⚡ Nervous system
Uses electrical impulses along neurones. The effects are fast and last for a short time. A reflex is a good example.
Hormonal Coordination in Humans » The Endocrine System
What you'll learn this session
Study time: 30 minutes
AQA spec: 4.5.3.1
- What the endocrine system is and what hormones are
- How hormones travel and how this compares with the nervous system
- Why the pituitary gland is called the master gland
- Where the main glands are in the human body
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Unlock This CourseA second control system
You have already met the nervous system, which sends fast electrical impulses along neurones. Your body has a second system for coordination and control. It uses chemical messages instead of electrical ones. This is the endocrine system.
The endocrine system is made up of glands. A gland is an organ that makes and releases a useful chemical. The glands of the endocrine system release their chemicals directly into the blood. These chemical messengers are called hormones.
Key terms:
- Endocrine system: the group of glands that secrete hormones directly into the bloodstream.
- Gland: an organ that secretes (releases) a useful chemical.
- Hormone: a chemical messenger secreted by a gland directly into the blood.
- Target organ: the organ where a hormone produces its effect.
- Pituitary gland: the gland in the brain that is called the 'master gland'.
How hormones work
A hormone does its job in three steps:
- A gland secretes the hormone directly into the bloodstream.
- The blood carries the hormone around the body.
- The hormone reaches its target organ, where it produces an effect.
The blood carries the hormone to many parts of the body, but the hormone only has its effect on its target organ.
Think of it like the post
The blood is like the delivery network. The hormone is the letter. It passes many houses, but it only has an effect at the address it is meant for: the target organ.
Endocrine system compared with the nervous system
Both systems coordinate what your body does, but they work in different ways. Compared with the nervous system, the effects of hormones are slower, but they act for longer.
🧪 Endocrine system
Uses hormones carried in the blood. The effects are slower, because the hormone has to be carried in the blood, but they act for longer.
A hormone has to be released and carried in the blood before it works. That is why it takes longer than a nerve impulse. Once it arrives, it keeps working for longer, so the body uses hormones for jobs that need to carry on for a long time.
The pituitary gland: the master gland
The pituitary gland is found in the brain. It is called a 'master gland' because it secretes several hormones into the blood in response to body conditions. These hormones in turn act on other glands. They stimulate those glands to release other hormones, and these bring about effects in the body.
So the pituitary works in a chain:
- The pituitary gland responds to body conditions and secretes hormones into the blood.
- These hormones travel in the blood to other glands.
- The other glands are stimulated to release their own hormones.
- Those hormones bring about effects in the body.
Master gland means 'in charge of other glands'
The pituitary is called the master gland because its hormones act on other glands. It does not do all the work itself.
Where are the glands?
You need to be able to identify the position of six glands on a diagram of the human body.
🧠 Pituitary gland
In the brain, at its base.
🌟 Thyroid
In the neck, in front of the windpipe (trachea).
🔶 Adrenal glands
One on top of each kidney.
🍳 Pancreas
In the upper abdomen, just below the stomach.
🌸 Ovaries
Two, in the lower abdomen of a female, one on each side.
🔵 Testes
Two, in the scrotum of a male, hanging below the body.
A good way to remember the order is to work down the body: head (pituitary), neck (thyroid), above the kidneys (adrenals), below the stomach (pancreas), then the lower body (ovaries or testes).
You will learn what the individual hormones do in later lessons, starting with Controlling Blood Glucose. For now you only need to know how the system works and where each gland is.
Common mistakes
Saying that hormones travel along neurones. They do not: hormones travel in the blood. Another mistake is writing that hormones act more quickly than nerves. Compared with the nervous system, hormone effects are slower but act for longer. Finally, do not say that a hormone has an effect on every organ. It produces its effect at its target organ.
Exam-style question
(a) Describe how a hormone gets from the gland that makes it to its target organ. [2 marks]
(b) A student says, 'Hormones work faster than nerves.' Explain why this is not correct. [2 marks]
(c) Explain why the pituitary gland is called the 'master gland'. [2 marks]
Model answer
(a) The gland secretes the hormone directly into the blood (1). The blood carries the hormone to the target organ, where it produces an effect (1).
(b) The effects of hormones are slower than those of the nervous system (1). They are carried in the blood, but they act for longer (1).
(c) The pituitary gland secretes several hormones into the blood (1). These hormones act on other glands and stimulate them to release other hormones (1).
Exam tip
When you compare hormones with nerves, use both words: slower and longer. Writing only one of them will not get both marks.