epidermal cells can lead to skin cancer UVA: Can pass through window glass. Is not affected by a change in altitude or weather. Is present all day and every day of the year. Penetrates deep into skin layers. Is 5% of the sun's rays. Is 20 times more abundant than UVB rays. Affects long-term skin damage. UVB: Cannot pass through window glass. Causes sunburn. Causes tanning. Helps the body with normal vitamin D production. Varies with the season. It is more intense in the summer than in the winter. Varies with weather conditions. Is more intense at midday than in the morning or late afternoon. Is more intense at high altitudes and near the equator. Is 0.5% of the sun's rays. Is protected against by the sun protection factor (SPF) in sunscreens. Is related to more than 90% of nonmelanoma skin cancer. Is related to cataracts. Sunscreens that say "broad-spectrum" can protect the skin from both UVA and UVB rays. Sunscreens come in lotions, gels, creams, and ointments

Skin Cancer 3 common forms of skin cancer basal cell carcinoma (rarely metastasize) squamous cell carcinoma (may metastasize) malignant melanomas (metastasize rapidly) most common cancer in young women arise from melanocytes ----life threatening key to treatment is early detection watch for changes in symmetry, border, color and size risks factors include-- skin color, sun exposure, family history, age & immunological status 1 million cases diagnosed per year

Epidermal Wound Healing 1. Epidermal wound healing- (e.g. 1st degree abrasion or 2nd degree burn) central portion of wound usually extends deep down to the dermis > whereas the wound edges usually involve only superficial damage to the epidermal cells. epidermal wounds are repaired by enlargement & migration of basal cells contact inhibition, & division of migrating & stationary basal cells. Abrasion or minor burn Basal cells migrate across the wound Contact inhibition w/ other cells stops migration Epidermal growth factor stimulates cell division Full thickness of epidermis results from further cell division

Deep Wound Healing If an injury reaches dermis, healing occurs in 4 phases: inflammatory phase has clot unite wound edges and WBCs arrive from dilated and more permeable blood vessels migratory phase begins the regrowth of epithelial cells and the formation of scar tissue by the fibroblasts proliferative phase is a completion of tissue formation maturation phase sees the scab fall off Deep wound healing- injury extends to tissues deep to the epidermis, the repair process is more complex & scar formation results during inflammatory phase, a blood clot unites the wound edges, epithelial cells migrate across the wound, vasodiation & increased permeability of blood vessels delivers phagocytes, and fibroblasts form migratory phase - epithelial cells beneath the scab bridge the wound, fibroblasts begin to synthesize scar tissue, & damaged b.v.’s begin to grow. in this phase the tissue filling the wound is called granulation tissue proliferative phase - the events of the migratory phase intensify maturation phase - scab sloughs off, epidermis is restored to normal thickness, collagen fibers become more organized, fibroblast begin to disappear, & b.v.’s restored Scar formation remains within the boundaries of the original wound keloid scar extends into previously normal tissue collagen fibers are very dense and fewer blood vessels are present so the tissue is lighter in color 4 phases: Inflammatory Migratory Proliferative Maturation Scar formation Hypertrophic Keloid Which phases have been left out of this illustration?

Burns Types of burns: 1st 2nd 3rd Problems that result shock due to water, plasma & plasma protein loss circulatory & kidney problems from loss of plasma bacterial infection First-degree only epidermis (sunburn) Second-degree burn destroys entire epidermis & part of dermis fluid-filled blisters separate epidermis & dermis epidermal derivatives are not damaged heals without grafting in 3 to 4 weeks & may scar Third-degree or full-thickness destroy epidermis, dermis & epidermal derivatives damaged area is numb due to loss of sensory nerves Destruction of proteins of the skin chemicals, electricity, heat

Skin Grafts New skin can not regenerate if stratum basale and its stem cells are destroyed Skin graft is covering of wound with piece of healthy skin To ensure no tissue rejection occurs transplantations are: Autografts (from self) Isografts (from twin) Autologous skin used transplantation of patients skin grown in culture http://www.nlm.nih.gov/medlineplus/ency/article/002982.htm  for more info. Serial documentation of healing skin grafts following burns in an 18 month old child. Photographer: Gigi William's                        

Pressure Sores Decubitus ulcers Caused by constant deficiency of blood flow to tissue Areas affected is skin over bony prominence in bedridden patients Preventable w/ proper care