Integumentary system

• Skin has three layers: epidermis, dermis, subcutaneous tissue
• It consists of skin (epidermis), hair, nails, glands, and blood vessels.
• The integumentary system is the largest organ system, covering about 2 square meters.
• The integumentary system is the largest organ system in the body.
• Dermis is the middle layer of skin that contains blood vessels, nerves, hair follicles, sweat glands, and oil glands.
• Epidermis is the outermost layer of skin that protects against physical damage.
• Functions include protection from physical injury, temperature regulation, sensory perception, excretion of waste products, synthesis of vitamin D, and immune defense against pathogens.
• Epidermal cells are constantly being replaced by new ones through mitosis.
• Functions include protection from injury, temperature regulation, sensation, excretion, vitamin D synthesis, and immune defense.
• Integumentary system


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


  • Consists of two main parts: the superficial, thinner epidermis and the deeper, thicker dermis
• Epidermis


  Composed of keratinized stratified squamous epithelium containing keratinocytes, melanocytes, Langerhans cells, and Merkel cells
• Keratinization


  As cells move from the stratum basale to the surface, they accumulate more and more keratin
• Layers of the epidermis

  • Stratum basale
  • Stratum spinosum
  • Stratum granulosum
  • Stratum corneum
• Thick skin (palms and soles)

  • Has an additional layer, the stratum lucidum, between the stratum granulosum and stratum corneum
• Dermis


  • Composed mainly of connective tissue containing collagen and elastic fibers, divided into the papillary layer and reticular layer
• Papillary layer


  Superficial part of the dermis, containing areolar connective tissue, dermal papillae with touch receptors, capillary loops, and sensory neurons
• Reticular layer


  Deeper part of the dermis, composed of dense irregular connective tissue with bundles of collagen and elastic fibers
• Meissner corpuscle


  Type of touch receptor located in the dermal papillae adjacent to the basement membrane and stratum basale of the epidermis
• Accessory structures of the skin

  • Hair
  • Glands
  • Nails
• Hair


  Thread of fused, dead, keratinized epidermal cells consisting of a shaft, root, and bulb (follicle)
• Hair


  • Associated with arrector pili muscles and sebaceous glands that produce sebum
• Sebaceous glands


  Produce sebum, an oily substance that moistens hairs and waterproofs the skin
• Ceruminous glands


  Present in the outer ear canal, secrete a yellowish substance called cerumen or earwax
• Sudoriferous glands


  Secrete salt and water as sweat to help regulate body temperature
• Types of sudoriferous glands

  • Apocrine
  • Eccrine (merocrine)
• Nails


  Hard, dead, keratinized epidermal cells covering the terminal portions of the fingers and toes
• Parts of a nail

  • Nail body
  • Free edge
  • Nail root
  • Lunula
  • Cuticle
  • Nail matrix
• Functions of the skin

  • Body temperature regulation
  • Protection
  • Cutaneous sensations
  • Vitamin D synthesis
  • Excretion and absorption
• During strenuous physical activities

  Dermal blood vessels dilate and sweat secretion increases to prevent overheating
• In response to low temperatures

  Dermal blood vessels constrict to minimize heat loss
• Parts of the nail

  • Nail body
  • Free edge
  • Nail root
  • Lunula
  • Cuticle
  • Nail matrix
• Nail matrix


  The proximal portion of the epithelium deep to the nail root
• Cell division of the matrix cells

  Produces new nails
• Functions of the skin

  • Body temperature regulation
  • Protection
  • Cutaneous sensations
  • Excretion and absorption
  • Synthesis of vitamin D
• Body temperature regulation


  • Skin contributes to homeostatic regulation of body temperature by liberating sweat at its surface and by adjusting the flow of blood in the dermis
• Protection


  • Keratin in the skin protects underlying tissues from microbes, abrasion, heat, and chemicals
  • Lipids released by lamellar granules inhibit evaporation of water from the skin surface
• During strenuous physical activities

  Dermal blood vessels dilate and sweat secretion increases
• Cutaneous sensations


  • Tactile sensations (touch, pressure, vibration, and tickling)
  • Thermal sensations (warmth and coolness)
  • Pain
• Excretion and absorption


  The skin has a small ability to absorb and excrete chemicals and toxins