Cooling Down

• what is vasodilation


  arterioles near the skin surface dilate when temperature increases

  • vessels connecting arterioles and venues constrict (arteriovenous shunt vessels)
  • forces blood through capillary networks close to surface of the skin
  • skin flushes, and cools due to increased radiation
• increased sweating


  • in humans and horses, sweat glands span entire body
  • as sweat evaporates from the body, heat is lost, cools the blood below the surface
  • in some animals sweat glands are reduced to less hairy areas, so mouths open and pant, so heat is lost as water evaporates
• insulating effect of hair/feathers


  • erector pilli muscles in skin relax, so hairs lie flat to the skin, avoids trapping an insulating layer of air - little effect in humans
• anatomical adaptations


  • minimise effect of high temperatures
  • maximise ability of cooling down
  • relatively large SA:V ratio to maximise cooling
  • pale fur or feathers to reflect radiation