The mechanism is called a negative feedback loop, like a thermostat on a furnace that turns on when the temp drops below a set level, then turns off when the temp reaches that level.
Individual organs regulate the release of their own hormones, or depend on the pituitary to give them a signal to release the trophic hormone
We will call TH the trophic hormone
We will call X the hormone itself
So, TH (X) is the releasing substance for hormone (X)
Example: Brain detects thyroid level too low
1) Hypothalamus releases TSHRH (thyroid stimulating hormone releasing hormone), gives order to pituitary.
2) Pituitary receives command from TSHRH to release TSH (thyroid stimulating hormone), gives order to thyroid
3) Thyroid receives command from TSH to make thyroid hormone (thyroxine) and release into bloodstream, which it does.
4) Thyroid levels rise to adequate level. Feedback turns off TSHRH. Turns off TSH.
5) Thyroid stops making thyroid hormone. Sits dormant until ordered to make more thyroid and loop starts over again.
When the thyroid doesn't make thyroxine no matter how much it is ordered to make more, that is called PRIMARY failure. The organ itself is at fault
When a perfectly good thyroid doesn't make any thyroxine because it doesn't get any TSH telling it to make more, this is called SECONDARY failure, usually a problem with the pituitary that won't pass on TSH command. its like a perfectly good furnace with an inoperative thermostat
Source: I am a pharmacist.
Individual organs regulate the release of their own hormones, or depend on the pituitary to give them a signal to release the trophic hormone
We will call TH the trophic hormone
We will call X the hormone itself
So, TH (X) is the releasing substance for hormone (X)
Example: Brain detects thyroid level too low
1) Hypothalamus releases TSHRH (thyroid stimulating hormone releasing hormone), gives order to pituitary.
2) Pituitary receives command from TSHRH to release TSH (thyroid stimulating hormone), gives order to thyroid
3) Thyroid receives command from TSH to make thyroid hormone (thyroxine) and release into bloodstream, which it does.
4) Thyroid levels rise to adequate level. Feedback turns off TSHRH. Turns off TSH.
5) Thyroid stops making thyroid hormone. Sits dormant until ordered to make more thyroid and loop starts over again.
When the thyroid doesn't make thyroxine no matter how much it is ordered to make more, that is called PRIMARY failure. The organ itself is at fault
When a perfectly good thyroid doesn't make any thyroxine because it doesn't get any TSH telling it to make more, this is called SECONDARY failure, usually a problem with the pituitary that won't pass on TSH command. its like a perfectly good furnace with an inoperative thermostat
Source: I am a pharmacist.