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Chapter 6 Integumentary System - Part 2 (Accessory Structures, Glands, Temperature Regulation, Wounds, Burns)

Accessory Structures of the Skin

  • Originate from the epidermis and extend into the dermis or hypodermis
  • Include: hair follicles, nails, skin glands (sweat and sebaceous)
  • If accessory structures remain intact, injured/burned dermis can regenerate

Nails

  • Protective coverings on the ends of fingers and toes
  • 3 parts of a nail: 3 parts: Nail plate (body), Nail bed, Nail matrix
  • Nail plate: visible portion, keratinized cells, overlies nail bed
  • Nail bed: surface of skin, under nail plate
  • Nail matrix: active growth region, not visible, at proximal end of nail bed
  • Lunula: pale, half-moon-shaped region that lies over nail matrix; nail matrix conceals deeper blood vessels
  • Cuticle: fold at proximal end of nail; part of stratum corneum that extends slightly over nail

Hair Follicles

  • Hair is present on all surfaces of skin except palms, soles, lips, nipples, parts of external reproductive organs
  • Hair follicle: tube-like depression of epidermal cells from which hair develops; extends into dermis or the subcutaneous layer
  • Parts: Hair root, Hair bulb, Hair shaft
  • Hair root: extends from skin surface to dermis or hypodermis
  • Hair bulb: deepest part of hair root; contains dividing cells of hair matrix
  • Hair shaft: portion of hair that extend beyond skin surface; composed of dead epidermal cells
  • Hair papilla contains blood vessels to nourish hair
  • Hair color is due to type and amount of melanin
  • Arrector pili muscle: attached to hair follicle; contracts in response to cold or fear, and causes goosebumps

Hair Loss (Clinical Application 6.2)

  • Pattern baldness (androgenic alopecia): top of head loses hair
  • Associated with lowered level of testosterone (men) or estrogen (women)
  • Progenitor cells are lacking in bald spots, but stem cells are present
  • Alopecia areata: body produces antibodies that attack hair follicles; autoimmune hair loss

Skin Glands: Sebaceous Glands

  • Holocrine glands; usually associated with hair follicles
  • Produce sebum, which consists of fatty material and cellular debris
  • Sebum keeps hair and skin soft and waterproof
  • Excess sebum can result in acne
  • Absent on palms and soles

Acne (Clinical Application 6.3)

  • Acne vulgaris is a disorder of sebaceous glands
  • Common at puberty, because sebaceous glands are excessively responsive to androgens
  • Sebaceous glands become clogged with extra sebum and epithelial cells
  • Clogged glands provide good environment for anaerobic bacteria; infection results in inflammation
  • Affects 80\% of people between 11 and 30 years of age
  • Treated best with Vitamin A derivatives, systemic antibiotics, salicylic acid, benzoyl peroxide

Skin Glands: Sweat Glands

  • Sweat (Sudoriferous) glands: widespread in skin
  • Originate in deeper dermis or hypodermis as ball-shaped coils
  • Types:
    • Eccrine (merocrine) glands: most numerous; consist mainly of water, some salts, wastes; respond to elevated body temperature; open to body surface through pores
    • Apocrine sweat glands: axillary and groin areas; open into hair follicles; secrete by exocytosis; respond to emotions, pain
    • Ceruminous glands: modified sweat glands; secrete ear wax
    • Mammary glands: modified sweat glands; secrete milk

Glands of the Skin (Table 6.2)

  • Sebaceous glands: Keep hair soft, pliable, waterproof; near or connected to hair follicles; not on palms and soles
  • Merocrine (eccrine) sweat glands: Abundant; odorless secretion; lower body temperature; open to surface on forehead, neck, and back
  • Apocrine sweat glands: Less numerous; secretions develop odors; near hair follicles in armpit and groin; wet skin during pain, fear, emotional upset, and sexual arousal
  • Ceruminous glands: Secrete ear wax; External acoustic meatus
  • Mammary glands: Secrete milk; Breasts

Skin Functions

  • Protective barrier: against harmful substances, UV radiation, microorganisms, water loss
  • Sensation: sensory receptors for touch, pressure, temperature changes, pain
  • Excretion of some wastes
  • Production of Vitamin D: starts in skin; activation aids calcium absorption
  • Regulation of body temperature: cools body via sweating and blood flow changes

Heat Production and Loss

  • Important to regulate body temperature; slight shift can disrupt metabolic rates
  • Set point monitored by hypothalamus in brain
  • Deep body temperature stays close to set point of 37^\circ C or 98.6^\circ F
  • Skin plays key role in homeostatic mechanisms that regulate body temperature
  • Heat is product of cellular metabolism; mainly produced by most active cells (liver, skeletal and cardiac muscle)

Heat Loss Through the Skin

  • Methods of heat loss: Radiation (primary), Conduction, Convection, Evaporation

Body Temperature Regulation Mechanisms

  • When body temperature rises:
    • Thermoreceptors signal hypothalamus
    • Vasodilation of dermal blood vessels
    • Vasoconstriction of deep blood vessels
    • Sweat glands are activated
  • When body temperature falls:
    • Thermoreceptors signal hypothalamus
    • Vasoconstriction of dermal blood vessels
    • Vasodilation of deep blood vessels
    • Sweat glands are inactive
    • Muscles contract involuntarily (shivering)

Problems in Temperature Regulation

  • Hyperthermia: abnormally high body temperature
    • Can occur on hot, humid day; sweat cannot evaporate
    • Radiation becomes less effective; body may gain heat from hotter air
    • Skin becomes dry; dizziness, weakness, nausea, headache, rapid pulse
  • Hypothermia: abnormally low body temperature
    • Prolonged exposure to cold or illness
    • Shivering; progression to confusion, lethargy, loss of reflexes, consciousness
    • Without treatment, organs shut down

Elevated Body Temperature (Clinical Application 6.4)

  • Hyperthermia: loss of ability of temperature control mechanism in extremely hot environments
  • If body heat builds up faster than heat can be lost, body temperature rises even if set point is normal
  • Extreme vasodilation can collapse cardiovascular system; may be fatal
  • Fever: set point elevated by immune system to fight infection
  • Phagocytes release pyrogens in response to bacteria/viruses; hypothalamus raises set point; elevated temperature helps destroy pathogens

Healing of Wounds and Burns

  • Inflammation: normal response to injury or stress
  • Blood vessels dilate and become more permeable; fluids leak into damaged tissues
  • Inflamed skin may be reddened, swollen, warm, painful

Cuts

  • Shallow cut (epidermis only): epidermal cells along margin divide rapidly to fill gap
  • Deep cut (reaching dermis/subcutaneous): blood vessels break; clot forms with fibrin, blood cells, platelets; scab forms
  • Epithelial cells reproduce; fibroblasts secrete collagen; growth factors stimulate new tissue
  • Phagocytic cells remove dead cells and debris; scab sloughs off; excess collagen may form a scar

Burns

  • Classified by tissue damage extent:
    • Superficial, partial-thickness (first-degree): injures only epidermis; redness, heat, inflammation; healing in days to weeks; no scarring
    • Deep partial-thickness (second-degree): destroys epidermis and some dermis; may blister; healing varies; stem cells from hair follicles and glands can help regenerate; usually no scarring
    • Full-thickness (third-degree): destroys epidermis, dermis, and accessory structures; prolonged exposure; often requires skin graft or substitutes; limited healing from margins
  • Rule of Nines: divides body surface into regions of 9\% or multiples of 9; used to estimate burn extent for treatment planning (fluids, electrolytes, skin replacement)