Hair, Feathers, Wool and Scales

• What are hair composed of?

  Dead keratinocytes in a cylindrical structure
• What is unique about hair?

  It is unique to mammals
• What are the main components of hair structure?

  • Central medulla
  • Thick cortex
  • Outer cuticle

  
• How does wool hair differ from typical hair structure?

  Wool hair has no medulla
• How many hairs does one follicle produce?

  One hair
• Where does the hair follicle sit?

  In the dermis, extending from the epidermis
• What is located at the deepest point of the hair follicle?

  The bulb
• What does the bulb of the hair follicle sit on?

  Dermal papilla
• What do epithelial cells at the dermal papilla do?

  Rapidly divide to produce keratinocytes
• What is the function of the hair follicle's associated sebaceous glands?

  To produce oil for hair lubrication

  
• What do arrector pili muscles do?

  They cause hair to stand up

  
• What are the two types of hair follicle arrangements?

  Simple and compound
• What characterizes simple hair follicles?

  One primary hair known as guard hair
• Which animals typically have simple hair follicles?

  Horses, cattle, pigs, and humans
• What characterizes compound hair follicles?

  One primary hair plus multiple secondary hairs
• Which animals typically have compound hair follicles?

  Dogs, cats, sheep, and goats
• What are the three basic hair forms?

  • Stiff straight guard hairs (topcoat)
  • Fine wavy wool hairs (undercoat)
  • Thick long tactile hairs (sensory function)
• How do guard hairs typically lie against the skin?

  They run in tracts of the same direction
• What is the function of tracts of guard hairs?

  To promote rainwater runoff
• What are some species-specific modifications of guard hairs?

  Mane, tail, and fetlock tufts of horses
• What characterizes wool hairs?

  They are soft, thin, and wavy
• What is the function of wool hairs?

  To trap air for insulation
• Which animals have wool hairs?

  Sheep, alpacas, cashmere goats, Angora rabbits
• Where are tactile hairs mostly found?

  On the face and head
• What surrounds the follicle of tactile hairs?

  A dermal sheath containing nerve endings
• What is the function of the venous sinus surrounding tactile hairs?

  To amplify stimulation
• What is the growth cycle of guard and wool hairs?

  They have a limited lifespan and are gradually shed
• How does seasonal shedding occur in healthy animals?

  Hairs have offset growing cycles
• What regulates seasonal shedding?

  The pineal gland
• What factors influence hair shedding?

  Day length, temperature, and nutrition
• What are the phases of the hair growth cycle?

  1. Anagen: Growing phase
  2. Catagen: Transition phase
  3. Telogen: Resting phase
• What happens during the anagen phase?

  Hair follicles are actively growing
• What occurs during the catagen phase?

  Growth slows and follicle atrophies
• What happens during the telogen phase?

  Growth stops and hair can be shed
• What are the functions of hair?

  1. Protection
  2. Water resistance
  3. Thermoregulation/insulation
  4. Communication/camouflage
  5. Sensory function
• How do hair provide protection?

  By covering sensitive structures with keratin
• How do sebaceous glands contribute to water resistance?

  By producing oily secretions
• How do wool hairs assist in thermoregulation?

  By trapping air for insulation
• What role do colors play in hair functions?

  They aid in communication and camouflage
• What is the sensory function of tactile hairs?

  They detect environmental stimuli