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Page 653 Chapter 16 Goals Students will be able to: Name the layers of the skin & the accessory structures associated with the skin. Build medical words using the combining forms that are related to the specialty of dermatology Identify lesions, signs & symptoms, & pathologic conditions that relate to the skin Describe laboratory tests & clinical procedures that pertain to the skin, & recognize relevant abbreviations Apply your new knowledge to understanding medical terms in their proper contexts, such as medical reports & records. Skin Chapter 16 Pages 653 – 696 Page 654 Introduction The skin & its accessory structures (hair, nails, & glands) make up the integumentary system of the body. Integument means covering, & the skin (weighing 8 to 10 pounds & extending over an area of 22 square feet in an average adult) is the outer covering for the body. It is, however, more than a simple body covering. This complex system of specialized tissue contains glands that secrete several types of fluids, nerves that carry impulses, & blood vessels that aid in the regulation of the body temperature. Page 654 Introduction: Cont. The skin has many important functions: 1. As a protective membrane over the entire body, the skin guards the deeper tissues of the body against excessive loss of water, salts, & heat against invasion of pathogens & their toxins. 2. The skin contains two types of glands that produce important secretions. These glands in the skin are the sebaceous glands & sweat glands. Sebaceous glands produce sebum, an oily secretion, & sweat glands produce sweat, a watery secretion. Page 654 Introduction: Cont. 3. 4. Nerve fibers under the skin are receptors for sensations such as pain, temperature, pressure, & touch. Nerve fibers coordinate thermoregulation by carrying messages to the skin from heat centers in the brain that are sensitive to increases & decreases in body temperature. Impulses from these fibers cause blood vessels to bring blood to the surface & cause sweat glands to produce the watery secretion that carries heat away. Page 654 Anatomy of the Skin Epidermis = a thin, cellular membrane layer; containing keratin Dermis = dense, fibrous, connective tissue layer; containing collagen Subcutaneous layer = thick, fat-containing tissue Page 654 Anatomy of the Skin: Cont. Epidermis The epidermis is the outermost totally cellular layer of the skin. It is composed of squamous epithelium. Epithelium is the covering of both the internal & the external surfaces of the body. Squamous epithelial cells are flat & scale-like. In the outer layer of the skin, these cells are arranged in several layers (strata) to form stratified squamous epithelium. Page 654 Anatomy of the Skin: Cont. The epidermis lacks blood vessels, lymphatic vessels, & connective tissue & is therefore dependent on the deeper dermis layer & its rich network of capillaries for nourishment. In fact, oxygen & nutrients seep out of the capillaries in the dermis, pass through tissue fluid, & supply nourishment to the lower layers of the epidermis Pages 654 – 655 Anatomy of the Skin: Cont. The deepest layer is called the basal layer. The cells in the basal layer are constantly growing & multiplying & are the source of all the other cells in the epidermis. As the basal layer cells divide, they are pushed upward & away form the blood supply of the dermal layer by a steady stream of younger cells. In their movement toward the most superficial layer of the epidermis, called the stratum corneum, the cells flatten, shrink, lose their nuclei, & die, becoming filled with a hard protein material called keratin. Page 655 Anatomy of the Skin: Cont. The cells are then called keratinocytes, reflecting their composition of keratin. Finally, within 3 to 4 weeks after beginning as a basal cell in the deepest part of the epidermis, the keratinized cell is sloughed off from the surface of the skin. The epidermis is thus constantly renewing itself, with cells dying at the same rate at which they are replaced. This process slows with age. Page 655 Anatomy of the Skin: Cont. The basal layer of the epidermis contains special cells called melanocytes. Melanocytes contain a pigment called melanin that is transferred to the other epidermal cells & gives color to the skin. The number of melanocytes in all human races is the same, but the amount of melanin within each cell accounts for the color differences among the races. Individuals with darker skin process more melanin within the melanocytes, not a greater number of melanocytes. Individuals who are incapable of forming melanin are called albinos. Page 656 Anatomy of the Skin: Cont. Melanin production increases with exposure to strong ultraviolet light, & this creates a suntan, which is a protective response. When the melanin cannot absorb all of the ultraviolet rays, the skin becomes sunburned & inflamed. Over a period of years, excessive exposure to sun tends to cause wrinkles, permanent pigmentary changes, & even cancer of the skin. Because dark-skinned people have more melanin, they acquire fewer wrinkles & they are less likely to develop the types of skin cancer that are associated with ultraviolet light exposure. Page 656 Anatomy of the Skin: Cont. Dermis Dermis = directly below the epidermis; composed of blood vessels, lymph & nerve fibers, as well as the accessory organs of the skin, which are the hair follicles, sweat glands, & sebaceous glands. • To support the elaborate system of nerves, vessels, & glands, the dermis contains connective tissue cells & fibers that account for the extensibility & elasticity of the skin. Page 656 Anatomy of the Skin: Cont. The dermis is composed of interwoven elastin & collagen fibers. Collagen = a fibrous protein material found in bone, cartilage, tendons, & ligaments, as well as in the skin. It is tough & resistant but also flexible. In the infant, collagen is loose & delicate; it becomes harder as the body ages. Collagen fibers support & protect the blood & nerve networks that pass through the dermis. Collagen diseases affect connective tissues of the body. Page 656 Anatomy of the Skin: Cont. Subcutaneous Layer The subcutaneous layer specializes in the formation of fat. Adipocytes are predominant in the subcutaneous layer, & they manufacture & store large quantities of fat. Fat deposition varies in different areas of the body & among individual people. Functionally, this layer of the skin is important in protection of the deeper tissues of the body, as a heat insulator, & for energy storage. Page 656 Accessory Structures of the Skin Hair A hair fiber is composed of a tightly fused meshwork of cells filled with the hard protein called keratin. Hair growth is similar to the growth of the epidermal layer of the skin. Deep-lying cells in the hair root produce keratinized cells that move upward through hair follicles. Melanocytes are located at the root of the hair follicle, & they donate the melanin pigment to the cells of the hair fiber. Of the 5 million hairs on the body, about 100,000 are on the head. They grow about ½ inch per month. Cutting the hair has no effect on its rate of growth. Page 657 Accessory Structures of the Skin: Cont. Nails Nails are hard keratin plates covering the dorsal surface of the last bone of each toe & finger. They are composed of karatinocytes that are cemented together tightly & can extend indefinitely unless cut or broken. A nail grows in thickness & length as a result of division of cells in the region of the nail matrix, which is at the base of the nail plate. Fingernails grow about 1 mm per week, which means that they can regrow in 3 to 5 months. Toenails grow more slowly than fingernails; it takes approximately 12 months for toenails to be replaced completely. Page 657 Accessory Structures of the Skin: Cont. Lunula = a semilunar whitish region at the base of the nail plate. It generally can be seen in the thumbnail of most people & is evident to varying degrees in other fingernails. Air mixed in with keratin & cells rich in nuclei give the lunula its whitish color. Cuticle = a narrow band or epidermis, is at the base & sides of the nail plate. Paronychium nail boarder. = the soft tissue surrounding the Page 657 Accessory Structures of the Skin: Cont. Nail growth & appearacne commonly alter during systemic disease. For example, grooves in nails may occur with high fevers & serious illness, & spoon nails (flattening of the nails plate) develop in iron deficiency anemia. Onycholysis is the loosening of the nail plate with separation for the nail bed. It may occur with infection of the nail & is often seen in psoriasis. Page 658 Accessory Structures of the Skin: Cont. Glands Sebaceous Glands Sebaceous glands are located in the dermal layer of the skin over the entire body, with the exception of the palms, sole, & lips. They secrete an oily substance called sebum. Sebum, containing lipids, lubricates the skin & minimizes water loss. Sebaceous glands are closely associated with hair follicles, & their ducts open into the hair follicle through which the sebum is released. Page 658 Accessory Structures of the Skin: Cont. The sebaceous glands are influenced by sex hormones, which cause them to hypertrophy at puberty & atrophy in old age. Increased production of sebum during puberty contributes to blackhead formation & acne in some people. Page 658 Accessory Structures of the Skin: Cont. Sweat Glands Sweat glands (the most common type are eccrine sweat glands) are tiny, coiled glands found on almost all body surfaces (about 2 million in the body). They are most numerous in the palm of the hand (3,000 glands per square inch) & in the sole of the foot. The coiled eccrine sweat gland originates deep in the dermis & straightens out to extend up through the epidermis. The tiny opening on the surface is a pore. Page 658 Accessory Structures of the Skin: Cont. Sweat, or perspiration, is almost pure water, with dissolved materials such as salt making up less than 1% of the total composition. It is colorless & odorless. The odor produced when sweat accumulates on the skin is caused by the action of bacteria on the sweat. Sweat cools the body as it evaporates into the air. Perspiration is controlled by the sympathetic nervous system, whose nerve fibers are activated by the heart regulatory center in the hypothalamic region of the brain, which stimulates sweating. Page 659 Accessory Structures of the Skin: Cont. A special variety of sweat gland, active only from puberty onward & larger than the ordinary kind, is concentrated in a few areas of the body near the reproductive organs & in the armpits. These glands (apocrine sweat glands) secrete an odorless sweat, containing substances easily broken down by bacteria on the skin. The bacterial waste products produce a characteristic human body order. The milk-producing mammary gland is another type of apocrine gland; it secretes milk after the birth of a child. Page 664 Pathology Cutaneous Lesions crust Collection of dried serum & cellular debris cyst Thick-walled, closed sac or pouch containing fluid or semisolid material erosion Wearing away or loss of epidermis fissure Groove or crack-like sore Flat, pigmented lesion measuring less than macule 1 cm in diameter Page 664 Pathology: Cont. Cutaneous Lesions: Cont. Solid, round or oval elevated lesion 1 cm or nodule more in diameter Small (less than 1 cm in diameter), solid papule elevation of the skin Growth extending from the surface of the polyp mucous membrane pustule Papule containing pus ulcer Open sore on the skin or mucous membrane (deeper than an erosion) Page 664 Pathology: Cont. Cutaneous Lesions: Cont. Small collection (papule) of clear fluid vesicle (serum); blister wheal Smooth, edematous (swollen) papule or plaque that is centrally redder or paler than the surrounding skin. Page 666 Pathology: Cont. Signs & Symptoms alopecia Absence of hair from areas where it normally grows ecchymosis (plural: Bluish-purplish mark (bruise) ecchymoses) on the skin petechia (plural: petechiae) Small, pinpoint hemorrhage pruritus Itching Page 667 Pathology: Cont. Abnormal Conditions Injury to tissue caused by heat contact First-degree burns = superficial epidermal lesions, erythema, hyperesthia, & no blisters Second-degree burns (partial-thickness burns burness burn injury) = epidermal & dermal lesions, erythema, blisters, & hyperesthia Third-degree burns (full-thickness burn injury) = epidermal & dermal are destroyed (necrosis of skin), & subcutaneous layer is damaged, leaving charred, white tissue Pages 666 – 668 Pathology: Cont. Abnormal Conditions: Cont. acne Chronic papular & pustular eruption of the skin with increased production of sebum cellulitis Diffuse, acute infection of the skin marked by local heat, redness, pain, & swelling eczema Inflammatory skin disease with (atopic erythematous, papulovesicular, or dermatitis) papalosquamous lesions. Pages 668 – 670 Pathology: Cont. Abnormal Conditions: Cont. exanthematous Rash (exanthem) of the skin due to viral diseases a viral infection Death of tissue associated with loss gangrene of blood supply Bacterial inflammatory skin impetigo disease characterized by vesicles, pustules, & crusted-over lesions Chronic, recurrent dermatosis psoriasis marked by itchy, scaly, red plaques covered by silvery gray scales Page 670 Pathology: Cont. Abnormal Conditions: Cont. scabies Contagious, parasitic infection of the skin with intense pruritus scleroderma Chronic progressive disease of the skin & internal organs with hardening & shrinking of connective tissue systemic lupus Chronic autoimmune inflammatory erythematosus disease of collagen in skin, joints, (SLE) & internal organs Pages 671 – 672 Pathology: Cont. Abnormal Conditions: Cont. tinea Infection of the skin caused by a fungus urticaria Acute allergic reaction in which red, (hives) round wheals develop on the skin vitiligo Loss of pigment (depigmentation) in area of the skin (milk-white patches). Page 672 Pathology: Cont. Skin Neoplasms Benign Neoplasms Increased growth of cells in the keratin callus layer of the epidermis caused by pressure or friction Excess hypertrophied, thickened scar keloid developing after trauma or surgical incision Thickened & rough lesion of the keratosis epidermis; associated with aging or skin damage Page 673 Pathology: Cont. Skin Neoplasms Benign Neoplasms: Cont. White, thickened patches on mucous leukoplakia membrane tissue of the tongue or cheek nevus (plural: Pigmented lesion of the skin nevi) verruca Epidermal growth (wart) caused by a (plural: virus verrucae) Page 674 Pathology: Cont. Skin Neoplasms Cancerous Lesions basal cell Malignant tumor of the basal cell carcinoma layer of the epidermis squamous cell Malignant tumor of the squamous carcinoma epithelial cells in the epidermis malignant Cancerous growth composed of melanoma melanocytes Malignant, vascular, neoplastic Kaposi growth characterized by cutaneous sarcoma nodules. Page 675 Laboratory Tests & Clinical Procedures Laboratory Tests bacterial analyses Samples of skin are examined for presence of microorganisms fungal tests Scrapings from skin lesions, hair specimens, or nail clippings are sent to a laboratory for culture & microscopic examination Page 675 Laboratory Tests & Clinical Procedures: Cont. Clinical Procedures cryosurgery Use of subfreezing temperature achieved with liquid nitrogen application to destroy tissue curettage Use of a sharp dermal curette to scrape away a skin lesion Tissue is destroyed by burning electrodesiccation with an electric spark Pages 675 – 676 Laboratory Tests & Clinical Procedures: Cont. Clinical Procedures Thin layers of malignant tissue are removed, & each slice is Mohs surgery examined microscopically to check for adequate extent of the resection Suspicious skin lesions are skin biopsy removed or sampled & examined microscopically by a pathologist Substances are injected skin test intradermally or applied to the skin, & results are observed