Integumentary System Notes
Integumentary System Notes HS 220
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This 8 page Class Notes was uploaded by Annie Estes on Thursday October 13, 2016. The Class Notes belongs to HS 220 at Whitworth University taught by Ulbright in Fall 2016. Since its upload, it has received 6 views. For similar materials see Anatomy and Physiology in Health Sciences at Whitworth University.
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Date Created: 10/13/16
INTEGUMENTARY SYSTEM Introduction and Functions The skin and its accessory structures make up the integumentary system. The integumentary system has several functions: o Protects physical and biochemical integrity: first line of defense from foreign invaders, physical trauma, UV radiation, protects underlying tissues and organs against shock. o Cutaneous sensations: sensory info about the surrounding environment, touch, pressure, pain, temp, tickle, heat, cold. o Body temperature regulation: insulation from cold, evaporative surface for cooling, vasodilation and vasoconstriction to direct blood flow, and prevents H O loss. 2 o Blood reservoir: approximately 8-10% of total blood volume resides in skin, much of which can be shunted to vital organs when necessary. o Helps w/ vitamin D synthesis: activation of a precursor molecule in the skin (7-dehydrocholesterol) by UV light triggers enzymes in the liver and kidneys to produce calcitrol, the most active form of vitamin D. o Storage of nutrients: lipids in adipocytes o Excretion (and some absorption): small roles here – salts, water, some organic wastes, urea, oil o Transdermal drug administration: mediates drug passage across the epidermis and into the blood vessels of the dermis The medical specialty that deals with diagnosing and treating skin disorders is dermatology. Structure of the Skin The skin consists of different tissues that are joined together to perform specific functions and is the largest organ of the body. o Structurally the skin consists of two parts: Epidermis: the superficial portion of the skin, composed of epithelial tissue. Dermis: the deeper layer of the skin, primarily composed of connective tissue. NOTE: Deep to the dermis is the hypodermis (subcutaneous layer). It is not part of the skin. It consists of areolar and adipose tissue (connective tissue). It serves as a fat storage area, an area for blood vessel passage, and an area of pressure nerve endings. NOTE 2: The type of shot someone receives dictates how far the needle will be inserted into a specific layer of the skin. Intracutaneous shot: between epidermis and dermis (e.g. ID injection, local anesthetics, TB & allergy tests. Subcutaneous shot: in the hypodermis (e.g. insulin shot). Intramuscular shot: in skeletal muscle underneath hypodermis (e.g. epi shots). Epidermis o The epidermis is composed of stratified squamous epithelium and contains four principal types of cells: Keratinocytes: produce the protein keratin, which helps protect the skin and underlying tissue from heat, microbes, and chemicals, and lamellar granules, which release a waterproof sealant. Melanocytes: produce the pigment melanin, which contributes to skin color and absorbs damaging UV light. Langerhans cells: participate in immune responses. Merkel cells: contact a sensory structure called a tactile (Merkel) disc and function in the sensation of touch. o There are 4 or 5 layers of the epidermis, depending upon the degree of friction and mechanical pressure applied to the skin. From deepest to most superficial the layers of the epidermis are: Stratum basale (germ layer): the deepest layer of the epidermis, contains some stem cells capable of undergoing cell division to form new cells. When this layer is destroyed (burn, injury), new skin cannot regenerate without a skin graft. Stratum spinosum (spiny layer): provides strength and flexibility to the skin, 8-10 layers, contains keratinocytes and Langerhans cells, desmosomes give strength This layers primary function is defense against microorganisms that manage to penetrate the superficial layers of the epidermis and against superficial skin cancers. Stratum granulosum (grainy layer): transition layer between the deeper, metabolically active cells and the more superficial dead cells, cells in this layer are thinner due to dehydration. Stratum lucidum (clear layer): present only in the fingers, palms, and soles. It’s thick skin, flattened, densely packed, filled with keratin. Stratum corneum: the most superficial layer, consists of dead cells. o Keratinization and growth of the epidermis When deep epidermal cells are pushed up into the superficial epidermal layers, the nucleus and organelles begin to die. Keratinization occurs when dead cell contents are replaced with the protein keratin as cells move to the skin surface over 2-4 weeks. Dermis o The dermis is composed of connective tissue containing collagen and elastic fibers and has two regions: Papillary region: areolar connective tissue containing fine elastic fibers, dermal papillae, sensory receptors (Meissner’s corpuscles), and free nerve endings for sensation of heat, cold, pain, tickle, and itch. Reticular region: deeper part of the dermis consisting of dense, irregular connective tissue containing bundles of collagen fibers and some elastic fibers. Spaces between the fibers may contain adipose cells, hair follicles, sebaceous glands, and sudoriferous glands. The collagen and elastic fibers provide strength, extensibility (ability to stretch), and elasticity (ability to return to original shape after stretching) to skin (sometimes). NOTE: Epidermal ridges (better known as fingerprints) increase friction for better grasping ability and provide the basis for fingerprints and footprints. The ridges typically reflect contours of the underlying dermis. NOTE 2: The cells that make up the dermis are pretty stable. Consequently when someone gets a tattoo, the needle is pushed through the epidermis so the ink can be deposited in the dermis. In doing so, the tattoo is practically permanent. Skin Variations Thin skin (hairy skin): covers all parts of the body except for the palms, palmar surfaces of the digits, and soles. o Thin skin lacks epidermal ridges. o It has a sparser distribution of sensory receptors than thick skin. Thick skin (hairless skin): covers the palms, palmer surfaces of the digits, and soles. o It features a stratum lucidum and thick epidermal ridges. o It lacks hair follicles, arrector pili muscles, and sebaceous glands. o It haas has more sweat glands and sensory receptors than thin skin. Skin color o Skin itself is transparent, the wide variety of colors in skin is due to two main pigments and blood circulation: Melanin (brown, yellow, red, or black): from melanocytes Carotine (orange/yellow tint): from vegetables. Hemoglobin (in blood): blood circulating within the capillaries of the dermis, skin turns red w/ exercise, embarrassment, and burns. o Everyone has melanocytes, it just depends on how much pigment they produce. NOTE: The color of skin and mucuous membranes can provide clues for diagnosing certain problems, such as cyanosis (pale, bluish), jaundice (yellow), and erythema (red). Moles o Small, round, usually dark (black, brown or tan), skin growths densely composed of melanocytes. o May be present at birth or develop during childhood – almost all are present by 40 yrs old. o Very common – the average adult has 40-60 moles on their skin. They may include: Freckles: patches of melanin, sun can increase melanin production. Birthmarks Liver spots: flat tan or brown spots that occur mainly on the face, neck, hands, and forearms. They have nothing to do with the liver. Rather they are the result of sun exposure and aging. Skin tags: small, soft flaps of skin that grow on the neck, in the armpits, and groin area. o Most are not cancerous, but it’s good to check with a physician just in case. Accessory Structures of the Skin Accessory structures of the skin develop from the embryonic epidermis and include hair, glands, and nails. Hair o Hairs, or pili, are present on most skin surfaces except the palms, palmar surfaces of the digits, soles, and plantar surfaces of the digits. o Functions of hair include protection (from UV rays, eye brows), early warning system, decreased heat loss, and light touch sensory. o Anatomy of a hair follicle Shaft: above the surface Root: penetrates the dermis and hypodermis and anchors hair into skin. Bulb: consists of epithelial cells that surround the hair papilla or connective tissue. Cuticle: outer surface of shaft, dead keratinized cells Cortex: intermediate layer, layers of hard keratin, which gives hair its stiffness. Medulla: contains soft keratin which makes hair flexible Other structures associated with hairs are: sebaceous (oil) glands, arrectores pilorum muscles (arrector pili stand hair up, goose bumps), and root plexuses (sensory nerves surround the base of each hair follicle, early warning system or protection). o Hair growth New hairs develop from cell division of the matrix in the bulb. The hair itself is dead and inert. The hair growth cycle consists of a growing stage and a resting stage. Both rate of growth and the replacement cycle can be altered by illness, diet, high fever, surgery, blood loss, severe emotional stress, and gender. Excessive hair loss can result from drugs. o Hair color Hair color is due primarily to the amount and type of melanin and hue of pigment that melanin produces. Can be influenced by hormonal and environmental factors. Graying of hair is due to a progressive decline in tyrosinase, which synthesizes melanin from tyrosine, an inessential AA. White hair results from lack of pigment and presence of air bubbles in medulla. Skin glands o Sebaceous (oil) glands: usually connected to hair follicles, they are absent in the palms and soles Sebaceous glands produce sebum, which moistens hairs, waterproofs and softens the skin, and inhibits bacterial growth. NOTE: Acne results when sebaceous glands become inflamed or colonized by bacteria o Sudoriferous (sweat) glands: divided into two types: Merocrine sweat glands: extensive distribution (approximately 450/square cm in palms), their ducts terminate at pores at the surface of the epidermis. Help regulate body temp through evaporation. Also help eliminate some wastes, such as urea. Apocrine sweat glands: limited distribution, found in skin around axilla, pubis, and areolae, their ducts open into hair follicles. Eliminate sweat during emotional stress or excitement Primarily active after puberty. Ceruminous glands: produce a waxy substance called cerumen (ear wax). These glands are found in the external auditory meatus. Mammary glands: found in the breasts (covered later) Anatomically related to apocrine sweat glands. Combination of sex hormones and pituitary hormones control their development and their secretion. Nails o Nails are hard, keratinized epidermal cells over the dorsal surfaces of the terminal portions of the fingers and toes. o Anatomy of a nail: Body Free edge Root (beneath skin) Lunula: half moon area of white due to increase in basal layer Eponychium: cuticle Hyponychium: epithelium under nail to secure it to the skin Matrix: area of growth o Cell division of the matrix cells produces new cells. o Pinkness of nails is due to blood capillaries beneath cells. o Functionally, nails help in grasping and manipulating small objects in various ways and provide protection against trauma to ends of the digits. Aging and the Integumentary System Vernix caseosa, a fatty secretion from sebaceous glands, covers and protects the skin of the fetus, beginning at about the sixth month of fetal development, and aids in the birth of the fetus. With puberty, some adolescents develop acne. Most effects of aging of the skin do not occur until an individual reaches the late forties. Aging effects of the integumentary system include: o Slower growth of hair and nails, producing thinner finer hairs o Glandular activity declines: skin becomes dry and scaley (sebaceous gland atrophy), merocrine sweat gland activity declines impairing perspiration so elderly are at greater risk of overheating. o Decrease in superficial blood supply: elderly feel cold often o Decrease in number of melanocytes (gray hair, blotching of skin) o Decrease in up to 50% of Langerhans cells (decreased immune responsiveness). o Vitamin D production declines leading to reduced calcium and phosphate absorption eventually leading to muscle weakness and reduced bone strength. o Thinning epidermis and loss of subcutaneous fat, decrease of elastic fiber network, skin becomes weaker, less resilient, sagging, wrinkling. o Decreased ability to heal, reoccurring infections may occur, an injury that takes 2-3 weeks to heal in a young adult may take 6-8 weeks in elderly. Chronic UV exposure causes photodamage to the skin. Maintaining Homeostasis: Skin Wound Healing Epidermal wound healing o In an epidermal wound (e.g. abrasion or a first- or second-degree burn), the central portion of the wound usually extends to the dermis, whereas the wound edges usually involve only superficial damage to the epidermal cells. o Epidermal wounds are repaired by enlargement and migration of basal cells, contact inhibition, and division of migrating and stationary basal cells. o Epidermal Growth Factor stimulates basal cells to divide and replace the ones that have moved into the wound. Deep wound healing o When an injury extends to the dermis or hypodermis, the repair process is more complex than epidermal healing, and scar formation results. o Phases of deep wound healing: Inflammatory phase (preparation): bleeding occurs, mastocytes in the region trigger an inflammatory response, epithelial cells begin to migrate across the wound, vasodilation and increased permeability of blood vessels deliver phagocytes, and fibroblasts form. Migratory phase: after several hours, a (soft) scab begins to form, epithelial cells from the stratum basale beneath the scab bridge the wound, phagocytes remove debris, fibroblasts begin scar tissue, and damaged blood vessels begin to grow. Proliferative phase: up to 1 week, the events of the migratory phase intensify, the scab has been underlined by extensive growth of epithelial cells, fibroblasts randomly deposit collagen, phagocyte activity has almost ended. Maturation phase: >1 week, the scab sloughs off, the epidermis is restored to normal thickness, collagen fibers become more organized, fibroblasts begin to disappear, and blood vessels are restored to normal. o Scar tissue formation (fibrosis) can occur in deep wound healing. Fibrin deposition, no hair, no sensory structures, no glands. Homeostatic Imbalances in the Skin Skin cancer can be caused by excessive exposure to sunlight o Three most common forms: Basal cell carcinoma: malignant stem cells w/in the stratum germinativum. Squamous cell carcinoma: Malignant melanoma: skin cancer originating in malignant melanocytes. o Among the risk factors for skin cancer are skin type, sun exposure, family history, age, and immunologic status. Blisters o A small pocket of fluid that forms between the stratum basale and stratum spinosa, typically caused by acute friction), burning, freezing, chemical exposure or infection. o Most blisters are filled with a clear fluid called serum that leaks in from neighboring tissues as an inflammatory process. Some are filled with blood or pus. o A typical blister forms between the stratum germinativum and stratum spinosa, Calluses o Constant exposure to friction or heat in the stratum corneum layer of the epidermis will cause this layer to increase in depth. The result is formation of a callus. Burns o Tissue damage from excessive heat, electricity, radioactivity, or corrosive chemicals that destroys proteins in the exposed cells. o Depending on the depth of damage, skin burns are classified as: First degree: heals in 3-4 days, only surface of epidermis affected, red, painful due to inflammation of the sun-damaged tissues. Second degree (partial thickness): heals in 3-4 weeks, epidermis and some of the dermis are damaged, blistering, pain, swelling occur, infection possible. Third degree (full thickness): epidermis and dermis and subcutaneous tissues damaged, may be less painful due to sensory nerve damage, damaged accessory structures such as blood vessels hair and glands, infection is likely. Usually can’t heal themselves because granulation tissue cannot form and epithelial cells are unable to cover injury. o The seriousness of a burn is determined by its depth, extent, and area involved, as well as the person’s age and general health. When the burn area exceeds 70% over half of the victims die. Pressure sores o Caused by a constant deficiency of blood to tissues overlying a bony project that has been subjected to prolonged pressure against an object such as a bed, cast, or splint. o The deficiency results in tissue ulceration. Warts o Small rough tumors, often on the hands and feet, that resemble cauliflower or solid blisters. o Typically caused by a viral infection, such as HPV 2 or 7. o Can be contagious, but that is rare. o Treatment includes prescription medication, keratolysis, cryosurgery, surgical excision, laser therapy. Albinism o The inherited inability of an individual to produce melanin or tyrosinase. Vitiligo o The complete or partial loss of melanocytes from patches of the skin resulting in irregular white spots. Psoriasis o A chronic skin disorder characterized by a more rapid division and movement of keratinocytes through the epidermal strata.
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