Anatomy and Physiology I Unit 5 ReviewThe Integumentary System

Key Structures and Functions

• Integumentary system consists of skin, hair, nails, and exocrine glands
• Skin is the largest organ in the body accounting for 15-20% of total body weight
• Functions include protection, temperature regulation, sensation, excretion, and synthesis of vitamin D
• Skin has two main layers: epidermis (outer layer) and dermis (inner layer)
  • Epidermis is avascular and composed of keratinized stratified squamous epithelium
  • Dermis is vascular and composed of connective tissue
• Subcutaneous layer (hypodermis) lies beneath the dermis and consists of loose connective tissue and adipose tissue
• Accessory structures include hair, nails, and glands (sebaceous, sweat, and ceruminous)

Layers of the Skin

• Epidermis is the outermost layer of the skin
  • Composed of keratinized stratified squamous epithelium
  • Consists of five layers (strata): basale, spinosum, granulosum, lucidum, and corneum
    • Stratum basale is the deepest layer and contains stem cells for regeneration
    • Stratum corneum is the most superficial layer and consists of dead, flattened keratinocytes
• Dermis is the inner layer of the skin
  • Composed of connective tissue (collagen and elastic fibers)
  • Contains blood vessels, nerve endings, hair follicles, and glands
  • Divided into two layers: papillary dermis (superficial) and reticular dermis (deep)
• Subcutaneous layer (hypodermis) lies beneath the dermis
  • Consists of loose connective tissue and adipose tissue
  • Functions include insulation, energy storage, and cushioning

Accessory Structures

• Hair is a keratinized filament that grows from hair follicles in the dermis
  • Consists of a shaft (visible part) and a root (embedded in the follicle)
  • Functions include insulation, protection, and sensory reception
• Nails are keratinized plates that cover the dorsal surface of the distal phalanges
  • Consist of a nail plate, nail bed, and nail matrix (site of nail growth)
  • Functions include protection and enhancing fine motor skills
• Glands are exocrine structures that secrete substances onto the skin surface
  • Sebaceous glands secrete sebum (oily substance) to lubricate and waterproof the skin
  • Sweat glands (eccrine and apocrine) secrete sweat for temperature regulation and excretion
  • Ceruminous glands in the ear canal secrete cerumen (earwax) for protection and lubrication

Protective Mechanisms

• Physical barrier against pathogens, chemicals, and UV radiation
  • Keratinocytes in the epidermis are tightly packed and continuously shed
  • Sebum and sweat create an acidic environment that inhibits bacterial growth
• Immunological defense through skin-associated lymphoid tissue (SALT)
  • Langerhans cells in the epidermis are antigen-presenting cells that activate the immune response
  • Dermal dendritic cells and macrophages in the dermis also contribute to immune defense
• Melanin pigment in the epidermis absorbs and scatters UV radiation
  • Produced by melanocytes in the stratum basale
  • Protects against DNA damage and skin cancer
• Subcutaneous layer provides cushioning and insulation against mechanical injury and heat loss

Homeostatic Roles

• Temperature regulation through vasodilation, vasoconstriction, and sweating
  • Vasodilation increases blood flow to the skin surface for heat dissipation
  • Vasoconstriction reduces blood flow to conserve heat
  • Sweating cools the skin surface through evaporation
• Synthesis of vitamin D in the epidermis upon exposure to UV radiation
  • Vitamin D is essential for calcium absorption and bone health
• Excretion of water, salts, and organic compounds through sweat
  • Helps maintain fluid and electrolyte balance
• Sensation of touch, pressure, temperature, and pain through various receptors in the skin
  • Meissner's corpuscles detect light touch
  • Pacinian corpuscles detect deep pressure and vibration
  • Merkel discs detect sustained pressure
  • Free nerve endings detect temperature and pain

Common Disorders and Diseases

• Acne: inflammation of sebaceous glands and hair follicles
  • Caused by excessive sebum production and bacterial overgrowth
• Atopic dermatitis (eczema): chronic inflammatory skin condition
  • Characterized by dry, itchy, and red skin
• Psoriasis: autoimmune disorder causing rapid keratinocyte proliferation
  • Results in thick, scaly patches on the skin
• Skin cancer: abnormal growth of skin cells
  • Types include basal cell carcinoma, squamous cell carcinoma, and melanoma
  • Often caused by excessive UV exposure
• Pressure ulcers (bed sores): localized damage to the skin and underlying tissue
  • Caused by prolonged pressure, shear forces, or friction
• Burns: tissue damage caused by heat, chemicals, electricity, or radiation
  • Classified by depth (first, second, or third-degree) and extent (percentage of body surface area affected)

Clinical Applications

• Skin grafting: transplantation of healthy skin to cover wounds or burns
  • Types include autografts (from the same individual), allografts (from another individual), and xenografts (from another species)
• Topical medications: drugs applied directly to the skin surface
  • Examples include corticosteroids for inflammation, antibiotics for infections, and retinoids for acne
• Cosmetic procedures: treatments aimed at improving the appearance of the skin
  • Examples include dermabrasion, chemical peels, and laser resurfacing
• Skin biopsies: removal of skin samples for diagnostic purposes
  • Used to evaluate suspicious lesions or diagnose skin conditions
• Mohs surgery: precise surgical technique for removing skin cancers
  • Involves removing thin layers of tissue and examining them microscopically until cancer-free margins are achieved

Key Takeaways and Review

• The integumentary system consists of the skin, hair, nails, and exocrine glands
• Skin has two main layers: epidermis (outer) and dermis (inner), with the subcutaneous layer (hypodermis) beneath
• Accessory structures include hair, nails, and glands (sebaceous, sweat, and ceruminous)
• Skin provides protection, temperature regulation, sensation, excretion, and vitamin D synthesis
• Common disorders include acne, atopic dermatitis, psoriasis, skin cancer, pressure ulcers, and burns
• Clinical applications involve skin grafting, topical medications, cosmetic procedures, skin biopsies, and Mohs surgery
• Understanding the structure and functions of the integumentary system is essential for maintaining skin health and treating various skin conditions