Chapter 5 The Integumentary System

Transcription

1 Chapter 5 The Integumentary System Copyright 2009, John Wiley & Sons, Inc. 1 Functions of the Skin n regulation of body temperature n blood reservoir n protection n cutaneous sensations n excretion and absorption n synthesis of vitamin D Copyright 2009, John Wiley & Sons, Inc. 2 Components of the Integumentary System Copyright 2009, John Wiley & Sons, Inc. 3 1

2 Introduction n The organs of the integumentary system include the skin and its accessory structures including hair, nails, and glands, as well as blood vessels, muscles and nerves n Who do you go see when you have a skin problem? n Dermatology is the medical specialty for the diagnosis and treatment of disorders of the integumentary system. Copyright 2009, John Wiley & Sons, Inc. 4 Structure of the Skin n The skin (cutaneous membrane) covers the body and is the largest organ of the body by surface area and weight n Its area is about 2 square meters (22 square feet) and weighs 4.5-5kg (10-11 lb), about 16% of body weight q How BIG!!! n It is mm thick, thinnest on the eyelids, thickest on the heels; the average thickness is 1 2 mm Copyright 2009, John Wiley & Sons, Inc. 5 Structure of the Skin n It consists of two major layers: n outer, thinner layer called the epidermis, consists of epithelial tissue n inner, thicker layer called the dermis n Beneath the dermis is a subcutaneous (subq) layer (also called hypodermis) which attaches the skin to the underlying tissues and organs. Copyright 2009, John Wiley & Sons, Inc. 6 2

3 Copyright 2009, John Wiley & Sons, Inc. 7 Copyright 2009, John Wiley & Sons, Inc. 8 Structure of the Skin n The epidermis has a number of important characteristics: n the epidermis is composed of keratinized stratified squamous epithelium n it contains four major types of cells: n Keratinocytes (90% of the cells) produce keratin which is a tough fibrous protein that provides protection Copyright 2009, John Wiley & Sons, Inc. 9 3

4 Types of Cells in the Epidermis Copyright 2009, John Wiley & Sons, Inc. 11 Cell types of the Epidermis n Keratinocytes--90% q produce keratin n Melanocytes % q produces melanin pigment q melanin transferred to other cells with long cell processes n Langerhan cells q from bone marrow q provide immunity n Merkel cells q in deepest layer 5-12 q form touch receptor with sensory neuron Copyright 2009, John Wiley & Sons, Inc. 13 4

5 Types of Skin n There are two major types of skin: n thin (hairy) skin covers all body regions except the palms, palmar surfaces of digits, and soles (4 layers) n thick (hairless) skin covers the palms, palmar surfaces of digits, and soles (5 layers) q stratum lucidum Copyright 2009, John Wiley & Sons, Inc. 14 Epidermis n Keratinization, the accumulation of more and more protective keratin, occurs as cells move from the deepest layer to the surface layer n Dandruff - an excess of keratinized cells shed from the scalp Copyright 2009, John Wiley & Sons, Inc. 15 Epidermis n Stratum basale (deepest layer) or stratum germinativum, where continuous cell division (stem cells) occurs which produces all the other layers n Stratum spinosum, 8-10 layers of keratinocytes n Stratum granulosum, which includes keratohyalin (hard protein envelope) and lamellar granules (release lipids), the most superficial layers die off Copyright 2009, John Wiley & Sons, Inc. 16 5

6 Epidermis n Stratum lucidum is present only in thick skin (the skin of the fingertips, palms, and soles) and is there to protect against usage n Stratum corneum: composed of many layers of flat, dead keratinocytes these are squamous cell shaped, they are continuously shed and replaced by cells from deeper strata; constant friction can stimulate formation of a callus. Copyright 2009, John Wiley & Sons, Inc. 17 Come Let s Get Sun Burnt Copyright 2009, John Wiley & Sons, Inc. 18 Layers of the Epidermis Copyright 2009, John Wiley & Sons, Inc. 19 6

7 Skin Color Pigments (1) n Melanin produced in epidermis by melanocytes q same number of melanocytes in everyone, but differing amounts of pigment produced q results vary from yellow to tan to black color q melanocytes convert tyrosine to melanin n UV in sunlight increases melanin production n Clinical observations q freckles or liver spots = melanocytes in a patch q albinism = inherited lack of tyrosinase; no pigment q vitiligo = autoimmune loss of melanocytes in areas of the skin produces white patches 5-21 Skin Color Pigments (2) n n Carotene in dermis q yellow-orange pigment (precursor of vitamin A) q found in stratum corneum & dermis Hemoglobin q red, oxygen-carrying pigment in blood cells q if other pigments are not present, epidermis is translucent so pinkness will be evident 5-22 Skin Color as Diagnostic Clue n Jaundice q yellowish color to skin and whites of eyes q buildup of yellow bilirubin in blood from liver disease n Cyanotic q bluish color to nail beds and skin q hemoglobin depleted of oxygen looks purple-blue n Erythema q redness of skin due to enlargement of capillaries in dermis q during inflammation, infection, allergy or burns

8 Structural Basis of Skin Color n A benign localized overgrowth of melanocytes is a nevus or mole n Albinism is an inherited inability to produce melanin - vitiligo is a condition in which there is a partial or complete loss of melanocytes from patches of skin Copyright 2009, John Wiley & Sons, Inc. 24 Copyright 2009, John Wiley & Sons, Inc. 25 Structural Basis of Skin Color n Carotene - yellow-orange pigment (found in the stratum corneum, dermis, and subcutaneous layer) n Hemoglobin - red color (located in erythrocytes flowing through dermal capillaries) Copyright 2009, John Wiley & Sons, Inc. 26 8

9 Story Copyright 2009, John Wiley & Sons, Inc. 27 Synthesis of Vitamin D n Sunlight activates a precursor to vitamin D n Enzymes in the liver and kidneys transform that molecule into calcitriol (most active form of vitamin D) n Necessary vitamin for absorption of calcium from food in the gastrointestinal tract 5-28 Photodamage n Ultraviolet light (UVA and UVB) both damage the skin n Acute overexposure causes sunburn n DNA damage in epidermal cells can lead to skin cancer n UVA produces oxygen free radicals that damage collagen and elastic fibers and lead to wrinkling of the skin

10 Copyright 2009, John Wiley & Sons, Inc. 30 Dermis n The dermis has several important characteristics: n is composed of connective tissue containing collagen and elastic fibers n contains two layers n the outer papillary region consists of areolar connective tissue containing thin collagen and elastic fibers, dermal papillae (including capillary loops), corpuscles of touch and free nerve endings Copyright 2009, John Wiley & Sons, Inc. 31 Dermis n The deeper reticular region consists of dense irregular connective tissue containing collagen and elastic fibers adipose cells, hair follicles, nerves, sebaceous (oil) glands, and sudoriferous (sweat) glands n Striae or stretch marks can appear if the skin is stretched too much Copyright 2009, John Wiley & Sons, Inc

11 Dermis n Lines of cleavage - tension lines in the skin indicate the predominant direction of underlying collagen fibers (can be visible if you have stretch marks) n Epidermal ridges reflect contours of the underlying dermal papillae and form the basis for fingerprints (and footprints); their function is to increase firmness of grip by increasing friction. Copyright 2009, John Wiley & Sons, Inc. 33 Subcutaneous Layer n Subcutaneous (subq) layer (also called hypodermis) is not part of the skin but, among its functions, it attaches the skin to the underlying tissues and organs; n this layer (and sometimes the dermis) contains lamellated (pacinian) corpuscles which detect external pressure applied to the skin. Copyright 2009, John Wiley & Sons, Inc. 34 Blood vessels dilate and expand WBC & platelets released from blood vessels Scab forms 11

12 Granulation tissue forms to form a base Epithelial tissue begins regeneration on top of base Clean up begins Scar area has contracted Epithelium regeneration finishes Skin Grafts n New skin can not regenerate if stratum basale and its stem cells are destroyed n Skin graft is covering of wound with piece of healthy skin q autograft from self q isograft from twin q autologous skin n transplantation of patients skin grown in culture

13 Aging and the Integumentary System Effects: wrinkling decrease of skin s immune responsiveness dehydration and cracking of the skin decreased sweat production decreased numbers of functional melanocytes resulting in gray hair and atypical skin pigmentation loss of subcutaneous fat a general decrease in skin thickness an increased susceptibility to pathological conditions n Growth of hair and nails decreases; nails may also become more brittle with age. Copyright 2009, John Wiley & Sons, Inc. 45 Age Related Structural Changes n Collagen fibers decrease in number & stiffen n Elastic fibers become less elastic n Fibroblasts decrease in number n Langerhans cells and macrophages decrease in number and become less-efficient phagocytes n Oil glands shrink and the skin becomes dry n Walls of blood vessels in dermis thicken so decreased nutrient availability leads to thinner skin as subcutaneous fat is lost 5-46 Skin Cancer n 1 million cases diagnosed per year n 3 common forms of skin cancer q basal cell carcinoma (rarely metastasize) q squamous cell carcinoma (may metastasize) q malignant melanomas (metastasize rapidly) n most common cancer in young women n arise from melanocytes ----life threatening n key to treatment is early detection watch for changes in symmetry, border, color and size n risks factors include-- skin color, sun exposure, family history, age and immunological status

14 Malignant melanoma 2% of all cancers Risks: 1. Skin type 2. Sun exposure 3. Family history 4. Age 5. Immunological status Normal mole Melanoma A= asymmetry B= border C= color D= diameter Basal cell carcinoma Easily treated with surgery. (most common skin cancer) Pearly translucent to fleshy color, tiny blood vessels on the surface. Squamous cell Seen as a red, carcinoma (somewhat crusted, or scaly patch common) or bump. Often a very rapid growing tumor. Malignant melanoma (rare, most deadly) The common appearance very asymmetrical and irregular borders 1. In which lay of skin are blood vessels located? 2. Where does epithelium regeneration begin? 3. What color is a persons skin if they are cyanotic? 4. List the layer of the epidermis in order from top to bottom. 5. What is the primary tissue of the hypodermis? 30 14

15 Copyright 2009, John Wiley & Sons, Inc. 51 Excretion and Absorption n Only a minor role is played by the skin n 400 ml of water evaporates from it daily n Small amounts salt, CO2, ammonia and urea are excreted n Lipid soluble substances can be absorbed through the skin q vitamins A, D, E and K, Oxygen and CO2 q acetone and dry-cleaning fluid, lead, mercury, arsenic, poisons in poison ivy and oak 5-53 Burns n Destruction of proteins of the skin q chemicals, electricity, heat n Problems that result q shock due to water, plasma and plasma protein loss q circulatory & kidney problems from loss of plasma q bacterial infection

16 Types of Burns n First-degree q only epidermis (sunburn) n Second-degree burn q destroys entire epidermis & part of dermis q fluid-filled blisters separate epidermis & dermis q epidermal derivatives are not damaged q heals without grafting in 3 to 4 weeks & may scar n Third-degree or full-thickness q destroy epidermis, dermis & epidermal derivatives q damaged area is numb due to loss of sensory nerves 5-55 Copyright 2009, John Wiley & Sons, Inc. 56 Copyright 2009, John Wiley & Sons, Inc

17 Accessory Structures of the Skin n include hair, skin glands, and nails n Hairs (pili) have a number of important functions: q protection q reduction of heat loss q sensing light touch Copyright 2009, John Wiley & Sons, Inc. 58 Accessory Structures of the Skin - Hair n Hair is composed of dead, keratinized epidermal cells n Hair consists of: n shaft which mostly projects above the surface of the skin n root which penetrates into the dermis n hair follicle n epithelial root sheath n dermal root sheath n Sebaceous (oil) glands are connected to hair follicles Copyright 2009, John Wiley & Sons, Inc. 59 Copyright 2009, John Wiley & Sons, Inc

18 Copyright 2009, John Wiley & Sons, Inc. 61 Skin Glands n Sebaceous glands secrete an oily substance called sebum which prevents dehydration of hair and skin, and inhibits growth of certain bacteria n Sudoriferous (sweat) glands-- 2 types: q Eccrine sweat glands q Apocrine sweat glands Copyright 2009, John Wiley & Sons, Inc. 62 Sudoriferous (Sweat) Glands n Numerous eccrine (or merocrine) sweat glands helps to cool the body by evaporating, and also eliminates small amounts of wastes n Apocrine sweat glands, located mainly in the skin of the axilla, groin, areolae, and bearded facial regions of adult males. q their excretory ducts open into hair follicles- this sweat is secreted during emotional stress and sexual excitement. Copyright 2009, John Wiley & Sons, Inc

19 Ceruminous Glands n Modified sweat glands located in the ear canal n Along with nearby sebaceous glands, they are involved in producing a waxy secretion called cerumen (earwax) which provides a sticky barrier that prevents entry of foreign bodies into the ear canal. Copyright 2009, John Wiley & Sons, Inc. 64 Nails n Nails are composed of hard, keratinized epidermal cells located over the dorsal surfaces of the ends of fingers and toes n Each nail consists of: q free edge q transparent nail body (plate) with a whitish lunula at its base q nail root embedded in a fold of skin Copyright 2009, John Wiley & Sons, Inc. 65 Nails Copyright 2009, John Wiley & Sons, Inc

20 Some Diseases and Conditions Copyright 2009, John Wiley & Sons, Inc. 67 Acne vulgaris- common disorder of the sebaceous glands. -Oil is deposited at the opening of the glands. -Oil hardens, clogging openings. -Prevents escape of oil. - White blood cells rush to the area Athlete s foot is a contagious fungal infection. It leads to cracking and scaling. Common in public bathrooms and showers. 20

21 Dermatitisinflammation of the skin caused by various reasons: soap, perfumes, stress, etc. Eczema- not contagious, inflammation of the skin. Dry, red, itchy, and scaly. Usually from allergic reactions to nickel (a common metal found in sterling silver) Psoriasis- chronic inflammatory skin disease with dry red patches covered by silvery-white scales. Affects elbows, knees, shins, scalp, lower back. Cause: unknown. 21

22 Ringwormhighly contagious fungal infection. Raised, itchy, circular patches. (has nothing to do with worms) Hives (urticaria) skin condition that shows intensely itching welts. Usually in response to an allergen. Herpes simplex (type 1)- viral infection around the mouth known as a fever blister or cold sore Genital Herpes simplex (type 2)- viral infection around the genitalia (different from type 1) 22

23 Warts- (Human Papilloma Virus- HPV) Common warts tend to cause no discomfort unless they are in areas of repeated friction or pressure. Warts often go away on their own within two years. Can be treated with chemicals, garlic or freezing methods. Chicken Pox Copyright 2009, John Wiley & Sons, Inc. 77 Shingles (herpes zoster)- viral infection of nerve endings. This is the same virus that causes chicken pox in children. After you get better from chickenpox, the virus "sleeps" (is dormant) in your nerve roots. Usually, it stays dormant forever. In others, the virus "wakes up" when disease, stress, or aging weakens the immune system 23