Connect endocrine signals with homeostasis
Describe endocrine coordination using ADH, glucagon and insulin, linking blood-borne hormones to target cells.
Section 15.1 · Control and coordination in mammals
A Level; Cambridge International Biology 9700, 2028–2030. Written answers are self-checked; this is not practical-skills certification.
Before you begin
- A control pathway links a stimulus, receptor, coordination system and response.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Why can a hormone affect one cell type but not another?
What you will learn
- Describe endocrine glands releasing hormones into blood
- Use ADH, glucagon and insulin as examples of hormones acting on target cells
Nervous and endocrine coordination
| Feature | Meaning |
|---|---|
| Nervous | Electrical impulses along neurones; neurotransmitter at synapses |
| Endocrine | Hormones transported in blood to cells with appropriate receptors |
| Typical pattern | Nervous responses are rapid and localised; endocrine responses are often slower and longer-lasting |
| Examples | ADH, glucagon and insulin are hormones |
Build the mechanism
Endocrine glands release hormones into the blood. A hormone reaches many tissues, but only target cells with an appropriate receptor respond. ADH, glucagon and insulin are endocrine signals already encountered in water and blood-glucose control: ADH affects water reabsorption, while insulin and glucagon have opposing effects on blood glucose through different target-cell responses.
Keep the sequence precise
A hormone is the chemical signal, not the gland or the responding organ. Hormones circulate in blood, but this does not mean that every cell responds. The appropriate receptor and downstream response determine target-cell specificity.
Pause and explain
A drug blocks insulin receptors on one tissue while blood insulin remains normal. Predict what happens to that tissue’s response.
Worked example
A hormone circulates past two cell types, but only one changes its activity. Explain the difference.
Show the worked solution
- Both cell types are exposed through the blood.
- Only the responsive cells have receptors that bind the hormone and initiate a response.
Answer Only cells with the appropriate receptor are target cells; exposure to blood alone does not guarantee a response.
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Trace how a pancreatic hormone can coordinate a response in liver cells.
Give me a hint
Name the first event, then follow each link in order.
Compare my reasoning
- The gland releases a hormone into blood.
- The hormone reaches liver cells with matching receptors and changes their activity.
The pancreas releases the hormone into blood. It reaches liver cells, and cells with appropriate receptors respond, helping coordinate a change in blood glucose.
Look for these in your work
- Mechanism stated
- Steps linked in order
ADH is measured in blood, but a target-cell response changes water permeability. Link the hormone to the response.
Give me a hint
Use the terms in the question and state what changes.
Compare my reasoning
- ADH travels in the blood to target tissues.
- Receptor binding changes the activity of cells in the water-control pathway.
ADH is a blood-borne endocrine signal. It binds receptors on target cells in the water-control pathway and changes their response, including collecting-duct water permeability.
Look for these in your work
- Evidence interpreted
- Biological direction explained
A drug blocks insulin receptors on one tissue while blood insulin remains normal. Predict what happens to that tissue’s response.
Give me a hint
Apply the mechanism to the new context without adding unsupported claims.
Compare my reasoning
- The hormone is still present in blood.
- Blocked receptors prevent normal target-cell detection of the signal.
That tissue will show a reduced or absent insulin response because its receptors cannot detect the hormone normally; other tissues with available receptors may still respond.
Look for these in your work
- Mechanism applied
- Limits preserved
Common mistakes
- Saying a hormone affects every cell it reaches
- Confusing the hormone with its target organ
What can you explain now?
Why can a hormone affect one cell type but not another?
Compare with the explanation
Only the target has the appropriate receptor
Hormone binding to its receptor initiates the target-cell response.
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Make it stick
What makes a cell a target of a circulating hormone?
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