explain concept of negative feedback how ir relates to the hormones involved in thyroxine release?

Answer 1

In the case of Thyroxine, T3 and T4 levels are controlled by TSH, Thyroid Stimulating Hormone. In case of hyperthyroidism, TSH levels are suppressed since T3 and T4 are high. In the case of hypothyroidism, TSH levles are elevated because T3 and T4 levels are below normal. This is called negative feed-back. Negative feed-back is used in many control systems like temperature controllers, liquid level controllers and so on.

A positive feed-back increases the signal (for example, a good pat on the back is a positive feed-back for all of us and motivates us to do better). In a circuit with positive feed-back, the circuit becomes unstable.