01Negative feedback
Negative feedback reverses a change to keep conditions near a set point (homeostasis). Blood glucose: high glucose → pancreas releases insulin → cells take up glucose → levels fall. Low glucose → glucagon → liver releases glucose.
Thermoregulation is another example: sweating when hot, shivering when cold.
02Positive feedback
Positive feedback amplifies a change until an end point. Childbirth: stretching cervix → oxytocin → stronger contractions → more stretching. Also blood clotting and fruit ripening (ethylene).
Positive feedback is rare in homeostasis because it drives things away from balance.
03Notebook box
Negative = counteract, stabilize. Positive = amplify, finish.
Worked example: In type 1 diabetes, beta cells don't make insulin. Which feedback loop fails and what happens? → The glucose-lowering negative loop; blood glucose stays high.