How do hormones coordinate the body, and how is this different from nervous control?
Describe hormonal coordination and compare it with nervous control, using adrenaline as an example
A focused answer to the O-Level Biology outcome on hormonal coordination. What a hormone is, how the endocrine system works, the effects of adrenaline, and how hormonal control compares with nervous control.
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What this dot point is asking
SEAB wants you to describe how the body is coordinated by hormones (the endocrine system): what a hormone is, how it travels and acts, and the effects of adrenaline as a key example. You should also be able to compare hormonal control with nervous control on how the message travels, its speed, and how long the effect lasts.
The answer
What a hormone is
A hormone is a chemical messenger that is made and released by an endocrine gland, carried in the blood, and acts on target organs elsewhere in the body. The endocrine glands together make up the endocrine system.
Examples of endocrine glands and their hormones include the pancreas (insulin and glucagon, controlling blood glucose) and the adrenal glands (adrenaline).
Adrenaline, the "fight or flight" hormone
Adrenaline is released by the adrenal glands (above the kidneys) when a person is frightened, excited or stressed. It prepares the body for sudden action. Its effects include:
- Increasing the heart rate, so blood is pumped faster.
- Increasing the breathing rate and depth, taking in more oxygen.
- Raising the blood glucose level (by causing glycogen to break down to glucose).
- Widening the pupils and diverting blood to the muscles.
These changes deliver more oxygen and glucose to the muscles, so they can respire faster and release more energy quickly, to fight or run away. This is the fight or flight response.
Comparing nervous and hormonal control
The body has two coordination systems, which differ:
| Feature | Nervous control | Hormonal control |
|---|---|---|
| How the message travels | Electrical impulse along neurones | Chemical (hormone) in the blood |
| Speed | Very fast | Slower |
| Duration of effect | Short-lived | Longer-lasting |
| How widespread | To specific parts | Can affect many organs |
Nervous control is for fast, brief, precise responses (like a reflex); hormonal control is for slower, longer, more widespread changes (like growth or blood glucose control).
Examples in context
Example 1. Before an exam or a race. Feeling nervous before a test or the start of a race releases adrenaline, so your heart pounds and you breathe faster. This readies your body for action, even though you only need to sit or run, showing the fight or flight response.
Example 2. Insulin as a slower hormone. Unlike the rapid burst of adrenaline, insulin works steadily to lower blood glucose over a longer period after a meal. Both are hormones, but they show how hormonal effects can be brief or sustained.
Try this
Q1. Define a hormone. [2 marks]
- Cue. A chemical messenger made by an endocrine gland, carried in the blood, that acts on target organs to produce a response.
Q2. Name the gland that releases adrenaline and state one of its effects. [2 marks]
- Cue. The adrenal gland; it increases the heart rate (or breathing rate, or blood glucose).
Q3. State two differences between nervous and hormonal control. [2 marks]
- Cue. Nervous control uses electrical impulses along neurones, is fast and short-lived; hormonal control uses chemicals in the blood, is slower and longer-lasting.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original5 marksAdrenaline is released when a person is frightened. (a) Name the glands that release it. (b) Describe three effects of adrenaline on the body. (c) Explain how these effects prepare the body for action.Show worked answer →
(a) Adrenaline is released by the adrenal glands (above the kidneys).
(b) Three effects: it increases the heart rate; it increases the breathing rate (and depth); it raises the blood glucose level (by causing glycogen to be broken down to glucose). Other accepted effects include widening the pupils and diverting blood to the muscles.
(c) These effects prepare the body for action (the fight or flight response): a faster heart rate and deeper breathing deliver more oxygen and glucose to the muscles, and the higher blood glucose provides fuel for respiration, so the muscles can release more energy quickly to fight or run away.
Markers reward the adrenal glands, three correct effects, and the explanation that they supply the muscles with more oxygen and glucose for rapid energy release.
Original4 marksCompare nervous control and hormonal (chemical) control in terms of how the message travels, the speed, and how long the effect lasts.Show worked answer →
In nervous control, the message travels as an electrical impulse along neurones; it is very fast; and the effect is usually short-lived.
In hormonal control, the message travels as a chemical (a hormone) in the blood; it is slower to take effect; and the effect usually lasts longer.
Markers reward the matched comparison on all three points: impulse along neurones versus hormone in the blood; fast versus slower; short-lived versus longer-lasting.
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