A hormone that is released from the thyroid gland (which is located in the neck)
Thyroxine
It stimulates the basal metabolic rate (BMR); this is the speed at which chemical reactions occur in the body when it is at rest
Thyroxine levels control
1. Negative feedback
2. TSH (thyroid-stimulatinghormone) released from the pituitary gland responsible for maintaining normal levels in the bloodstream
If the level of thyroxine is normal or too high
TRH production is inhibited in the hypothalamus
The release of TSH from the pituitary is therefore also inhibited
So less thyroxine is released from the thyroid gland
If the level of thyroxine falls below a normal level
TRH is released in the hypothalamus
This increases the release of TSH (thyroid-stimulating hormone) from the pituitary gland
TSH stimulates the thyroid to release more thyroxine
Conditions related to the thyroid gland
Hyperthyroidism, caused by an overactive thyroid gland secreting too much thyroxine into the bloodstream which causes an increase in BMR (weight) and protein synthesis
Hypothyroidism caused by an underactive thyroid gland secreting too little thyroxine into the bloodstream which can lead to heart and nerve problems, and death
