Homeostasis and Negative Feedback

Exam Revision

What is homeostasis?

Homeostasis is the maintenance of a stable internal environment in the body, despite changes in external conditions.

What is negative feedback?

Negative feedback is a control process that detects changes in the body and triggers responses that reverse those changes, restoring balance (homeostasis).

How does negative feedback maintain homeostasis?

It detects when a condition becomes too high or too low and activates responses that bring it back to the normal level.

What is vasoconstriction?

Vasoconstriction is when blood vessels near the skin narrow to reduce blood flow, decreasing heat loss from the body.

How does shivering help increase body temperature?

Shivering involves rapid muscle contractions that generate heat to warm the body.

What happens when body temperature drops? (warming responses)

The body responds with shivering and vasoconstriction to increase body temperature and return it to normal.

What is vasodilation?

Vasodilation is when blood vessels near the skin widen to increase blood flow, helping the body lose heat.

How does sweating cool the body?

Sweat is produced and evaporates from the skin, removing heat energy and cooling the body.

What happens when body temperature rises? (cooling responses)

Blood vessels undergo vasodilation and sweating increases to lose heat and lower body temperature.

Why do these responses help maintain homeostasis?

They reduce body temperature back to its normal level, keeping internal conditions stable.

What is the negative feedback loop for temperature regulation?

Negative feedback reverses the change and returns body temperature to its normal set point (homeostasis).

Receptors: Detect temperature change in skin and brain

Coordinator (brain/hypothalamus): Processes information

Effectors: Muscles, sweat glands, and blood vessels

Response:

If too hot → sweating + vasodilation → temperature decreases

If too cold → shivering + vasoconstriction → temperature increases

This returns body temperature to normal (homeostasis)

What is the role of the hypothalamus in temperature control?

It acts as the body's thermostat, detecting temperature changes and coordinating responses to maintain homeostasis.

What conditions are controlled by homeostasis and why?

Homeostasis controls conditions such as body temperature, blood glucose concentration, and water levels to keep them within narrow limits so body cells can function properly.

Which organ systems help maintain homeostasis?

The skin, kidneys, liver, endocrine system, nervous system, and sensory system all work together to maintain a stable internal environment.

How does a negative feedback loop maintain homeostasis?

It compares the current condition to a set point or normal range. If a change is detected, it triggers responses that counteract the change and return the body back to the set point.

What are examples of negative feedback in temperature regulation?

If too cold, the body shivers to increase temperature. If too hot, the body sweats to decrease temperature. Both return temperature to normal.

What happens in negative feedback when blood glucose is too high?

Body cells take up glucose from the blood, lowering blood glucose back to normal.

What happens in negative feedback when blood glucose is too low?

Stored glucose is released into the blood, raising blood glucose back to normal.

What is positive feedback?

Positive feedback is a process where a response reinforces or amplifies the change detected, making it stronger rather than reversing it.

How is positive feedback different from negative feedback?

Negative feedback reverses changes to maintain stability, while positive feedback amplifies changes and moves the system further from the starting point.

How does positive feedback work in childbirth?

Stretching of the uterus triggers oxytocin release, which increases contractions, causing more stretching and more oxytocin release until birth occurs.

Give examples of positive feedback.

Childbirth (oxytocin and contractions), lactation (milk production during feeding), and blood clotting (platelets attract more platelets).

What is the endocrine system?

The endocrine system is a collection of glands that produce and release hormones into the bloodstream.

What are hormones?

Hormones are chemical messengers that travel in the blood to target cells to produce a response.

What are target cells?

Target cells are cells with specific receptors that match a particular hormone.

What is the difference between nervous and endocrine responses?

Nervous responses are fast and short-lasting, while endocrine responses are slow but long-lasting.

Why is the endocrine system response slower than the nervous system?

Because hormones travel through the bloodstream, which is slower than electrical nerve impulses.