Hormones and Negative Feedback
A hormone travels in the blood, acts slowly and reaches every organ, which is the opposite trade-off from a nerve impulse. Negative feedback holds a quantity near a set point by acting against whichever way it moved.
What a learner can do afterwards
- Compares nervous and hormonal control on speed, duration and how the message travels.
- Names the gland that releases a given hormone and the organ that responds to it.
- Traces one negative feedback loop and says what would happen if the loop were cut.
1 · Read
Nerves fire fast, brief, and down a wire to one place. Hormones do the opposite trade: they travel slowly in the blood, act slowly, last longer, and reach every organ. Only organs with the matching receptor respond, so the message lands where it should.
The thyroid shows the loop. The pituitary tells the thyroid to release its hormones, and rising hormone levels signal the brain to stop pushing. That stop signal is negative feedback: the result switches off its own cause.
Every loop guards a set point. A sensor watches the level, a control centre compares it with normal, and an effector pushes back against any drift. Cut the feedback wire and the gland never hears stop, so the hormone keeps building past normal. Positive feedback does the reverse and amplifies a change, as in childbirth.
Name the gland and the responder every time. For thyroid control the pituitary speaks and the thyroid answers, and the rising hormones quieten the pituitary in return.
Hormones ride the blood to matching receptors while feedback holds each level near its set point.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.