Unit 1.3 Skin

• Primary functions of the skin

  • Barrier
  • Vitamin D synthesis
  • Sensation
  • Thermoregulation
• Layers of the epidermis


  • Stratum corneum (superficial)
  • Stratum lucidum*
  • Stratum granulosum
  • Stratum spinosum
  • Stratum basale
• Layers of the dermis


  • Papillary layer
  • Reticular layer (deep)
• Hypodermis


  Subcutaneous fat, deep to dermis
• Stratum lucidum is found in thick skin only
• the epidermis is made of epithelial tissue
• Keratinocytes


  Most cells in the epidermis, produce keratin (durable protein)
• Keratinocytes


  • Stem cells in stratum basale are mitotically active and make more keratinocytes
• Melanocytes


  Found in stratum basale, synthesize melanin (brown/black pigment), contained in melanosomes
• UV rays from the sun damage DNA


  Melanin "umbrella" protects against UV
• All people have the same number of melanocytes, but there is variability in baseline melanin production (resulting in differences in skin color)
• Melanin production is increased with UV exposure ("tanning")
• Dendritic cells


  Immune cells in the epidermis that are found in stratum spinosum and stratum granulosum
• Tactile cells


  Sensory receptors in stratum basale, receptors for touch, associated sensory neuron carries information toward the CNS
• Life of a keratinocyte


  1. Birth in stratum basale (stem cells divide to make copies that differentiate into keratinocytes)

  2. Cells pushed up through stratum spinosum

  3. Keratinization begins in stratum granulosum (cells die)

  4. Stratum lucidum (only in thick skin)

  5. Stratum corneum (compact layers of dead keratinocytes)

  6. Cells flake off
• Keratinization is a continuous process, the layers are not homogenous
• Thick skin


  Found where form and function require it (e.g. palms, soles)
• Epidermal sublayers in order


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


  • Connective tissue, papillary layer closest to epidermis (loose areolar tissue), reticular layer thicker (dense irregular CT), nutrients from capillaries only reach as far as stratum granulosum
• Thermoregulation


  Involves altering blood flow through cutaneous plexus (in reticular layer)
• Sensory receptors in dermis


  • Tactile
  • Bulbous
  • Lamellar
• Hypodermis


  Subcutaneous tissue, adipose storage (adipose is CT)
• Tattoos reach the dermis of the skin
• Skin issues


  • Stretch marks
  • Blisters
• Types of sweat glands


  • Eccrine (found everywhere, important for thermoregulation and homeostasis)
  • Apocrine (become active at puberty, stinky)
• Sweat glands


  Sweat released from secretory cells via exocytosis, contraction by myoepithelial cells sends sweat out through ducts
• Sebaceous glands


  Produce oil, usually associated with hair follicle, help lubricate and waterproof skin/hair, largest on face, chest, neck, back
• Acne vulgaris is caused by blocked sebaceous gland ducts leading to inflammation
• Vitamin D synthesis


  Initiated in skin, vitamin D precursor 7-dehydrocholesterol (7-DHC) present in skin, photochemically converted by UV, further converted in liver to active form
• Vitamin D is needed for calcium absorption
• • As new cells are produced, older cells above get pushed closer to surface