Homeostasis and hormonal control

• Homeostasis is the maintenance of a constant internal environment.
• A hormone is a chemical substance produced in minute quantities by an endocrine gland. It is transported in the bloodstream to target organ(s) where it exert its effects.
• structure in the skin involved in temperature regulation

  A) sweat gland

  B) sweat duct

  C) hair

  D) fats/adipose tissue

  E) blood capillaries

  F) nerve ending

  G) hair erector muscle

  H) hair follicle

  
• nerve endings = thermoreceptors
• Heat gained by the body:

  1. vigorous muscular exercise
  2. the consumption of hot food
  3. being in warm environments

  Excess heat needs to be removed so that one would not die from overheating.
• Heat loss by the body:

  1. through the skin
  2. by evaporation of water in sweat from the surface of the skin
  3. in the faeces and urine
  4. in the air that is exhaled

  The amount of blood flowing through the skin capillaries affects heat loss through the skin surface.
• 1. Skin arterioles dilate, increasing blood flow to the skin.
  2. More heat is carried to the surface
  3. When more blood flows to the skin surface, more heat is lost.
  4. Blood then flows away from the skin.
• 1. Skin arterioles constricts, decreasing blood flow to the skin.
  2. Less heat is carried to the surface
  3. When lessblood flows to the skin surface, lessheat is lost.
  4. Blood then flows away from the skin.
• The hypothalamus in the brain is responsible for monitoring and regulating the body's internal temperature, receiving information from the thermoreceptors in the skin and thermoreceptors in the hypothalamus.
• When body temperature begins to rise:

  1. Body and skin temperature increase
  2. Thermoreceptors in the skin and hypothalamus are stimulated
  3. Arterioles in the skin dilate, more blood flows to blood capillaries in the skin, and increase heat loss. Sweat glands become more active and more sweat is produced so more heat is lost. The metabolic rate also decreases.
  4. Blood temperature decreases back to the normal level
• When body temperature begins to fall:

  1. Body and skin temperature decreases
  2. Thermoreceptors in skin and hypothalamus stimulated
  3. Arterioles in the skin constrict, and less blood flows to blood capillaries in the skin, decreasing heat loss. Sweat glands become less active and less sweat is produced, less heat is lost. The metabolic rate increases and we will also start to shiver if very cold.
  4. Blood temperature increases to the normal level.