Dermatology Skin structure and function PR1

• Skin


  Largest organ (15% of our body)
• Integumentary system


  • Contains nerve receptors (to sense pain, sensation, pressure)
  • Regulates body temperature
  • Contains appendages (hair, sebaceous glands, sweat glands, nails)
  • Helps protect body from infections
• Epidermis


  Outermost thin layer of skin
• Layers of epidermis


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


  Contains blood vessels and nerves
• Hypodermis


  Contains subcutaneous tissues and fat
• Stratum corneum


  • Fibrous protein (sturdy and doesn't rub off easily)
  • Has glycoprotein cement
  • Helps prevent water loss and infection
• Stratum basale


  • Consists of stem cells that continually divide to produce new cells
  • Contains melanocytes that produce melanin
• Hypodermis


  • Helps insulate the body
  • Provides padding
  • Anchors skin to underlying tissues
• Components of hypodermis


  • Adipocytes (fat cells)
  • Fibroblasts
  • Macrophages
• Melanin


  • Pigment produced by melanocytes
  • Helps prevent damage from UV light
• Stratum corneum is the outermost layer of the epidermis and is made up of dead, keratinized cells that secrete natural antibiotics
• As the newest cells in the epidermis push into the stratum corneum, the older dead cells are shed off
• Melanin production increases when the skin is exposed to sunlight
• Vitamin D is an important regulator of calcium and phosphate metabolism and is produced in the skin when exposed to sunlight
• People who live closer to the equator have darker skin because it helps protect them from the stronger UV radiation
• Stratum spinosum


  • Contains Langerhans cells that help with immune defense
• Stratum lucidum


  • Only found in thick skin (palms, soles of feet)
  • 2-3 cell layers thick
• Stratum granulosum


  • 5-8 cell layers thick
  • Begins the process of keratinization
• Keratinocytes in the stratum granulosum produce large amounts of keratin precursor proteins and glycolipids which form the epidermal skin barrier
• Dermis

  Consists of 2 layers: Regulates body temperature
• Papillary Layer

  • Contains fibroblasts that produce collagen
  • Arranged in papillae (finger-like projections)
  • Each papilla contains blood vessels and nerve endings
  • Contains Meissner corpuscle which detects fine touch
  • Contains free nerve endings that detect pain
  • Contains macrophages responsible for fingerprints
• Reticular Layer

  • Thicker than papillary layer
  • Contains fibroblasts and scattered macrophages
• Epidermal cells

  • Keratinocytes
  • Melanocytes
  • Langerhans cells
• Fibroblasts

  Produce collagen
• Pacinian corpuscle

  • Onion-shaped structure
  • Necessary for gripping and sensing deep sensations
  • Alerts us to feel when someone grabs our arm
• Body temperature regulation

  1. Increased body temperature (e.g. exercise)

  2. Blood vessels dilate to allow more blood closer to skin surface

  3. Sweat glands secrete sweat to coat skin surface

  4. Heat lost to environment through evaporation

  5. Decreased body temperature (e.g. cold)

  6. Blood vessels constrict to reduce blood flow to skin
• Skin glands

  • Sebaceous glands
  • Sweat glands
• Hair growth cycle

  • Anagen (growing)
  • Catagen (transitional)
  • Telogen (resting)
• Hair types

  • Fine, short, most in body
  • Thick, colored, on scalp, face, limbs
• Anagen


  Active growth phase of the hair follicle, during which the hair shaft grows longer. Can last 2-7 years.
• Catagen


  Short transitional phase that lasts approximately 10 days, during which the hair follicle shrinks and detaches from the blood supply.
• Telogen


  Resting phase of the hair growth cycle, during which the hair follicle remains dormant for about 3 months. At the end of this phase, the hair falls out and the follicle begins a new anagen phase.
• The skin makes up around 16% of total body weight making it the largest organ in the body
• Integumentary system


  The skin along with its accessory structures like oil and sweat glands
• Functions of the integumentary system

  • Protects the body from infections
  • Helps regulate body temperature
  • Contains nerve receptors that detect pain sensation and pressure
• Layers of the skin

  • Epidermis
  • Dermis
  • Hypodermis
• Epidermis


  • Thin outermost layer of skin
  • Made up of multiple layers of developing coratinocytes
  • Coratinocytes are flat pancake shaped cells filled with keratin protein
• Keratin


  Fibrous protein that allows coratinocytes to protect themselves
• Glycolipids


  Help prevent water from easily seeping into and out of the body