Skin

• What are the characteristics of the skin?


  Largest single organ of the body

  
  

  functions: protective physical barrier

  
  

  Sensory , thermoregulatory , metabolic
• What are the skin layers?

  Epidermis , dermis and the hypodermis
• What are the characteristics of the epidermis?


  Stratified squamous keratinized epithelium

  
  

  Layers: stratum basale , stratum spinosum , stratum granulosum , stratum lucidum(only thick skin) , stratum corneum

  
  

  Cells: Keratinocytes , melanocytes , merkel's cells , langherans cells
• What are the two types of skin?


  Thick (hairless , thick keratin layer) , thin (hairy and thin keratin layer)
• What are the characteristics of the stratum basale?


  Single layer of cuboidal or columnar cells on the basal lamina , hemidesmosomes and desmosomes

  
  

  Main function:regenerate the epithelium
• What are the characteristics of the stratum spinosum?


  Layer of the polyhedral cells with central nuclei , numerous cytoplasmic processes or spines

  
  

  microspocially: tonofilaments , lamellar granules , golgi derived structures with lipids and glycolipids

  
  

  Function:mechanical strength
• What are the characteristics of the stratum granulosum?

  3-5 layers of flattened cells , keratohyaline granules:basophilic

  Lamellar granules formation and secretion to intercellular space , impermeable layers around the cells , barrier against water loss , barrier to penetration
• What are the characteristics of the stratum corneum?

  15-20 layers of squamous , keratinized cells filled with keratin fillaments , corneocyte or squames: death flat cell filled with keratin
• What are the characteristics of the melanocytes?

  basal layer and hair follicle (location)

  Bound to basal lamina but not to keratinocytes , neural crest derived cells , long irregular cytoplasmic extensions into basal and spinous layer
• What are characteristics of skin colour?


  produce and secrete the pigment melanin , melanin accumulates into granules (melanosomes) , keratinocytes phagocyte the tips of melanocytes , dark and light skins have same number of melanocytes but dark skin have more melanin production and accumulation

  
  

  UV radiation:increase melanocytes and melanin production?
• What are the characteristics of langherhans cells?


  APC derived from monocytes , mainly localized in spinous layer , bind, process and present antigens to T cells , birbeck granules (long granules with a dense central line)
• What are the characteristics of the merkel cells?

  Sensitive mechanoreceptors , localized in basal layer , abundant in fingertips , joined to keratinocytes by desmosomes , neurosecretory granules , in contact with sensory fibers (merkel disk)
• What are the components of the dermis?


  Layer of connective tissue between epidermis and hypodermis

  Two sublayers: papillary layer(loose connective tissue) , dermal papillae (nutrition and union) , type 1 aand 3 collagen fibers , fibroblast , immune cells

  
  

  Reticular layer: dense irregular connective tissue : type 1 collagen fibers , elastic fibers , fewer cells
• What are the components of the vascular network?

  Two plexuses : subpapillary plexus: between papillary and reticular layer , capillary network

  A deep plexus: between dermis and hypodermis , large blood and lymphatic vessels
• What are the functions of the vascular network?


  Nutirition , thermoregulation:

  cold: decrease blood flow to minimize heat loss

  Hot: increase blood flow to facilitate heat loss
• What are the characteristics of the hypodermis?


  Hypodermis , subcutaneous tissue , loose connective tissue and adipocytes , vessels and nerves
• What are the characteristics of the sensory receptors?

  Unencapsulated receptors: merkel's cells, ferve nerve endings

  
  

  Encapsulated receptors: meissner corpuscles , pacinian corpuscles , krause end bulbs , ruffini corpuscles
• What are the features of the meissner corpuscles?


  Dermal papillae of the hairless skin , modified schwann cell , numerous in fingertips , light touch
• What are the features of the pacinian corpuscles?

  Oval structures in reticular dermis and hypodermis , touch , pressure , vibration
• What are the features of hair follicles?


  keratinized structures formed within epidermal invaginations , hair bulb: terminal dilation , arrector pili muscle : a small bundle of smooth muscle cells , erect the hair when its cold
• What are the features of skin glands?

  Sebaceous glands , embedded in the dermis , acinar glands with a short duct that empties into an hair follicle , pilosebaceous gland , holocrine secretion of sebum protection.

  
  

  Sweat: long epidermal invaginations d=embedded in the dermis , eccrine sweat glands , apocrine sweat glands
• What are the features of eccrine glands?

  Secretory-stratified cuboidal epithelium , clear cells in the basal lamina produce swear , dark cells , myoepithlial cells in the basal lamina contract to help secretion , ducts(two layers)
• What are the features of apocrine glands?

  Secretory- simple cuboidal epithelium , larger lumen

  
  

  Ducts: Usually open into a hair follicle

  
  

  Axillary and perineal regions

  Phermones