A waiter asks “Room for dessert?” Looking at the plates in front of you and feeling stuffed you say, “No thanks, we’re full.”
Different regulatory systems in the body work similarly. The end product is a signal to stop making the “more” signal. Adequate thyroid hormone tamps down the first step in the “make more thyroid hormone” sequence. Norepinephrine and epinephrine bind to alpha-2 receptors on the releasing neuron to say “stop ramping up the fight-or-flight response, we’ve done enough.”
TL;DR: A->B->C->D. D limits production of A so there’s not too much D.
They continuously work to keep your body in it’s normal state. Whether it’s to reduce/increase your body temperature 98.6°F, slow your heart to its resting rate, or returning any system to its normal operating parameters. Basically, negative feedback loops bring you back to a state of homeostasis.
You also have positive feedback loops that push your body further and further away from normal. Lactating, giving birth, orgasms, and blood clotting are examples of positive feedback loops. They take your body further away from homeostasis.
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