Biology · Hormonal Coordination in Humans
Hormones and the Endocrine System
Hormones are chemical messengers that coordinate the body more slowly than nerves, but with longer-lasting effects. This lesson covers the principles of hormonal coordination and control, where the main endocrine glands are in the body, and how hormonal control compares with nervous control.
Learning Objectives
- 1Describe the principles of hormonal coordination and control by the human endocrine system.
- 2Identify the positions of the pituitary gland, pancreas, thyroid, adrenal gland, ovary and testes on a diagram of the human body.
- 3Compare nervous control and hormonal control.
Retrieval practice
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1
What carries substances around the body?
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The blood.
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2
What is a gland?
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An organ that makes and releases a chemical, such as a hormone.
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3
What is the nervous system made of?
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The brain, the spinal cord and the nerves.
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4
What is an effector?
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A muscle or gland that carries out a response.
A second communication system
The nervous system is very fast, but it is not the only way the body coordinates itself. The endocrine system uses chemical messengers called hormones, which are carried in the blood. They take longer to arrive, but they can control processes that go on for hours, days or even years, such as growth, reproduction and the use of energy.
How hormones work
The endocrine system is made of glands that release hormones directly into the blood.
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Hormone
A chemical messenger made in an endocrine gland and carried in the blood.
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Endocrine gland
A gland that releases its hormone straight into the blood, not along a tube.
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Transport
The blood carries the hormone to every part of the body.
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Target organs
A hormone only affects its target organs, which have receptors that fit that hormone. Other cells ignore it.
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The effect
The target organ responds, for example by releasing another chemical, growing or releasing energy.
The main endocrine glands
Each gland releases different hormones with different jobs.
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Pituitary gland
The master gland, in the brain. It releases several hormones into the blood in response to body conditions. These hormones act on other glands, which then release other hormones. It also releases growth hormone, FSH, LH and ADH.
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Thyroid gland
In the neck. It releases thyroxine, which controls the rate of metabolism.
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Pancreas
Below the stomach. It releases insulin and glucagon, which control blood glucose.
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Adrenal glands
Above the kidneys. They release adrenaline, which prepares the body for action.
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Ovaries
In females. They release oestrogen and progesterone.
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Testes
In males. They release testosterone.
The endocrine glands
The endocrine glands release hormones into the blood.
Nervous control and hormonal control
Nervous system
- Electrical impulses along neurones
- Very fast response
- Short-lived effect
- Acts on a precise place, such as one muscle
Endocrine system
- Chemical hormones in the blood
- Slower response
- Longer-lasting effect
- Acts on target organs that can be anywhere in the body
The big idea
The endocrine system uses hormones released by glands into the blood, which act on target organs more slowly than nerves but for longer.
The endocrine system
The endocrine system
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Hormones
- chemical messengers carried in the blood
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Target organs
- have receptors that fit the hormone
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Main glands
- pituitary
- thyroid
- pancreas
- adrenals
- ovaries
- testes
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Compared with nerves
- slower
- longer-lasting
Summary and exam focus
- Hormones are chemical messengers released by endocrine glands into the blood.
- A hormone only affects its target organs, which have the right receptors.
- The pituitary is the master gland, and the other glands are the thyroid, pancreas, adrenals, ovaries and testes.
- Hormonal control is slower than nervous control and lasts longer.
Exam focus
Compare nervous control with hormonal control. (4 marks) (4 marks)
Use comparison words such as faster, slower, longer, shorter. Cover how the message travels, the speed, how long the effect lasts and where it acts.
Key terms
The words this lesson expects you to use. Each one is linked from the first place it appears above.
- Hormone
- A chemical messenger carried in the blood.
- Endocrine gland
- A gland that releases hormones into the blood.
- Target organ
- An organ with receptors that respond to a particular hormone.
- Pituitary gland
- The master gland that releases hormones controlling other glands.
- Thyroid gland
- The gland in the neck that releases thyroxine.
- Adrenal gland
- A gland above the kidney that releases adrenaline.
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