integumentary system

• 3 main layers of the skin

  epidermis, dermis, subcutaneous
• subcutaneous layer AKA


  hypodermis
• skin is like a custard slice


  thin icing is epidermis, thick layer is dermis (custard layer), biscuit base is the subcutaneous layer
• 5 functions of the skin

  • protection
  • excretion
  • regulating body temperature
  • sensation
  • synthesis of vitamin D
• epidermis cells are dead so viruses can't infect, and bacterial growth is inhibited by low pH of the skin
• skin has lots of keratin so is tough and fibrous
• epidermis and dermis of the skin is 1-2 mm thick
• skin is thicker on feet and heels (4mm)
• skin is thinner on the eyelids (0.5mm)
• dermis is dense and has irregular connective tissue, has _ proteins present

  elastic fibres and collagen
• if dermis is stretched too far it can tear and result in

  stretch marks
• lower most layer of the epidermis is called the

  stratum basale
• stratum basale is actively dividing, so receive a lot of nutrients from dermal tissue below
• stratum basale cells migrate upwards, where they will die, due to lack of nutrients and oxygen
• layers of the epidermis

  labels

  A) stratum basale

  B) stratum spinosum

  C) stratum granulosum

  D) stratum lucidum

  E) stratum corneum

  
• the epidermis is stratified squamous epithelial tissue
• cells of the epidermis

  labels

  A) keratinocyte

  B) melanocyte

  C) langerhans cells

  D) merkel cell

  
• keratinocytes produce keratin, in process known as keratinisation
• in stratum granulosum cells 


  start to die
• when cells start to die, they release

  lamellar granules, which contain fat help the skin become waterproof
• in the stratum lucidum and corneum the cells are completely dead
• keratinocytes are held together by cell junctions (desmosomes)
• keratin is important in forming the desmosome cell junctions
• melanocytes make melanin in the skin, allow transfer of melanin to other cells in the epidermis
• Langerhans cells originate in

  bone marrow
• Langerhans cells have immune function
• Langerhans cells phagocytose bacteria/microbes detected in the skin
• Merkel cells are in direct contact with sensory neurons
• majority of skin is thin skin
• thin skin covers all skin except

  palms and soles of the feet
• thin skin lacks 


  stratum lucidum
• what layers are thin in thin skin

  stratum spinosum, corneum
• thin skin doesn't have many sensory receptors
• thick skin has


  hair follicles

  arrector pili muscles

  oil glands
• cells are produced in the stratum basale and migrate upwards
• as cells migrate up the epidermis they synthesis and accumulate keratin
• dermis function 


  anchor epidermis
• dermis is made of

  elastic fibres and collagen
• majority of dermis is the reticular region, bits in contact with dermal papillae (papillary region)
• dermal papillae are made of loose areolar tissue and form interdigitations of the epidermis into the dermis