Chemistry

• Skin


  An extensive organ covering the whole body with many functions
• Functions of the skin


  • Protection of internal organs
  • Maintain the homeostasis
  • Synthesis of vitamin D
  • Assist for defense mechanism against foreign bodies
• Types of skin


  • Thin skin
  • Thick skin

  
• Accessories of the skin


  • Nails
  • Hair
  • Sweat glands
  • Sebaceous glands
• Layers of the skin


  • Epidermis
  • Dermis
  • Hypodermis (subcutaneous tissue)

  
• Layers of the epidermis (thin skin)


  • Stratum basale
  • Stratum spinosum
  • Stratum desquamatum

  
• Layers of the epidermis (thick skin)


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

  
• Stratum basale


  Basal layer composed of simple columnar-cuboidal cells resting on the basement membrane, considered as germinal layer
• Stratum spinosum


  Layer formed by squamous cells which are large cells associated together with minute spines
• Stratum desquamatum


  Layer formed by sloughed cells of squamous type, continuously sloughing
• Stratum granulosum


  Layer formed by two rows of spindle shaped cells with Keratohyaline granules in the cytoplasm
• Stratum lucidum


  Glassy layer or zone with degenerated cells, no signs of cell outlines or nuclei
• Stratum corneum


  Horney layer formed by the presence of keratin, acts for protection of skin
• Dermis


  Layer formed by dense Connective Tissue with elastic fibers, collagen fibers, blood vessels, sensory nerves, sweat glands and sebecous glands, and numerous types of WBC

  
• Hypodermis


  Deepest layer of skin with loose Connective Tissue, Adipose tissue, blood vessels and the root shaft off hair follicles

  
• Components of the hair follicle


  • Shaft
  • Root
  • Bulb
• Structures within the hair follicle shaft


  • Outer cellular sheath
  • Inner cellular sheath
  • Medulla
• Hair follicle root


  Composed of basal cells responsible for division and replacement of the outer and inner sheath cells of the shaft
• Hair follicle bulb


  Occupied by Connective Tissue, blood vessels and nerve sensory
• Portions of the sweat glands


  • Stratified portion (tubular and transport)
  • Coiled or basal portion (secretory)
• The hypodermis contains a fatty tissue with blood vessels, which is a reservoir for protection from cold conditions
• Sensory organs


  Biologically identify sensations and are essential organs that participate in day-to-day activities, function by transmitting signals to the brain in response to the environment

  
• Five human sense organs


  • Eyes (sight)
  • Nose (smell)
  • Skin (touch)
  • Tongue (taste)
  • Ear (hearing)

  
• Sensory receptor cells


  Transduce physical stimuli to nerve signals interpreted by the brain
• Types of sensory receptors based on structure


  • Free nerve endings or dendrites
  • Encapsulated nerve endings
  • Specialised receptor cells
• Types of sensory receptors based on location of stimuli


  • Exteroreceptors (respond to external stimuli)
  • Interoceptors (respond to internal stimuli)

  
• Types of sensory receptors based on type of stimuli


  • Electroreceptors
  • Electromagnetic receptors
  • Thermoreceptors

  
• Eyes


  Sensory organ for sight, with a transparent outer layer (cornea) that bends light, an iris that acts like a camera shutter, and a lens that focuses light onto the retina

  
• Tongue


  Sensory organ for taste, with taste buds that detect sweet, bitter, salty, sour, and savoury tastes
• Nose


  Sensory organ for smell, with an olfactory cleft and over 400 smell receptors
• Skin


  Largest sensory organ, with specialized neurons that transmit sensations of touch, pressure, vibration, pain, temperature to the brain

  
• Ear


  Sensory organ for hearing, with an external ear, middle ear, and inner ear that transmit sound vibrations to the brain
• Hearing loss can be due to ageing or medical conditions