Feedback loops are control systems that the endocrine system uses to maintain hormone balance. They work like a thermostat that turns heating on when it’s too cold and off when it’s warm enough.
Negative Feedback Loops:
This is the most common type. When a hormone reaches a certain level, it signals the glands to stop or reduce production. For example, when thyroid hormone (T4/T3) levels are adequate, the pituitary produces less TSH, which tells the thyroid to slow down. When levels drop too low, TSH increases, signaling more production. This constant adjustment maintains balance.
Positive Feedback Loops:
These are less common and amplify a response rather than dampening it. The LH surge that triggers ovulation is a positive feedback loop – rising estrogen causes more LH release, which causes even more estrogen until ovulation occurs. After ovulation, the system resets.
The HPA Axis Example:
The Hypothalamic-Pituitary-Adrenal (HPA) axis is a classic feedback loop. The hypothalamus releases CRH, which tells the pituitary to release ACTH, which tells the adrenals to produce cortisol. When cortisol levels rise sufficiently, it signals back to the hypothalamus and pituitary to decrease CRH and ACTH production.
