11.1 Principles of Hormonal Control

A free GCSE Biology lesson for AQA (8461) from OBA School: the endocrine system, the main glands and how hormones compare with nerves. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Describe the endocrine system as glands that secrete hormones directly into the blood
• Name and locate the pituitary, thyroid, pancreas, adrenal glands, ovaries and testes
• Explain why the pituitary gland is called the “master gland”
• Compare hormonal (endocrine) control with nervous control

Key words

• Endocrine system: The system of glands that secrete hormones directly into the bloodstream.
• Gland: An organ that makes and releases (secretes) a useful substance, such as a hormone.
• Hormone: A chemical messenger made by a gland and carried in the blood to a target organ.
• Target organ: The organ a hormone acts on. Its cells respond to that hormone; other cells do not.
• Pituitary gland: A pea-sized gland at the base of the brain. It is the “master gland”.
• Coordination: Making different parts of the body work together in response to changes.

What is the endocrine system?

Your body has two systems that coordinate what it does: the nervous system and the endocrine system. The endocrine system is made of glands. Each gland secretes chemicals called hormones directly into the bloodstream.

The blood carries the hormone all around the body, but it only has an effect on its target organ. The cells of the target organ respond to the hormone, for example by changing what they make or how fast they work.

Key fact: Gland → secretes hormone into the blood → blood carries it → target organ → response.

Worked example: exam tip

Question: “Describe how a hormone reaches its target organ.” (2 marks)
Good answer: The hormone is secreted directly into the blood by a gland (1). It is carried in the bloodstream to the target organ (1).
Do not say the hormone travels “along nerves” or “through tubes”.

Answer: Always mention “blood”.

The main endocrine glands

You need to know where six glands are found in the body and one job of each.

• Pituitary; Where it is Base of the brain; Hormone(s) FSH, LH, TSH, ADH, growth hormone; Main effect Controls other glands; growth; water balance
• Thyroid; Where it is Front of the neck; Hormone(s) Thyroxine; Main effect Controls the basal metabolic rate
• Pancreas; Where it is Behind the stomach; Hormone(s) Insulin, glucagon; Main effect Controls blood glucose concentration
• Adrenal glands; Where it is On top of each kidney; Hormone(s) Adrenaline; Main effect Prepares the body for “fight or flight”
• Ovaries; Where it is Lower abdomen (female); Hormone(s) Oestrogen, progesterone; Main effect Menstrual cycle; female sex characteristics
• Testes; Where it is Scrotum (male); Hormone(s) Testosterone; Main effect Sperm production; male sex characteristics

The pituitary: the master gland

The pituitary gland secretes several hormones into the blood. Some of these act on other glands and stimulate them to release their own hormones. Because it controls so many other glands, the pituitary is called the master gland.

• TSH (thyroid stimulating hormone); Target gland Thyroid; What the target gland then does Releases thyroxine
• FSH (follicle stimulating hormone); Target gland Ovaries; What the target gland then does An egg matures; the ovaries release oestrogen
• LH (luteinising hormone); Target gland Ovaries; What the target gland then does An egg is released (ovulation)

Worked example: a chain of hormones

Explain how the pituitary gland affects the metabolic rate.
The pituitary releases TSH into the blood. TSH travels to the thyroid gland. The thyroid releases thyroxine, which raises the basal metabolic rate.

Answer: pituitary → TSH → thyroid → thyroxine → metabolic rate

Hormones compared with nerves

Both systems detect changes and bring about responses, but they work in different ways.

• Type of signal; Nervous system Electrical impulses (and chemicals at synapses); Endocrine system Chemical (hormones)
• How it travels; Nervous system Along neurones; Endocrine system In the blood
• Speed of response; Nervous system Very fast; Endocrine system Slower
• How long it lasts; Nervous system Short; Endocrine system Longer
• Where it acts; Nervous system A very precise area (one muscle or gland); Endocrine system Target organs, wherever they are in the body

Worked example: choosing the system

Which system controls (a) pulling your hand off a hot pan, (b) the growth of a teenager?
(a) Needs a very fast, short response in one place → nervous.
(b) A slow change that lasts for years and affects many organs → hormonal.

Answer: (a) nervous (b) hormonal

Tip: Hormonal effects are slower but last longer than nervous effects.

Common mistakes

• Saying hormones travel along nerves. Hormones are carried in the blood.
• Saying a hormone affects every cell. It only affects the cells of its target organ(s).
• Placing the pituitary in the neck. It is at the base of the brain; the thyroid is in the neck.
• Mixing up the adrenal glands and the kidneys. The adrenal glands sit on top of the kidneys.
• Writing that hormonal responses are faster than nervous ones. They are slower but last longer.

Revision questions

Try these, then check your answers below each one.

Question 1. How do endocrine glands release their hormones? (Choose from: Directly into the bloodstream, Into tubes that lead to the gut, Along nerve cells, Onto the surface of the skin.)

Answer: Directly into the bloodstream

Working: Endocrine glands secrete hormones directly into the blood, which carries them to their target organs.

Question 2. Which gland is known as the “master gland”? (Choose from: Thyroid, Pituitary, Pancreas, Adrenal.)

Answer: Pituitary

Working: The pituitary secretes hormones such as TSH and FSH that stimulate other glands, so it is called the master gland.

Question 3. True or false? Hormonal responses are usually slower than nervous responses but last for longer.

Answer: True

Working: True. Hormones travel in the blood, so they act more slowly, but their effects last longer.

Related lessons

• Previous lesson: 10.7 Required Practicals: The Human Nervous System
• Next lesson: 11.2 The Control of Blood Glucose Levels
• In this chapter: 11.3 Treating Diabetes
• In this chapter: 11.4 The Role of Negative Feedback
• In this chapter: 11.5 Human Reproduction

Continue in the full course

This lesson is section 11.1 (AGCBH1101) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.