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39 Notes
2012-04-06 12:58:23

Structure, Function, and Disorders of the Integument
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  1. Structure and Function of the Skin
    • Skin is the largest organ of the body and equals 20% of body weight.
    • The skin has two layers – the dermis and epidermis. The hypodermis contains underlying connective tissue, fat cells, fibroblasts, and macrophages.
    • The underlying epidermis contains a basal and spinous layer with melanocytes, Langerhans cells, and Merkel cells.
    • The dermis is composed of connective tissue
    • elements, hair follicles, sweat glands, sebaceous glands, blood vessels, nerves, and lymphatic vessels.
    • The papillary capillaries provide the major blood supply to the skin, arising from deeper arterial plexuses.
    • The derma appendages include nails, hair, and eccrine and apocrine sweat glands.
    • Heat loss and heat conservation are regulated by arteriovenous anastomoses that lead to the papillary capillaries.
    • Pressure ulcers develop from pressure and shearing forces that occlude capillary blood flow with resulting ischemia and necrosis. Areas at greatest risk are pressure points over bony prominences, such as the greater trochanters, sacrum, ischia, and heels.
    • Keloids are sharply elevated scars that extend beyond the border of traumatized skin.
    • Pruritus is itching and is associated with many skin disorders. Small unmyelinated nerve fibers transmit itch sensation.
  2. Disorders of the Skin
    • Contact dermatitis is a form of delayed hypersensitivity that develops with sensitization to allergens, such as metal, chemicals, or poison ivy.
    • Irritant contact dermatitis develops from prolonged exposure to chemicals, such as acids or soaps.
    • Atopic or allergic dermatitis is associated with a family history of allergies, hay fever, elevated IgE levels, and increased histamine sensitivity. Pruritus and scratching predispose the skin to infection, scaling, and thickening.
    • Stasis dermatitis occurs on the legs and results from venous stasis and edema.
    • Stasis dermatitis involves scaly, yellowish, inflammatory plaques of the scalp, eyebrows, eyelids, ear canals, chest, axillae, and back. The cause is unknown but Malassezia yeasts have been implicated.
    • Papulosquamous disorders are characterized by papules, scales, plaques, and erythema.
    • Psoriasis is a chronic inflammatory skin disease associated with T cell activation and thickening of both the epidermis and dermis, characterized by scaly, erythematous, pruritic plaques.
    • Pityriasis rosea is a self-limiting disease characterized by oval lesions with scales around the edges located along skin lines of the trunk and may be caused by a herpes-like virus.
    • Lichen planus is an autoimmune popular, violet-colored inflammatory lesion of unknown origin manifested by severe pruritus.
    • Acne vulgaris is an inflammation of the pilosebaceous follicle.
    • Acne rosacea develops in to he middle third of the face with hypertrophy and inflammation of the sebaceous glands.
    • Lupus erythematosus is an autoimmune disease that can affect only the skin (discoid) or have a systemic presentation. The cutaneous inflammatory lesions usually occur in sun-exposed areas with a butterfly distribution over the nose and cheeks.
    • Pemphigus is a chronic, autoimmune, blistering disease that begins in the mouth or on the scalp and spreads to other parts of the body, often with a fatal outcome.
    • Erythema multiforme is an acute inflammation of the skin and mucous membranes with lesions that appear target-like with alternating rings of edema and inflammation, often associated with allergic reactions to drugs.
    • Folliculitis is a bacterial infection of the hair follicle.
    • A furuncle is an infection of the hair follicle that extends to the surrounding tissue.
    • A carbuncle is a collection of infected hair follicles that forms a draining abscess.
    • Cellulitis is a diffuse infection of the dermis and subcutaneous tissue.
    • Erysipelas is a superficial streptococcal infection of the skin commonly affecting the face, ears, and lower legs.
    • Impetigo may have a bullous or an ulcerative form and is caused by Staphylococcus or Streptococcus.
    • Herpes simplex virus type 1 (HSV-1) causes cold sores but can infect the cornea, mouth, and labia. HSV-2 causes genital lesions and is usually spread by sexual contact.
    • Herpes zoster (shingles) and varicella (chickenpox) are both caused by the same herpesvirus.
    • Warts are benign, rough elevated lesions caused by papollomavirus. Condylomata acuminata, or venereal warts, are spread by sexual contact.
    • Tinea infections (fungal infections) can occur anywhere on the body and are classified by location (i.e., tinea pedis, tinea corporis, tinea capitis).
    • Candidiasis is a yeastlike fungal infection occurring on skin, mucous membranes, and the gastrointestinal tract.
    • Candidiasis is a yeastlike fungal infection occurring on skin, mucous membranes, and the gastrointestinal tract.
    • Urticarial lesions are commonly associated with type 1 hypersensitivity responses and appear as wheals, welts, or hives.
    • Scleroderma is an autoimmune mediated sclerosis of the skin that may also affect systemic organs and cause renal failure, bowel obstruction, or cardiac dysrhythmias.
    • Mosquitoes can transmit infectious diseases, and the saliva from their bite produces the characteristic itching and wheal formation.
    • Blood-sucking flies are represented by many species and their bites are usually painful and produce bleeding, and the itching and local reactions may last for days with systemic symptoms of fever and malaise.
    • Bee sting venom may produce a local or systemic reaction that can be anaphylactic.
    • Seborrheic keratosis is a proliferation of basal cells that produce elevated, smooth, or warty lesions of varying size. They are most common among the elderly population.
    • Keratoacanthoma arises from hair follicles on sun-exposed areas. Three stages of development characterize the lesion, which results in a dome-shaped, crusty lesion filled with keratin that resolves in 3 to 4 months.
    • Actinic keratosis is a pigmented scaly lesion that develops in sun-exposed individuals with fair skin. The lesion may become malignant in the form of a squamous cell carcinoma.
    • Nevi arise from melanocytes and may be pigmented or fleshy pink. They occur singly or in groups and may undergo transition to malignant melanoma.
    • Basal cell carcinoma is the most common skin cancer and occurs most often on sun-exposed areas of the skin.
    • Squamous cell carcinoma is a tumor of the epidermis and can be localized (in situ) or invasive.
    • Malignant melanoma arises from melanocytes, and if not excised early, metastasis occurs through the lymph nodes.
    • Kaposi sarcoma is a vascular malignancy associated with immunodeficiency states and herpes virus-8.
    • Burns are classified according to depth and extent of injury as first, second, or third degree burns.
    • Severe burns cause profound edema and burn shock related to an inflammatory response throughout the cardiovascular system with loss of capillary seal. Fluid resuscitation is critical to prevent shock and death.
    • Burns cause a hypermetabolic response with increased cortisol, glucagon, and insulin levels.
    • Immune suppression associated with inflammatory cytokine release from burned tissue increases risk for infection and can delay wound healing.
    • Frostbite usually occur son cheeks and digits, with direct injury to cells and impaired circulation.
  3. Disorders of the Hair
    • Male-pattern alopecia is an inherited form of irreversible baldness with hair loss in the central scalp and recession of the temporofrontal hairline.
    • Female-pattern alopecia is a thinning of the ventral hair of the scalp beginning in women at 20 to 30 years of age.
    • Alopecia areata is an autoimmune mediated loss of hair and may be associated with stress or metabolic diseases; it is usually reversible.
    • Hirsutism is a male pattern of hair growth in women that may be normal or the result of excessive secretion of androgenic hormones.
  4. Disorders of the Nail
    • Paronychia is an inflammation of the cuticle that can be acute or chronic and is usually caused by staphylococci or streptococci.
    • Onychomycosis is a fungal infection of the nail plate.