Homeostasis & Feedback

Homeostasis is keeping a relatively constant internal environment so the body works at its best. It runs on a stimulus–response pathway:

$$\text{stimulus} \to \text{receptor} \to \text{control} \to \text{effector} \to \text{response}$$

• A stimulus is a change in a condition.
• Receptors detect it and send a message (nerve impulse or hormone).
• Effectors (muscles or glands) carry out the response.

Negative feedback

Most homeostasis uses negative feedback: the response opposes the original change, bringing the condition back toward its set point. ('Negative' means opposing, not bad.)

Negative feedback: the response loops back to cancel out the original stimulus.

Example: blood glucose rises after a meal → the pancreas releases insulin → glucose falls back to normal.