Integumentary System

• Integumentary System


  • Skin = body's largest and heaviest organ
  • Highly vulnerable to outside forces
  • Receives more medical treatment than any other organ
  • Exposed to radiation, trauma, infection, and chemicals
• Layers of the skin

  • Epidermis
  • Dermis
  • Hypodermis
• Accessories of the Integumentary System

  • Hair
  • Nails
  • Glands – sweat, oil, mammary
• Functions of Skin

  • Resistance to trauma and infection
  • Water (keratin + glycolipids help reduce loss)
  • UV radiation
  • Harmful chemicals
  • Vitamin D synthesis
  • Sensory functions
  • Thermoregulation
  • Non-verbal communication
• Epidermis

  Keratinized stratified squamous epithelium
• Stratum basale


  Deepest layer of epidermis, keratinocytes "born" here from stem cells, high rates of mitosis, tactile (Merkel) cells, melanocytes
• Melanocytes


  Produce melanin (UV absorbing pigment), melanin exported from melanocytes via melanosomes, melanosomes taken in by keratinocytes, melanin granules clustered on superficial side of cell, melanocyte activity genetically & hormonally determined, can be increased by UV exposure
• Melanin & Skin Pigmentation

  Number of melanocytes similar among different skin colors, amount & distribution of melanin produced differs, dark skin – more melanin & more spread out across keratinocytes, light skin – less melanin & concentrated around nucleus of keratinocytes
• Stratum spinosum


  Desmosomes between keratinocytes give "spiny" appearance under microscope, cells also joined by tight junctions – aids in water retention, mitosis in lower layers but ends as you get into upper layers, keratinocytes pushed upward by newly dividing cells in s. basale, dendritic cells "wander" through here
• Stratum granulosum


  Keratohyalin granules in cells, release a protein that binds keratin together creating very tough layer just inside membranes of cells, lamellar bodies release lipid mixture forming epidermal water barrier, cells begin to die
• Stratum lucidum


  Only in thick skin, transparent, flat cells (dead), clear protein – eleidin
• Stratum corneum


  Up to 30 layers of dead keratinocytes, flattened, enucleated, still contain the keratin bundles, what keeps them together if they're dead, eventually flake off – dander
• Dermis


  Connective tissue layer beneath the epidermis, vascular – provides oxygen, nutrients for epidermis, hemoglobin – pink hues, sweat and sebaceous glands, nerve endings, houses hair & nail roots, tattoo ink must reach dermal layer
• Dermis - Cells

  Fibroblasts – produce ECM, mast cells – release chemicals that create inflammatory response (e.g., histamines), leukocytes (white blood cells) – important in immunity
• Dermis – Papillary Layer


  Upper layer, areolar connective tissue, loose organization allows for mobility of leukocytes, extends via dermal papillae into stratum basale of epidermis, creates fingerprints, epidermis has epidermal ridges that reach downward, nerve fibers & touch receptors
• Dermis – Reticular Layer


  Lower layer, dense, irregular connective tissue, itch, stretch & pressure receptors, collagen & elastin fibers provide strength & elasticity, collagen binds to water to keep skin hydrated
• Hypodermis


  Subcutaneous tissue, mostly adipose tissue, some areolar tissue, common site of drug injection (many blood vessels), energy reservoir & thermal insulation