Hormones and Negative Feedback
A hormone travels in the blood, often acts more slowly and for longer than a nerve impulse, and reaches every organ, which is the opposite trade-off from a nerve impulse. Negative feedback usually 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
Nerve signals are usually fast and brief and travel to a specific place. Hormones often act more slowly and last longer, but speed and duration vary. Hormones ride the blood to their targets, while nerves use wires. That trade shapes this whole topic.
Hormones ride the blood, so the blood can carry a hormone to every organ. Only cells with the matching receptor answer. Delivery is broad, response is narrow.
Rising thyroid levels usually ease the pituitary drive instead of shutting it off fully. Less drive means less release. The level settles near its set point.
A feedback loop has three jobs. A sensor watches the level. A control centre compares it with normal. An effector pushes back against drift.
In this thyroid model a cut link can leave release on, so levels may rise past normal. Other loops fail in other ways. Positive feedback runs the other way and amplifies change, as in childbirth.
Name the gland and the responder every time. For thyroid control the pituitary speaks and the thyroid answers, and rising hormones ease the pituitary in return.
Hormones ride the blood to matching receptors while feedback usually eases release near its set point.
Original readings written for this topic, plus a retained Khan Academy article on feedback loops. Videos from TED-Ed and Cognito; terms unknown.
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.