INTEGUMENTARY SYSTEM

• Integumentary system


  Includes the skin, hair, oil and sweat glands, nails, and sensory receptors
• Skin


  • Covers an area of about 2 square meters (22 square feet) and weighs 4.5-5 kg (10-11 lb), about 16% of total body weight
• Major functions of the integumentary system

  • Protection
  • Sensation
  • Vitamin D production
  • Temperature regulation
  • Excretion
• Epidermis


  Superficial, thinner portion of the skin that prevents water loss and resists abrasion
• Dermis


  Deeper, thicker and dense connective tissue portion responsible for most of the skin's structural strength
• Cells in the epidermis

  • Keratinocytes
  • Melanocytes
  • Langerhans cells
  • Merkel cells
• Layers of the epidermis

  • Stratum basale
  • Stratum spinosum
  • Stratum granulosum
  • Stratum lucidum
  • Stratum corneum
• Stratum basale


  • Deepest layer, contains stem cells that undergo cell division to continually produce keratinocytes
• Stratum spinosum


  • Provides strength and flexibility to the skin
• Stratum granulosum


  • Contains the protein keratin and membrane-enclosed lamellar granules
• Stratum lucidum


  • Found only in areas of the body with high exposure to friction, contains large amounts of keratin
• Stratum corneum


  • Multiple layers of dead squamous cells filled with keratin, helps protect deeper layers from injury and microbial invasion
• Dermis


  • Composed of dense collagenous connective tissue, contains nerves, hair follicles, smooth muscles, glands, and lymphatic vessels
• Collagen fibers in the dermis run through different directions, creating tension lines or cleavage lines
• Stretch marks are caused by damage to the dermis due to overstretching of the skin
• Dermal papillae


  • Uppermost portion of the dermis, contains blood vessels and sensory receptors
• Reticular region of the dermis


  • Deeper part of the dermis, contains bundles of collagen and elastic fibers, adipose cells, hair follicles, nerves, oil glands, and sweat glands
• Melanin


  Pigment responsible for skin color, ranging from pale yellow to reddish brown to black
• Carotene


  Pigment that produces a yellowish hue, found in foods like squash and carrots
• Conditions that affect skin color

  • Albinism
  • Freckles
  • Moles
  • Vitiligo
• Subcutaneous tissue


  Layer deep to the dermis, consists of areolar connective tissue and adipose tissue, anchors the skin to underlying tissues and organs
• Subcutaneous tissue thickness is used to calculate an individual's risk for lifestyle diseases like diabetes
• Accessory skin structures


  Hair, glands, and nails
• Hair


  • Protects the skin and other structures of the body, produced in cycles with growth and resting stages, color determined by melanin
• Each hair is a thread of fused, dead, keratinized epidermal cells
• Rows and eyelashes


  • Protect the eyes from foreign particles
• Hair in the nostrils


  • Filters insects and foreign particles to protect the tissues of the respiratory system
• Hair production


  1. Hair bulb rests on hair papilla

  2. Blood vessels in papilla supply nourishment

  3. Epithelial cells in hair bulb divide and undergo keratinization

  4. Hair grows longer as cells added to base

  5. Hair root and shaft consist of dead keratinized epithelial cells

  6. During resting stage, growth stops and hair held in follicle

  7. New hair formed and old hair falls out during next growth stage
• Hair color


  Determined by varying amounts and types of melanin
• Hair


  • Thread of fused, dead, keratinized epidermal cells
  • Consists of shaft, root, hair follicle and hair root plexuses
  • Shaft is superficial portion above skin surface
  • Root is portion below skin surface that penetrates dermis and sometimes subcutaneous layer
  • Has hard cortex surrounding softer medulla
  • Cortex covered by cuticle, a single layer of overlapping cells
• Hair follicle


  • Surrounds hair root and composed of epidermal cells
  • Hair root plexuses are nerve endings that surround each hair follicle and are sensitive to touch
• Arrector pili


  • Bundle of smooth muscle cells that extends from upper dermis to side of hair follicle
  • Contracts under stress to pull hair shafts perpendicular to skin surface
• Glands in the skin

  • Sebaceous glands
  • Sweat glands
• Sebaceous glands


  • Lie in dermis and open into hair follicles or directly onto skin
  • Secrete sebum, an oily substance containing lipids and cellular debris
  • Help soften skin, prevent water loss, and lubricate skin and hair
  • Enlarged sebaceous glands can cause blackheads
• Eccrine sweat glands


  • Produce transparent, watery fluid called sweat that contains small amounts of waste products
  • Widespread through body but abundant in palms, soles, forehead and upper torso
• Apocrine sweat glands


  • Limited to axillary and pubic regions
  • Produce thicker sweat often released during emotional stress
  • Secrete non-strong odor that can develop body odor when bacteria degrade substances in sweat
• Nails


  • Plates of tightly packed, hard, dead, keratinized cells of epidermis
  • Help grasp and manipulate small objects, provide protection to fingers and toes, allow scratching
• Nail body


  Externally visible portion of nail
• Nail root


  Covered portion that extends to nail matrix
• Cuticle (eponychium)


  Stratum corneum that extends onto nail body