LEC: INTEGUMENTARY SYSTEM

• Thick skin:

  • covers the palm and soles
  • dermal papillae are longer
  • contains numerous sweat glans
• Thick Skin size: 400-1400 um
• Thin skin:

  • covers the whole body except the palms and soles
  • its stratum basale is similar to thick skin, but thinner corneum layer and stratum spinosum
  • stratum granulosum and lucidum are not present
• LAYERS OF SKIN:

  • epidermins
  • dermis
  • hypodermis
• Epidermis -consists mainly a stratified squamous keratinized epithelium
• Dermis - connective tissue that supports the epidermis and binds it to the subcutaneous tissue
• Hypodermis - a loose connective tissue that attaches the skin to the underlying tissues
• Epidermis - forms the major distinction between thick skin and thin skin
• Parenchyma - composed of cells in keratinocytes
• 3 epidermal cell types present:

  • melanocytes
  • langerhans cells
  • merkel cells
• Epidermis - composed of stratified squamous epithelium that is capable of keratinizing or becoming hard and tough
• Keratinocytes - produces keratin - waterproofing protein
• Keratinocytes - originate in deeper layers and gets pushed to the surface becomes keratin filled and dies
• keartinocytes are connected to each other by Desmosomes and Tight Junctions
• Cell production and keratinization are accelerated on areas of friction
• callus - thickened skin
• Melanocytes - produce melanin which accumulates on the superficial side of nucleus
• melanocytes - prevents DNA mutation for UV radiation
• UV increase melanin production
• Accumulation in melanin results in freckles and moles
• Melanocytes - comprised of 7-10% of the cells present in the skin
• Melanocytes are bound to basal lamina by hemidesmosomes
• Melanosomes - membrane bound granules where melanin is produces
• Melanocyte - synthesizes melanin granules and transfer them into neighboring keratinocytes of the basal and spinous layers
• Melanocyte - sends irregular dendritic processes between the neighboring keratinocytes for the transfer of the melanin to those cells
• TYPES OF PIGMENT IN THE EPIDERMIS:

  • Eumelanin
  • Pheomelanin
  • Carotene
  • Hemoglobin
• Eumelanin - brown, black pigment
• Pheomelanin - yellow to reddish brown pigment formed from tyr and cyctine
• Carotene - orange yellow pigment from some vegetables
• Carotene - vitamin a precursor
• Vitamin A - forms retinal which is needed for sight
• Hemoglobin - red, oxygen- carrying pigment in erythrocytes
• Langerhans Cells - antigen presenting cells
• Langerhans Cells - present also in other stratified squamous epithelia (oral cavity, esophagus and vagina
• Langerhans Cells - comprise of 3-8% of the cell population present in the epidermis
• Langerhans Cells granules:

  • Birbeck granules
  • Vermiform granules
• Merkel Cells - most numerous in palms and soles
• Merkel Cells are bound to keratinocytes by desmosomes
• Merkel cells - disc shaped cells with short cytoplasmic processes
• Merkel Disc - merkel cell + axon temination