Neuro Histo

• Thick skin (palm), HE

  Difference between the different skin slides: Different keratinisation and different type of glands. There is no hair follicles in the palm
• Function of the skin

  • It is a receptor organ, works as a barrier and protects against pathogens and chemical and mechanical stress, regulates body temperature, reflects UV light, involved in production of vitamin D, cytokine and growth factors, protects against water loss, allows only hydrophilic molecules to penetrate
• Epithelium of the skin

  Stratified squamous keratinized epithelium
• Layers of the stratified squamous keratinized epithelium

  • Stratum basale
  • Stratum polygonale/spinosum
  • Stratum granulosum
  • Stratum lucidum
  • Stratum corneum
• Stratum basale


  Also called stratum germanitivum or cilindrocellular layer
• Stratum granulosum


  Contains keratohyaline granules
• Stratum lucidum


  Shiny due to eleidin (from keratohyaline)
• Connective tissue papillae


  • Provides more adhesion between dermal and epidermal layers, increases mechanical strength, provides larger surface area to nourish epidermal layer
• Receptors in connective tissue papillae


  • Free nerve endings
  • Meissner's corpuscles (mechanoreceptors)
• Malpighian layer


  Stratum basale and stratum spinosum together
• Cells in Malpighian layer

  • Melanocytes
  • Merkel's cells
  • Langerhan's cells
• Merkel's cells


  Special mechanoreceptors that sense light touch
• Langerhans cells


  Antigen presenting cells, part of mononuclear phagocytotic system, originate from monocytes, function in phagocytosis
• Melanocytes


  Melanin producing cells, originate from neural crest cells
• People with darker skin have more active melanin production and less active melanin breakdown enzymes compared to people with paler skin
• Melanocytes are found in iris, pigmented skin, hair follicles, meninges, ear</b>
• Knowing melanocyte locations is clinically important as melanomas can develop where melanocytes are concentrated
• Albinism diagnosis


  All optic nerve fibers cross, unlike in normal individuals where half cross and half don't
• Main parts of the dermis

  • Papillary layer
  • Reticular layer
• Subpapillary plexus/rete subpapillare


  Capillaries between papillary and reticular layers
• Rete cutaneum/subdermal plexus


  Capillaries between dermis and subcutis, important for skin thermoregulation
• Stratum reticulare


  Named due to special orientation of collagen fibers forming a meshwork, visible as Langer's lines
• Gland types


  • Exocrine
  • Endocrine
  • Endoepithelial
  • Exoepithelial
  • Unicellular
  • Multicellular
  • Secretory epithelium
• Sweat gland secretory mechanism

  Merocrine (goes to apical surface, exocytosis)
• Sebaceous gland secretory mechanism

  Holocrine (whole cell degenerates and dies)
• Odiferous gland secretory mechanism


  Apocrine (one part of cytoplasm leaves the cell)
• Sweat gland morphology


  Simple coiled tubular
• Darker sweat gland cross sections are the ducts, paler ones are the secretory portion
• Cells around sweat gland secretory portion

  Myoepithelial cells, can contract to help secretion
• Fat cell size is 50-100 um
• Normal epidermal turnover time is 52-75 days, in psoriasis it's 8 days
• Skin of the armpit, HE


  All skin glands (sweat, odiferous, sebaceous) are present
• Glands with wide lumen: Lactating mammary glands, uterine glands (secretory phase), prostatic glands (all apocrine)
• Hairy skin (scalp), HE


  Very large hair follicles protruding deep into subcutis
• Parts of the hair follicle

  • Cortex
  • Medulla
• Hair follicles are found everywhere except palms, soles, lips, nipples, genitalia
• Segments of the hair follicle

  • Inferior segment (stem)
  • Isthmus
  • Infundibulum
• Hair root


  Surrounded by hair follicle
• Role of hair


  • Thermoregulation, UV protection, sensory function
• Parts of the epithelial root sheath

  • Outer root sheath
  • Inner root sheath