Depth 1 · 64 s
The car horn
A horn blasts and you jump back before you think. How the body's stress alarm works - adrenaline in seconds, cortisol if it lasts, and a brake that calms you - and why it's useful.
About this video
You step off the pavement and a car horn blasts. Before you have thought about it, you have jumped back. Your heart is pounding, you are breathing fast and your hands shake a little, and a few minutes later you are calm again. That is the stress response: the quick changes the body makes when something seems like a danger, or a challenge you must deal with.
It starts in the brain. A part of the brain that handles feelings spots the danger and signals the adrenal glands, two small glands on top of the kidneys. They pour adrenaline, a hormone carried by the blood, into the bloodstream. Within moments the heart beats faster and blood pressure rises, breathing speeds up, muscles tense, you may sweat, and sugar and fat from the body's stores go into the blood as fuel. About a hundred years ago the American scientist Walter Cannon called this the fight or flight response. Some people freeze instead, going still for a moment.
If the danger doesn't pass quickly, a slower chain takes over: the brain signals the pituitary gland, which signals the adrenal glands to make cortisol. Cortisol keeps the body on alert and keeps energy coming. When the danger has gone, cortisol falls, and another part of the nervous system works like a brake, slowing the heart and breathing.
Cortisol is not a "bad hormone". In a stressful moment it does a useful job. The stress response is built for short bursts: jumping back from a car, a race, an exam. The trouble starts only when the alarm doesn't switch off for weeks or months. This video explains the stress response on Knaph, from the Health Level 1 lesson The Stress Response.
This video shows depth 1 of Stress response.
Learn Stress responseTranscript
- 0:00A horn blasts. You jump back before you think. Your heart pounds, then you calm down.
- 0:08The brain signals the adrenal glands, and they pour adrenaline into the blood. Within moments, your heart races, you breathe fast, your muscles tense, and fuel goes into the blood.
- 0:20Walter Cannon called it fight or flight. Some people freeze instead.
- 0:27If the danger lasts, a slower wave comes. The pituitary gland signals the adrenal glands to make cortisol, which keeps you alert.
- 0:38Adrenaline spikes, cortisol holds, and when the danger has gone, a brake calms the body.
- 0:48Is cortisol bad for you? No. It does a useful job. The trouble is an alarm that stays on for weeks.
- 0:57An alarm, built for short bursts.