Integumentary System

• Integumentary system


  Largest single organ of the body, 15-20% total body weight, made up of skin and its appendages
• Functions of the integumentary system

  • Protection
  • Sensory
  • Thermoregulatory
  • Metabolic
  • Sexual signaling
• Thick skin

  • Located at the palms of the hands and soles of the feet
  • Epidermal layer is 400-1400 um thick

  
• Thin skin


  • Covers the rest of the body
  • Epidermal layer is 75-150 um thick

  
• Epidermal ridges form distinctive patterns unique for each individual, appearing as combinations of loops, arches, and whorls called dermatoglyphs or dermatoglyphics
• Adermatoglyphia


  Rare genetic disorder that prevents the development of fingerprints
• Dermal papilla


  • Contain many blood vessels that supply the overlying epidermis
  • Irregular projections at the junction of the dermis and epidermis
  • Loops located at the dermal layer

  
• Epidermis is avascular, while dermis is rich in blood vessels and nerves
• Layers of the skin

  • Epidermis
  • Dermis
  • Hypodermis

  
• Epidermis


  • Consists mainly of stratified squamous keratinized epithelium
  • Outer layer of the skin

  
• Dermis


  • Connective tissue that supports the epidermis and binds it to the subcutaneous tissue

  
• Hypodermis


  • Loose connective tissue that attaches the skin to the underlying tissues
  • Directly attached to the skeletal muscles
  • Consists of fats

  
• Epidermal cell types

  • Melanocytes
  • Langerhans cells
  • Merkel cells
• Langerhans cells


  Antigen-presenting cells found in the stratum spinosum layer, macrophages in the epidermis
• Merkel cells

  Tactile epithelial cells mostly found in thick skin, located in the granular basal epidermal cells

  
• Layers of the epidermis

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


  Outermost layer, 15-20 layers of flattened, non-nucleated keratinized cells, a barrier to light, heat, chemicals, and microorganisms
• Stratum lucidum


  Only seen in thick skin, a thin, translucent layer of extremely flattened eosinophilic cells

  
• Stratum granulosum

  1. 5 layers of flattened polygonal cells undergoing terminal differentiation, containing keratohyaline granules
• Stratum spinosum

  Polyhedral or slightly flattened cells with central nuclei and nucleoli, actively synthesizing keratin filaments
• Stratum basale


  Basal layer, a single layer of basophilic columnar or cuboidal cells on the basement membrane, intense mitotic activity
• Cells are alive at the bottom of the epidermis and become dead as they move up the layers
• Microneedling treatment pricks and damages the dermal layer, forcing the dermis to produce collagen

  
• Thin skin

  • Epidermis usually shows only four layers
  • Dermis is more cellular and well vascularized than thick skin, with elastin and less coarse bundles of collagen

  
• Melanocyte


  Synthesizes melanin granules and transfers them into neighboring keratinocytes
• Types of melanin

  • Pheomelanin
  • Eumelanin
• Melanin formation

  1. Melanosomes convert amino acid tyrosine into melanin via the enzyme tyrosinase

  2. Melanin forms a cap-like structure in keratinocytes

  3. Melanin absorbs UV radiation
• Dermis


  • Site of epidermal derivatives like hair follicles and glands
  • Rich supply of nerves
• Basement membrane


  Composite structure consisting of the basal lamina and reticular lamina, found between stratum basale and papillary layer of dermis
• Layers of the dermis

  • Papillary layer
  • Reticular layer

  
• Papillary layer


  • Loose connective tissue with fibroblasts, mast cells, and macrophages

  
• Reticular layer

  • Irregular dense connective tissue with a network of elastic fibers, providing elasticity to the skin

  
• Hypodermis


  • Loose connective tissue that binds the skin to underlying organs, allowing the skin to slide over them
  • Contains fat cells that vary in number and size

  
• Sensory receptors in the skin

  • Uncapsulated receptors (tactile disks/Merkel's disks, free nerve endings, root hair plexuses)
  • Encapsulated receptors (tactile corpuscles, Pacinian corpuscles, Ruffini endings, Meissner's corpuscles)
• Loose connective tissue

  • Binds the skin loosely to the subjacent organs, making it possible for the skin to slide over them
  • Contains fat cells that vary in number in different regions of the body and vary in size according to nutritional state (less exercise = more adipocytes = thick hypodermis)

  
• Sensory receptors of the skin

  • Uncapsulated receptors
  • Encapsulated receptors
• Tactile Disks / Merkel's Disks


  Associated with epidermal tactile cells, which function as receptor for light touch
• Tactile


  General term
• Merkel


  Specific term
• Free Nerve Endings


  Respond primarily to high and low temperatures, pain, and itching, but also function as tactile receptors