7.2.6Unit 6: Practical Skills in Biology II
The Role of Adrenaline — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 4 parts Lesson 28 of 48 Unit quiz
Part 1 of 4Triggering the Response
1
Stress, fear or excitement is detected and sympathetic neurones stimulate the adrenal medulla, part of the adrenal gland.
2
The adrenal medulla secretes adrenaline into the blood, which carries it around the whole body.
3
Adrenaline binds to specific receptors on the cell surface membranes of its target organs.
4
The target cells respond, and the combined effects prepare the body for rapid action.
5
When the threat has passed secretion falls and the effects fade, as the parasympathetic nervous system restores the resting state.
Part 2 of 4Effects of Adrenaline
Heart
- Adrenaline acts on the sinoatrial node, increasing the frequency of excitation and so raising the heart rate.
Blood flow
- Arterioles supplying the gut and skin constrict, which diverts blood toward the muscles.
Respiration
- More oxygen and glucose reach muscle cells, increasing aerobic respiration and the release of energy.
Brain
- Blood flow to the brain stays constant, as it must always receive a steady supply of oxygen and glucose.
Symptoms
- The typical signs are a faster heartbeat, sweating and a dry mouth.
Part 3 of 4How Adrenaline Works in Cells
How Adrenaline Works in Cells
Receptor
- Adrenaline cannot cross the membrane, so it binds to a receptor on the outside of the cell.
Second messenger
- Binding activates a second messenger inside the cell, called cyclic AMP, which is made from ATP.
Cascade
- Cyclic AMP activates protein kinases, which trigger a chain of enzyme reactions.
Outcome
- The cascade changes enzyme activity, and it can also affect transcription factors and gene expression.
| Feature | Nervous control | Hormonal control |
|---|---|---|
| Signal | Electrical impulse | Chemical hormone |
| Route | Neurones | Blood |
| Speed | Very fast | Slower |
| Duration | Short-lived | Longer-lasting |
Part 4 of 4Exam Checklist & Tips
7.2.6 – Key Points for the Exam
- Adrenaline A hormone from the adrenal medulla that prepares the body for fight or flight.
- Adrenal medulla The inner part of the adrenal gland that secretes adrenaline.
- Second messenger A molecule inside a cell that relays the signal from a hormone bound at the surface.
- Cyclic AMP A second messenger made from ATP.
- Target organ An organ with receptors for a particular hormone.
Common Mistakes
- Saying adrenaline enters cells directly; it works through a surface receptor and second messenger.
- Stating that blood flow to the brain falls during fight or flight.
- Describing hormones as faster than nerve impulses.
- Forgetting that adrenaline is released after nervous stimulation of the adrenal medulla.
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