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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Adrenaline Effects
Adrenaline (also called epinephrine) is a hormone that plays a crucial role in your body's immediate response to stress. When you're scared, excited, or in danger, your adrenal glands release adrenaline into your bloodstream, triggering a series of changes that prepare your body to either fight the danger or run away from it – the famous "fight-or-flight" response.
Key Definitions:
Adrenaline is produced in the adrenal glands, which sit on top of your kidneys. Specifically, it's made in the inner part of the adrenal gland called the adrenal medulla. When your brain perceives danger or stress, it sends signals to your adrenal glands to release adrenaline into your bloodstream, where it can quickly travel throughout your body.
Your body releases adrenaline in response to:
When adrenaline enters your bloodstream, it has dramatic effects on your heart and blood vessels. These changes help deliver more oxygen and nutrients to your muscles and brain when you need to respond quickly.
Adrenaline binds to receptors on heart cells, causing several important changes:
Adrenaline makes your heart beat faster (tachycardia), sometimes up to 2-3 times the normal rate. This helps circulate blood more quickly throughout your body.
Your heart contracts more forcefully, ejecting more blood with each beat. This increases your cardiac output - the amount of blood pumped per minute.
Adrenaline causes blood vessels to constrict (narrow) in your digestive system and skin, but dilate (widen) in your muscles and lungs. This redirects blood to where it's most needed during stress.
Mountain climbers often experience natural adrenaline rushes when facing challenging or dangerous situations. Researchers studying climbers on Mount Everest found that during particularly difficult sections, climbers' heart rates increased by up to 85% above their resting rates, even though they were moving slowly. This demonstrates how adrenaline prepares the body for action even before intense physical activity begins. The increased cardiac output helps deliver oxygen more effectively at high altitudes where oxygen is scarce.
The fight-or-flight response is your body's ancient survival mechanism that prepares you to either confront a threat or escape from it. Adrenaline is the key hormone that triggers this response.
Within seconds of adrenaline release, you might experience:
Adrenaline quickly mobilises energy reserves:
Adrenaline works through a sophisticated signalling system that allows it to affect multiple organs simultaneously.
Adrenaline doesn't actually enter cells to cause its effects. Instead, it works as a messenger that triggers changes from outside the cell:
Adrenaline (epinephrine) is used as a life-saving medication for several conditions:
| Body System | Normal State | With Adrenaline |
|---|---|---|
| Heart Rate | 60-100 beats per minute | Can increase to 150-180 beats per minute |
| Blood Pressure | Around 120/80 mmHg | Increases significantly |
| Breathing | 12-20 breaths per minute | Faster and deeper |
| Blood Glucose | 4-7 mmol/L | Increases as glycogen is broken down |
| Digestion | Active | Slowed or temporarily halted |
| Pupils | Normal size | Dilated |
Adrenaline works alongside the sympathetic nervous system, which is part of your autonomic (involuntary) nervous system. While nerve signals travel quickly along neurons, adrenaline's effects last longer and reach parts of the body that aren't directly connected to sympathetic nerves.
The release of adrenaline is controlled by a region of your brain called the hypothalamus, which acts as a command centre during stress. When the hypothalamus detects danger (either from your senses or your thoughts), it triggers both:
This dual-action system ensures your entire body responds quickly and comprehensively to threats.
There are documented cases where people have performed extraordinary feats of strength during emergencies, like lifting cars to free trapped individuals. While these stories are sometimes exaggerated, the science behind them is real. Adrenaline can temporarily increase muscle strength by:
However, this comes at a cost - people often experience muscle soreness, fatigue and even injury afterwards as the protective effects of adrenaline wear off.
Adrenaline prepares your body for action through multiple coordinated effects:
These effects collectively prepare your body to either fight a threat or flee from danger - an ancient survival mechanism that continues to protect us today, even if our modern "threats" are often more psychological than physical.
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