Integumentary System: Skin, Hair, and Nails Ch. 5 Functions of the Skin 1. Protection – the skin prevents the entry of microorganisms, acts as a permeability barrier, and provides protection against abrasion and UV light 2. Sensation – the skin contains sensory receptors for pain, heat, cold, and pressure 3. Vitamin D production – UV light stimulates the production of a precursor molecule in the skin that is modified by the liver and kidneys to make vitamin D 4. Temperature regulation – Through dilation and constriction of blood vessels, the skin controls heat loss; plus, evaporation of sweat cools the body 5. Excretion – Skin glands remove small amounts of waste products Skin - Structures and Accessory Organs Skin Structure Skin composed of two kinds of tissue Outer EPIDERMIS=stratified squamous capable of keratinizing (becoming hard/tough) Underlying DERMIS=dense connective tissue Epidermis and dermis (which is 20x thicker) are firmly connected Burns cause separation = blister EPIDERMIS composed of 5 layers called STRATA DERMIS composed of 2 layers Deep to dermis is the SUBCUTANEOUS TISSUE (HYPODERMIS) which is essentially loose adipose tissue NOT considered part of the skin Serves as shock absorber and insulates deeper tissues Has lots of blood vessels Skin Structure - Actual Picture 1. Epidermis - 5 Strata *****OUTSIDE THE BODY***** E P Corneum I Lucidum D E Granulosum Spinosum R M I Basale S *****DERMIS***** “Californian Ladies Give Superb Backrubs” a. Stratum Corneum Found at surface of thick and thin skin Normally 15-20 layers of keratinized cells Keratinization ccurs in exposed skin surfaces except anterior surfaces of the eye Dead cells within each layer remain tightly interconnected by desmosomes Shed as large sheets rather than single cells Layer is water-resistant but not waterproof Journey from stratum basale to stratum corneum takes about 15-30 days Dead cells remain in stratum corneum for about 2 weeks before being shed or washed away b. Stratum Lucidum This layer occurs ONLY where skin is hairless and extra thick Palms of hands and soles of feet Cells in this layer are clear, flattened, densely packed, and filled with keratin Doomed because NOT able to get adequate nutrients and oxygen c. Stratum Granulosum “Grainy” layer superficial to stratum spinosum 3-5 layers of keratinocytes that have stopped dividing Become more flatter and produce copious amounts of keratin Cells die and dehydrate creating tightly interlocked layer of keratin fibers surrounded by KERATOHYALIN d. Stratum Spinosum STRATUM SPINOSUM layer situated above stratum basale; means “spiny layer” Consists of 8 to 10 layers of cells, mostly KERATINOCYTES (most abundant epithelial cells) bound together by desmosomes Begin to become flatter and increasingly full of keratin Cells in this layer continue to divide e. Stratum Basale STRATUM BASALE is deepest layer of epidermis; also called s. germinativum Lies closest to the DERMIS Contains the ONLY epidermal cells that receive adequate nourishment (diffusion) of nutrients from dermis Cells in this layer constantly undergoing mitosis Millions of new cells produced DAILY 2. Dermis Dermis is strong, stretchy envelope that helps hold body together (result of collagen and elastic fibers) Incisions made parallel to collagen fibers (cleavage lines) will scar less; stretch marks result when the dermis is damaged from overstretching Dense connective tissue making up dermis consists of two major regions: PAPILLARY LAYER is upper dermal region RETICULAR LAYER is the lower dermal region a. Papillary Layer Uneven with fingerlike projections from its superior surface called DERMAL PAPILLAE which indent epidermis above Many dermal papillae contain capillary loops which supply nutrients to epidermis Other dermal papillae house pain receptors (free nerve endings) and touch receptors (Meissner’s corpuscles) Fingerprints On palms of hand and soles of feet, papillae arranged in definite pattern that forms looped and whorled ridges on epidermal surface that increase friction and enhance gripping ability of fingers and feet Ridges of fingertips covered with sweat pores and leave identifying film of sweat called FINGERPRINTS on nearly everything they touch Can you identify – loops, whorls, and arches? b. Reticular Layer RETICULAR LAYER of dermis is deepest skin layer Contains blood vessels, sweat and oil glands, and deep pressure receptors (Pacinian corpuscles) Many phagocytes found in reticular layer Both collagen and elastic fibers found with layer Collagen = toughness of dermis but also attracts and binds water Elastic = skin elasticity during youth Skin Color Melanin is the group of pigments responsible for skin, hair, and eye color; molecules are brown to black, and/or reddish – yellowish Melanin provides protection from UV light It is produced by special cells called MELANOCYTES that are found primarily in stratum basale Large amounts of melanin occur in some regions of the skin, such as freckles, moles, and darker skin areas Skin Color Melanin production is determined by: genetic factors (different races and albinism) exposure to light (increase in melanin = suntan) hormones (pregnancy hormones will darken the nipples and genitalia, face and chest, and midline of abdomen) Besides melanin, carotene and hemoglobin also contribute to skin color: Carotene, like from squash and carrots, can be deposited in stratum corneum; give skin a yellow-orange pigment color Hemoglobin, a red pigment in RBCs that binds oxygen, can give skin a reddish hue when blood flow increases; decrease in blood flow makes you pale 3. Accessory Organs Skin appendages are hair and hair follicles, small muscles, glands, and nails Each originate in the dermis and arises from epidermis to help maintain homeostasis a. Hair HAIR is produced by a root follicle and is a flexible epithelial structure The follicle encloses the HAIR ROOT and HAIR BULB (base of the root) in the dermal layer; it is nourished by blood vessels The HAIR FOLLICLE is an extension of the epidermis (s. basale) and helps with tissue repair The HAIR SHAFT is part projecting from surface of skin or scalp The hair shaft has three layers (cuticle, medulla, and cortex) Hair Growth Hair is produced in cycles: Growth Phase – formed by the epithelial cells of the hair bulb; cells divide and undergo keratinization; hair grows longer – as new cells form at bulb, and dead cells are moved up with the hair shaft Resting Phase – growth stops and hair is held in the follicle; when growth starts again, the old hair falls out Examples: eyelashes (30 days growth, 105 days rest); scalp hairs (3 years growth, 1-2 years rest) Goose bumps Small bands of smooth muscle cells called ARRECTOR PILI connect each side of hair follicle to dermal tissue When these muscles contract (cold, frightened), hair is pulled upright and we call the dimpled skin “goose bumps” Furry animals use these tiny muscles to thicken the fur layer and trap insulating air; also to appear larger and ferocious b. Glands Are all EXOCRINE glands that release their secretions to skin surface via DUCTS Are two groups of cutaneous glands: Sebaceous glands Sweat glands (merocrine and apocrine) Sebaceous Glands These “oil glands” are found all over body except on palms of hands and soles of feet Ducts usually open into hair follicles but some open onto skin surface SEBUM is lubricant that keeps skin soft and moist and prevents hair from becoming brittle Sebaceous glands become very active when male sex hormones produced in > amounts (in both sexes) during adolescence; acne is an infection of these oil glands Sweat Glands: Merocrine glands MEROCRINE sweat glands most numerous and are found all over the body Typically sweat reaches skin via duct opening externally as funnel-shaped pore These glands play important part of body’s heat regulating equipment; as sweat evaporates, carries large amounts of body heat with it SWEAT is a clear secretion that is primarily water plus some salts; is usually acidic (pH 4-6) which inhibits bacterial growth Sweat Glands: Apocrine Glands Apocrine glands largely confined to axillary and genital areas of body Usually > than eccrine glands and their ducts empty into hair follicles Secretions contain water and salts plus fatty acids and proteins; the secretion is “odorless” but bacterial growth may impart musky, unpleasant odor Begin to function at puberty as a result of hormones (androgens) c. Nails NAIL is scale-like modification of epidermis similar to hoof/claw of other animals Nails have a NAIL BODY (visible, attached portion) and ROOT (embedded in the skin; extending from the NAIL MATRIX) The CUTICLE is stratum corneum that extends onto the nail body Stratum basale of epidermis extends beneath nail as the NAIL BED; the nail matrix and bed give rise to new cells – nails grow continuously The LUNULA is white crescent over the thickened nail matrix Skin – A Diagnostic Aid, Disorders, & Aging Color Changes CYANOSIS - occurs when hemoglobin is poorly oxygenated and blood/skin of Caucasians appear BLUE JAUNDICE (yellow cast) - name given abnormal yellow skin tone; usually signifies liver disorder Excess bile pigments, which are yellow, are absorbed into blood and deposited in blood and body tissues; the liver is not working properly as a result of damage or disease like hepatitis ERYTHEMA (redness) - name given reddened skin and may indicate embarrassment, fever, hypertension, inflammation, or allergy Blood Flow Changes PALLOR (blanching) - certain types of emotional stress (fear, anger, & others) cause some people to become PALE Pale skin may also signify anemia, low blood pressure, or impaired blood flow to area Bruises/Black and blue marks-reveal sites where blood has escaped from circulation and clotted in tissue spaces; Such clotted masses called HEMATOMAS Bedsores (decubitus ulcers) develop in people who are bedridden or confined to a wheelchair; weight compresses tissue and reduces blood flow – leads to destruction of hypodermis and skin Nutritional Changes Vitamin A deficiency – skin produces excess keratin and has a sandpaper texture Vitamin C deficiency – easily bruised skin Iron-deficiency anemia – nails lose their normal contour and become flat High levels of lead can be detected in a hair analysis Three Types of Burns BURN is tissue damage and cell death caused by intense heat, electricity, UV radiation, or certain chemicals Burns are classified according to their severity FIRST-DEGREE-only epidermis is damaged Area becomes red and swollen Temporary discomfort but “usually” NOT serious Heal in 2-3 days without any special attention Sunburn is “usually” a first-degree burn SECOND DEGREE-involve injury to epidermis and upper region of dermis Skin red/painful and BLISTERS appear Sufficient numbers of epithelial cells still present, regrowth (regeneration) of epithelium can occur Normally, no permanent scarring results IF infection prevented First- and Second-degree burns referred to as PARTIAL-THICKNESS BURNS THIRD-DEGREE-destroy entire thickness of skin and are called FULL-THICKNESS BURNS Burned areas appear blanched (gray-white) or blackened Nerve endings in area destroyed so burn area NOT painful NO regeneration is possible so skin grafting required to cover underlying exposed tissues Considered CRITICAL if over 25% of body has second-degree burns or if over 10% of body has third-degree burns OR if there are third-degree burns of face, hands, or feet Rule of Nines Burns result in two life-threatening problems Body loses supply of fluids containing proteins and electrolytes as they seep from burned surface This dehydration/loss of electrolytes can lead to shut down of kidneys and CIRCULATORY SHOCK (inadequate circulation of blood due to low blood volume) Volume of fluid loss can be estimated indirectly by determining how much of surface has been burned using the RULE OF NINES Method divides body into 11 areas each accounting for 9 percent of total body surface Additional area surrounding genitals (perineum) = 1 percent Types of Skin Cancers Skin cancer most common cancer in humans BASAL CELL CARCINOMA - least malignant and most common skin cancer Cells of stratum basale, altered so can no longer form keratin, no longer honor boundary between epidermis and dermis Proliferate & invade dermis and subcutaneous tissue Occur most often on face as shiny, dome shaped nodules that later develop central ulcer with “pearly” beaded edge Slow-growing and seldom metastasizes before discovery Cure rate is 99% (surgical removal) SQUAMOUS CELL CARCINOMA - arises from cells of stratum spinosum Lesion is scaly, reddened papule (small, rounded elevation) that gradually forms shallow ulcer with firm, raised border Appears on scalp, ears, dorsum of hands, lower lip Metastasizes rapidly to lymph nodes if not removed Believed to be “sun-induced” but recovery rate good if caught early (surgery/radiation) MALIGNANT MELANOMA - is cancer of melanocytes Accounts for 5% of skin cancers, rate is rising, and CAN be deadly Can begin anywhere there is pigment (some begin at pigmented mole) Usually appear as spreading brown/black patch that metastasizes rapidly to lymph nodes and blood vessels Survival rate is about 50% The ABCDE Rule for Melanomas A (asymmetry) - two sides of pigment spot or mole do NOT match B (border irregularity) - borders of lesion are not smooth but exhibit indentations C (color) - pigmented spot contains areas of different colors (blacks, browns, tans, and sometimes blue and reds) D (diameter) - spot is larger than 6 mm in diameter (size of pencil eraser) E (evolution) – change or growth of a mole Aging and the Skin Skin is more easily damaged because the epidermis thins and collagen decreases Decrease is elastic fibers in dermis and loss of fat in hypodermis cause skin to sag and wrinkle Decreased activity of sweat glands and decrease in blood supply to dermis result in poor ability to regulate body temperature Decreased activity of sebaceous glands cause skin to become drier Amount of melanocytes increases in some areas to cause age spots Amount of melanin in hair can decrease (gray hair is a mixture of faded hair and white hair – w/ no melanin) Good times!