Intergumantary

• Integumentary system


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

  The largest organ of the body in surface area and weight, covers the external surface of the body
• Skin

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


  The superficial, thinner portion of the skin composed of epithelial tissue
• Dermis


  The deeper, thicker portion of the skin made of dense irregular connective tissue
• Subcutaneous (hypodermis)


  Deep to the dermis, but not part of the skin
• Cells in the epidermis

  • Keratinocytes
  • Melanocytes
  • Intraepidermal macrophages (Langerhans cells)
  • Tactile epithelial cells
• Lamellar granules


  Release a lipid-rich secretion that acts as a water-repellent sealant
• Keratinisation


  As cells move from one epidermal layer to the next, they accumulate more and more keratin
• Layers of the epidermis (thin skin)

  • Stratum basale
  • Stratum spinosum
  • Stratum granulosum
  • Stratum corneum
• Layers of the epidermis (thick skin)

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


  • Composed mainly of connective tissue containing collagen and elastic fibres, with dermal papillae, touch receptors, and free nerve endings in the superficial part
• Deeper part of the dermis

  • Consists of dense irregular connective tissue containing bundles of collagen and some coarse elastic fibres, with adipose cells, hair follicles, nerves, oil glands, and sweat glands
• Striae


  Permanent stretch marks visible at the skin surface that form after extreme stretching produces tears in the fibres of the dermis
• Skin pigments


  • Melanin
  • Hemoglobin
  • Carotene
• Accessory structures of the skin

  • Hair
  • Glands
  • Nails
• Hair


  • A thread of fused, dead, keratinised epidermal cells that consists of a shaft, a root, and a follicle
• Hair follicle


  • Composed of two layers of epidermal cells, external and internal root sheaths, surrounded by a connective tissue sheath, with nerve endings and a hair bulb containing a papilla with blood vessels
• Arrector pili


  Bundles of smooth muscle associated with hairs that contract under stress to make the hair stand perpendicularly
• Sebaceous glands


  Secrete an oily substance called sebum that keeps skin from drying out, prevents excessive evaporation of water, keeps the skin soft, and inhibits certain bacteria
• Types of sweat glands

  • Apocrine
  • Eccrine
• Nails


  • Hard, dead, keratinised epidermal cells covering the terminal portions of the fingers and toes, with a nail body, free edge, nail root, lunula, cuticle, and nail matrix
• Functions of the skin

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


  Stratum basale cells move into the wound to reproduce and create new layers
• Deep wound healing


  Fibroblasts lay down collagen and form scar tissue while epithelial cells replace the scab with new epidermal tissue
• Aging changes in the skin

  Decrease in collagen and elastic fibres, decrease in fibroblasts, decrease in gland numbers and production, slowing of hair follicles and melanocytes, slower skin healing
• Most age-related skin changes begin around age 40