Integumentary System – Comprehensive Study Notes (McKinley 4e Chapter 6)

I. Overview of Integumentary System

  • Integumentary system includes the skin (integument) and associated structures.
  • Skin forms two distinct regions:
    • Epidermis (superficial, epithelial tissue)
    • Dermis (deeper, connective tissue)
  • Hypodermis (subcutaneous tissue) lies deep to the skin; not considered part of the skin.
    • Mainly adipose tissue; pads/protects; insulates; energy reserve.
    • Anchors skin to underlying structures; thickens with weight gain.
  • Derivatives of the skin (appendages):
    • Cutaneous glands (sweat glands and sebaceous glands)
    • Hair
    • Nails
  • Overall function: protection, sensation, thermoregulation, metabolism, etc. (see detailed sections).

II. Skin (Integument)

  • Two distinct regions:
    • Epidermis: superficial region, epithelial tissue
    • Dermis: deeper region, connective tissue; contains most skin structures
  • Hypodermis (subcutaneous tissue): not part of the integument; composed of areolar and adipose tissue; anchors skin; energy reserve; padding.
  • Derivatives of the skin include:
    • Sweat glands (eccrine and apocrine)
    • Sebaceous (oil) glands
    • Hair and hair follicles
    • Nails
  • Key structural relationships (from McKinley):
    • Hair follicles and associated glands reside in the dermis
    • Nerves and blood vessels are abundant in the dermis
    • Dermal papillae project into the epidermis to increase surface area for nutrient exchange

III. Skin Color

  • Three pigments contribute to skin color:
    • Melanin
    • Carotene
    • Hemoglobin
  • Melanin
    • Produced by melanocytes in the stratum basale
    • Packaged in melanosomes; transferred to keratinocytes
    • Accumulates on the apical side of nuclei to protect DNA from UV radiation; acts as a pigment shield
    • Skin color variation due to melanin amount, not melanocyte number
    • Two forms of melanin:
    • Eumelanin (black to brown)
    • Pheomelanin (yellow to red)
    • Melanin production increases with UV exposure
    • Freckles and pigmented moles are local accumulations of melanin
    • Albinism is a nonfunctional enzyme in melanin production; same number of melanocytes across individuals
  • Carotene
    • Yellow-orange pigment from vegetables (e.g., carrots)
    • Accumulates in stratum corneum and hypodermis; most noticeable on palms and soles
    • Vitamin A precursor; important for vision and epidermal health
  • Hemoglobin
    • Red/pink color from oxygenated blood; vascularization affects skin tone
  • Skin color diagnostics (clinical cues)
    • Cyanosis: blue skin from low oxygenation
    • Erythema: redness from increased blood flow
    • Pallor: pale color from reduced blood flow or anemia
    • Jaundice: yellow cast from liver issues
    • Bruises (hematomas): clotted blood beneath the skin
  • Additional notes:
    • All humans have the same number of melanocytes; variation comes from activity and type of melanin produced.
    • UV exposure is a key environmental factor influencing melanin production.

IV. Derivatives of the Skin

  • Aka appendages; all derived from the epidermis; most located in the dermis
  • Sweat glands (sudoriferous glands)
    • Exocrine glands with a coiled secretory portion in the reticular layer and a duct to the surface
    • Contain myoepithelial cells that contract to force sweat into ducts
    • Two main types:
    • Eccrine (merocrine) sweat glands
    • Apocrine sweat glands
    • Both secrete via merocrine secretion (exocytosis)
  • Sebaceous (oil) glands
    • Found on most skin surfaces except palms and soles
    • Exocrine; holocrine secretion (rupture of secretory cells)
    • Typically associated with hair follicles; relatively inactive until puberty; stimulated by sex hormones
    • Secrete sebum (oily substance) that softens skin/hair, slows water loss, and has antimicrobial properties
  • Hair and hair follicles
    • Pili (hair); grows from hair follicles in the dermis
    • Hair shaft, root, and bulb region; arrector pili muscle can elevate hair (goosebumps)
    • Hair color determined by melanin; hair types include:
    • Lanugo: fetal hair (mostly shed before birth)
    • Vellus: fine, short hair over most of the body
    • Terminal: long, coarse hair in specific regions
    • Functions: protection, light barrier, heat retention, sensory reception
  • Nails
    • Scalelike modifications of the epidermis on the distal dorsal surfaces of fingers and toes
    • Composed of hard keratin
    • Parts: edge, body, root
    • Function: protect tips of digits; assist in grasping

V. Functions of the Integumentary System

  • Major roles:
    • Protection from external environment (mechanical, chemical, biological barriers)
    • Body temperature regulation
    • Cutaneous sensations (temperature, touch, pain)
    • Metabolic functions (synthesis of vitamin D precursor)
    • Blood reservoir (blood can be shunted to core as needed)
    • Excretion (sweat removes small amounts of nitrogenous wastes and salts)
  • Protective barriers (three types):
    • Physical barriers: dead keratinized cells in stratum corneum; lipids create a water-resistant barrier; blocks most water and water-soluble substances; selective permeability allows lipid-soluble substances to penetrate (e.g., solvents, some drugs, plant oils, heavy metal salts)
    • Chemical barriers: acid mantle formed by skin secretions; low pH inhibits bacterial growth; sebum and defensins have antimicrobial properties; melanin protects DNA from UV radiation
    • Biological barriers: dendritic (Langerhans) cells in the epidermis; macrophages in the dermis; patrol for pathogens and activate immune responses
  • Temperature regulation (negative feedback system)
    • Thermoreceptors in skin and hypothalamus detect temperature changes
    • Hypothalamus processes information and sends signals to effectors: sweat glands and dermal blood vessels
    • If body temperature rises: increased sweat production and vasodilation to dissipate heat
    • If body temperature falls: vasoconstriction to conserve heat; reduced sweat production
  • Cutaneous sensations
    • Rich supply of nerve endings and receptors for touch, temperature, and pain
  • Metabolic functions
    • Vitamin D synthesis: UV-B converts 7-dehydrocholesterol in keratinocytes to vitamin D3 (cholecalciferol) which is later activated to calcitriol; vitamin D supports calcium absorption
    • Detoxification and conversion of carcinogens; activation of certain hormones
  • Blood reservoir and excretion
    • Dermal capillaries can hold up to about 5 ext{ extcurrency}
      ho 0 ext{ extcurrency} 5 ext{ extcurrency}
      % of blood volume under certain conditions (note: representation of percent varies in sources; concept is that dermis can store blood)
    • Sweat excretion: urea and salts can be excreted in sweat
  • Skin absorption
    • Skin is selectively permeable; small, nonpolar molecules are readily absorbed; many substances are blocked
    • Transdermal patches illustrate controlled absorption

VI. Homeostatic Imbalances of the Skin

  • Skin cancer (most common cancer; many tumors are benign)
    • Commonly affects head/neck due to sun exposure; fair-skinned individuals at greatest risk
    • Risk factors: overexposure to UV radiation, chronic irritation of skin
    • Three major types:
    • Basal cell carcinoma
      • Originates from keratinocytes of the stratum basale
      • Cells proliferate and invade dermis/hypodermis slowly; rarely metastasize
      • Usually on the face; treated successfully by surgical excision in about 99 ext{ extcurrency} of cases
    • Squamous cell carcinoma
      • Originates from keratinocytes of the stratum spinosum
      • Grows rapidly; can metastasize if not removed
      • Common on scalp, ears, lower lip, and hands; prognosis good with radiation or surgical removal
    • Melanoma
      • Originates from melanocytes, usually in a pre-existing mole
      • Grows aggressively; highly metastatic; resistant to chemotherapy
      • Treated by wide surgical excision plus immunotherapy
      • Early detection is critical; ABCDE rule for suspicious moles:
      • A: Asymmetry — two sides do not match
      • B: Border — irregular, with indentations
      • C: Color — several colors (black, brown, tan, sometimes red or blue)
      • D: Diameter — larger than 6 ext{ mm} (pencil eraser size)
      • E: Evolving — changes in size, shape, or symptoms
  • Burns
    • Tissue damage due to heat, electricity, radiation, or chemicals; immediate threat is dehydration and electrolyte imbalance
    • If untreated, wound infection poses a risk after about 24 hours
    • Depth classifications:
    • First-degree burns (partial-thickness)
      • Epidermal damage only
      • Localized redness, edema, pain
    • Second-degree burns (partial-thickness)
      • Epidermal and upper dermal damage
      • Similar symptoms to first-degree plus blisters
    • Third-degree burns (full-thickness)
      • Entire thickness of skin damaged; color gray-white, cherry red, or black
      • Nerve endings destroyed; usually requires skin grafts
  • Rule of Nines (for burn severity assessment)
    • Used to estimate burn surface area and fluid loss; guides fluid replacement
    • Criteria for critical burns:
    • > 25 ext{ extcurrency} of body has second-degree burns
    • > 10 ext{ extcurrency} of body has third-degree burns
    • Third-degree burns present on face, hands, or feet
  • Miscellaneous notes from clinical views in the course materials (Clinical View references appear throughout the text for deeper case discussions, e.g., UV radiation, melanoma, etc.)

Key Structural and Functional Points to Remember

  • Integument structure: epidermis (keratinized stratified squamous epithelium) and dermis (dense irregular connective tissue; highly vascular)
  • Epidermal layers (from deep to superficial): Stratum basale, Stratum spinosum, Stratum granulosum, Stratum lucidum (only thick skin), Stratum corneum
  • Major cell types in epidermis: keratinocytes, melanocytes, Langerhans (dendritic) cells, Merkel (tactile) cells
  • Epidermal turnover: Basale layer is the site of active mitosis; journey to surface takes 25-45 ext{ days}; keratinization occurs as cells move upward
  • Dermal layers: Papillary layer (areolar tissue; dermal papillae) and Reticular layer (dense irregular connective tissue; hair follicles, glands, nerves, and blood vessels)
  • Skin appendages and their distribution: eccrine and apocrine sweat glands; sebaceous glands; hair follicles; nails; ceruminous and mammary glands (modified apocrine glands)
  • Physiological roles of skin: barrier protection, thermoregulation, sensory input, vitamin D synthesis, excretion, blood reservoir
  • Skin’s response to injury and disease varies with depth and type of insult; early detection (e.g., melanoma) improves outcomes

Notes and references to course materials (McKinley 4e, Chapter 6) are embedded throughout; some slides in the transcript are labeled as omitted or for clinical view only. If you want, I can extract a condensed one-page quick-review sheet or a detailed outline tailored to a specific exam format (e.g., multiple choice, short answer, or essay).