Thyroxine

• Metabolic rate- the rate at which the energy stored in the food in transferred by reactions in the body.E.g used in repsiration, digestion, protein synthesis

  -People who transfer energy more slowly have a lower metabollic rate.They have excess energy which is stored as fat. Their masses tend to increase.

  -People who transfer energy more quickly have a higher metabolic rate. They have do not have excess energy to store as fat. Their mass tend to decrease.
• If thyroxine levels in the blood fall to low levels

  -The hypothalamus detects this and releases TRH.

  -TRH stimulates the pituitary gland and releases TSH.

  -TSH stimulates the thyroid gland to produce thyroxine.

  -Thyroxine levels start to rise.
• If throxine levels in the blood is too high

  -The hypothalamus detects this and inhibits TRH.

  -The drop in TRH stops the pituitary gland producing TSH.

  -The drop in TSH stops the thyroid gland producing throxine.

  -Thyroxine level starts to fall.
• Thryoxine has two effects

  • Causes the heart to contract more strongly and rapidly
  • increases the rae at which protein and carbohydrate are broken down