GCSEScienceAQACombined Science: TrilogyBiologyRevision NotesHomeostasis & ResponseHormones: Maintaining Blood HomeostasisHuman Endocrine System

Human Endocrine System (AQA GCSE Combined Science: Trilogy: Biology): Revision Note

Exam code: 8464

Written by: Lára Marie McIvor

Reviewed by: Dr Natalie Lawrence

Updated on 3 September 2026

Endocrine system structure & function

The human endocrine system is composed of glands which secrete chemicals called hormones directly into the bloodstream
The blood carries the hormone around the body, and when it reaches a target cell/organ it produces an effect
Compared to the nervous system the effects of hormones are slower but they act for longer
Important structures in the endocrine system include the:
- pituitary gland: a ‘master gland’ making hormones such as FSH and LH
- pancreas: produces insulin which regulates the blood glucose level
- thyroid: produces thyroxine which controls metabolic rate and affects growth
- adrenal glands: produce adrenaline
- ovaries (females): produce oestrogen
- testes (males): produce testosterone

Diagram of endocrine system structures

Diagram of the human body showing the positions of major endocrine glands and examples of the hormones they produce. The pituitary gland is located at the base of the brain and is described as the ‘master gland’. The thyroid gland is located in the neck and produces thyroxine. The pancreas is located in the abdomen and produces insulin, which helps regulate blood glucose concentration; it also produces digestive enzymes including pancreatic amylase and lipase. The adrenal glands are located above the kidneys and produce adrenaline. The testes are shown in the male reproductive system and produce testosterone, the male sex hormone. An inset of the female reproductive system shows the ovaries, which produce oestrogen, a female sex hormone. — **Major endocrine glands produce hormones that are transported in the blood to regulate processes throughout the body**

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Examiner Tips and Tricks

Make sure you can recognise the structures listed in the diagram above in the exam and explain what they do.

Pituitary gland

The pituitary gland in the brain is a ‘master gland’ which secretes several hormones into the blood in response to body conditions
These hormones in turn act on other glands to stimulate other hormones to be released to bring about effects
- For example, in certain conditions, the pituitary gland makes and secretes thyroid-stimulating hormone (TSH) which stimulates the thyroid to release thyroxine

Diagram of pancreatic hormone release and target tissues

Alt text: Diagram showing how hormones are secreted into the blood and act only on specific target cells. Pancreatic gland cells produce and secrete hormone molecules, shown as green triangles, into a nearby blood capillary. The hormone is transported in the blood around the body. Cells surrounding the capillary have receptors on their cell membranes. Target cells have receptors with a complementary shape to the hormone, allowing the hormone to bind and produce a response. Non-target cells do not have the appropriate receptor, so the hormone does not bind to them. The liver and pancreas are shown as examples of organs involved in hormonal regulation. — **Hormones travel in the blood but only affect target cells with receptors complementary to that hormone**

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