ACARA v9 CONTENT DESCRIPTION “compare the role of body systems in regulating and coordinating the body’s response to a stimulus, and describe the operation of a negative feedback mechanism”
Builds on the idea that organ systems each carry a task. Here those systems work together to sense a change and respond to it, and we meet the rule that keeps internal conditions steady: negative feedback.
Sensing and responding to a stimulus
A response to a change in the surroundings runs along a chain. A receptor detects the stimulus and sends a signal. A coordinating system, either the nervous system or the endocrine system, processes that signal and decides what to do. An effector, usually a muscle or a gland, then carries out the response. Reading the chain in order shows how separate body systems cooperate to act on the world.
From stimulus to response
A response runs along a chain. Step the signal from the stimulus through to the response.
Stimulus: a change in the surroundings, such as a hand touching a hot surface. The chain runs in order — a receptor detects the change, a coordinating system decides what to do, and an effector carries it out. The nervous and endocrine systems both work at the coordination stage.
Two systems that coordinate
The nervous system and the endocrine system both coordinate responses, but in different ways. The nervous system sends fast electrical signals along nerves, so the response is almost immediate but short-lived. The endocrine system releases hormones into the blood, so its signals travel more slowly, reach many parts of the body, and last longer. Quick reactions rely on nerves; steady, ongoing control relies on hormones.
Two systems coordinate a response
The nervous and endocrine systems both coordinate the body. Toggle between them to compare how each signal travels.
The nervous system sends fast electrical signals along nerves. The response arrives almost at once but does not last long, which suits sudden actions such as pulling a hand back from heat.
Negative feedback holds a set point
Many internal conditions are kept near a set value. Body temperature sits near 37 degrees. If the body becomes too hot, it sweats and widens skin blood vessels to lose heat; if it becomes too cold, it shivers and narrows those vessels to keep heat in. In each case the response opposes the change and pushes the value back toward the set point. This opposing action is called negative feedback.
Negative feedback: body temperature
Push the temperature away from the set point, then correct it. The body opposes the change to return to 37 degrees.
At the set point near 37 degrees the body holds steady. Push the temperature away and watch which response the body uses to bring it back.
The same rule controls blood glucose
Blood glucose is regulated by the same principle with different hormones. After a meal, glucose rises, and insulin moves it out of the blood. Between meals, glucose falls, and glucagon releases stored glucose back into the blood. High triggers a lowering response, low triggers a raising response, and the level is held near a steady value. The variable changes, but the rule is identical to temperature control.
The same rule: blood glucose
Blood glucose is held near a set point too. Push it away and the matching hormone restores it.
At the set point the level holds steady. Push it high or low and watch which hormone the body uses to bring it back. The rule is the same as for temperature.
Why negative feedback matters
Negative feedback works because it always acts against a change. A value nudged above the set point triggers a response that lowers it; a value nudged below triggers a response that raises it. The variable swings back, may overshoot a little, and settles near the set point. Without this opposing action, a small change would never be corrected and the value would drift away, which is why feedback is essential for keeping the body in balance.
Why negative feedback keeps things stable
Both paths start with the same nudge away from the set point. Toggle feedback to see what each path does over time.
With negative feedback, every nudge is opposed, so the variable swings back, overshoots a little, and settles near the set point. This is how the body keeps temperature and glucose stable.
Why this matters
Seeing a response as a pathway, and stability as negative feedback, lets us explain how the body coordinates itself rather than just naming its parts. The same idea links a reflex to a hormone, a hot day to a meal, and explains why internal conditions stay remarkably steady. It is one rule that runs through many of the body systems at once.
Quick self-check
1. What is the correct order of the response pathway to a stimulus?
2. How does the nervous system differ from the endocrine system in coordinating a response?
3. In negative feedback control of body temperature, what happens when the body becomes too hot?
4. When blood glucose rises after a meal, which hormone lowers it back toward the set point?
5. Why does negative feedback keep a variable near a stable set point?