Analyze Body Systems
& Homeostasis

Discover how organ systems work together to keep the body in balance through feedback and regulation.

GED Science

Levels of Organization

Your body is built in layers. Tiny cells group into tissues, tissues form organs, and organs join into organ systems that perform large jobs for the whole organism.

The Major Body Systems

Circulatory

Heart and blood vessels transport oxygen, nutrients, and waste.

Respiratory

Lungs exchange oxygen and carbon dioxide with the blood.

Digestive

Breaks food into nutrients the body's cells can absorb.

Nervous

Brain and nerves send rapid signals to control responses.

Endocrine

Glands release hormones for slow, long-lasting regulation.

Excretory

Kidneys remove waste and balance water in the blood.

Systems Work Together

No system works alone. When you run, your respiratory system pulls in more oxygen, your circulatory system pumps it faster, and your nervous system coordinates the timing.

What Is Homeostasis?

Homeostasis is the body's ability to keep its internal environment stable despite changes outside. Temperature, blood sugar, water, and pH are all held within a narrow safe range.

Temperature

Sweating cools you; shivering warms you.

Blood Sugar

Insulin lowers it; glucagon raises it.

Water Balance

Kidneys adjust how much water is kept.

The Negative Feedback Loop

Homeostasis works through negative feedback: when a value drifts away from its set point, the body responds to push it back toward normal.

Four Parts of Feedback

1

Stimulus. A change pushes a variable away from its set point (e.g. body gets too hot).

2

Receptor. Sensors detect the change and send a message.

3

Control center. The brain or a gland processes the signal and decides a response.

4

Effector. Muscles or organs act (e.g. sweat glands cool you) to restore balance.

Negative vs Positive Feedback

Most homeostasis uses negative feedback, which reverses a change. Positive feedback amplifies a change until a process completes.

	Negative Feedback	Positive Feedback
Effect on change	Reverses it	Amplifies it
Goal	Maintain stability	Finish an event
Frequency	Very common	Rare
Example	Body temperature control	Childbirth contractions

How to Analyze a Scenario

1

Identify the variable. What is being regulated (temperature, glucose, water)?

2

Find the stimulus. Did the variable go too high or too low?

3

Trace the response. Which systems detect and act on the change?

4

Confirm the result. Does the response push the variable back toward normal? If so, it's negative feedback.

Example: Getting Too Hot

Example: Blood Sugar After Eating

After a meal, blood glucose rises. The pancreas detects this and releases insulin, which signals cells to absorb glucose, lowering blood sugar back to normal.

Example: Water Balance

On a hot day with little water, blood becomes too concentrated. The brain releases ADH (antidiuretic hormone), telling the kidneys to keep more water, so less leaves as urine.

Dehydrated

More ADH released; kidneys retain water; little, dark urine.

Overhydrated

Less ADH; kidneys release water; lots of pale urine.

Common Mistakes

✕ Confusing feedback types

Negative feedback reverses a change; positive feedback amplifies it. Most homeostasis is negative.

✕ Ignoring teamwork

Forgetting that several systems must cooperate, not one alone, to maintain balance.

✕ Set point as fixed

Values fluctuate around a set point; homeostasis is dynamic balance, not a frozen value.

System & Variable Summary

Variable	Sensor / Control	Effector Response
Temperature	Hypothalamus	Sweat or shiver
Blood glucose	Pancreas	Insulin / glucagon
Water balance	Brain (ADH)	Kidneys retain/release
\( \text{O}_2 / \text{CO}_2 \)	Brain stem	Faster breathing

Question 1 of 5

A person's body temperature rises, so they begin to sweat, which cools them back to normal. This is an example of:

Sweating reverses the rise in temperature, pushing the value back toward its set point. Reversing a change is the defining feature of negative feedback.

Question 2 of 5

Which term describes the body's ability to keep a stable internal environment?

Homeostasis is the maintenance of a stable internal environment, such as keeping temperature near \( 37^\circ\text{C} \).

Question 3 of 5

After a meal raises blood glucose, the pancreas releases insulin. What is insulin's role in this loop?

Insulin is the effector signal: it causes cells to take up glucose, returning blood sugar toward normal. Glucagon would do the opposite when sugar is too low.

Question 4 of 5

In a feedback loop, which part actually carries out the response that restores balance?

The effector (such as sweat glands or muscles) performs the action that corrects the change. The receptor only detects it and the control center only decides.

Question 5 of 5

On a hot day with little water, the body releases ADH. What does this hormone cause the kidneys to do?

ADH tells the kidneys to keep more water, so less is lost as urine. This raises blood water content back toward normal and prevents dehydration.

Key Takeaways

1

Systems cooperate to perform large jobs and keep the body alive.

2

Homeostasis is stable internal balance despite outside change.

3

Negative feedback reverses changes through detect → signal → act.

4

Analyze scenarios by naming the variable, stimulus, and effector response.

Analyze Body Systems& Homeostasis

Levels of Organization

The Major Body Systems

Systems Work Together

What Is Homeostasis?

The Negative Feedback Loop

Four Parts of Feedback

Negative vs Positive Feedback

How to Analyze a Scenario

Example: Getting Too Hot

Example: Blood Sugar After Eating

Example: Water Balance

Common Mistakes

System & Variable Summary

Question 1 of 5

Question 2 of 5

Question 3 of 5

Question 4 of 5

Question 5 of 5

Key Takeaways

Analyze Body Systems
& Homeostasis