Hormones and the endocrine system — Edexcel GCSE Biology
Where hormones are made and how they travel, plus adrenalin and thyroxine (Higher tier).
Revision notes
3 short notes, in the order of the specification. Each one in short:
Hormones are chemical messengers made in endocrine glands and released straight into the blood. The blood plasma carries them around the body, but each hormone affects only its target organs. The glands include the pituitary gland, thyroid gland, pancreas, adrenal glands, ovaries and testes. Hormones travel in the blood, not along nerves.
Adrenalin and fight or flight
Higher tierAdrenalin is a hormone produced by the adrenal glands that prepares the body for fight or flight. It increases heart rate, blood pressure and blood flow to the muscles, so the muscles get more oxygen and glucose for respiration. It also raises the blood sugar level by stimulating the liver to change glycogen into glucose.
Thyroxine and negative feedback
Higher tierThyroxine is a hormone made by the thyroid gland that controls metabolic rate, the rate of the chemical reactions in the body. Its level is kept steady by negative feedback. A low level stimulates the hypothalamus to produce TRH, which makes the pituitary gland release TSH, and TSH makes the thyroid produce thyroxine. A normal level inhibits TRH and TSH.
Exam questions
4 exam-style questions (11 marks), each with its mark scheme.
Answer the questionsFlashcards
14 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of animal coordination, control and homeostasis on one page, so you can see where this subtopic fits.
Open the mind mapPrint it
Free PDFs to print or save.
Quick check questions
How are hormones transported from endocrine glands to target organs?
Show answer
In the blood (plasma).
Which gland produces insulin?
Show answer
The pancreas.
Name the four effects of adrenalin. (Higher)
Show answer
Increased heart rate, increased blood pressure, increased blood flow to the muscles, and raised blood sugar level.
Which hormone does the pituitary release to make the thyroid produce thyroxine? (Higher)
Show answer
TSH.
Frequently asked questions
Why are hormones called chemical messengers?
Hormones are called chemical messengers because they are chemicals that carry a signal from one part of the body to another. They are made in endocrine glands and released straight into the blood, which carries them around the whole body in the plasma. Each hormone only causes a response in its target organs.
What does the pituitary gland do?
Higher tier The pituitary gland is an endocrine gland at the base of the brain that releases hormones that control other glands and organs. It releases FSH and LH, which act on the ovaries in the menstrual cycle, and TSH, which acts on the thyroid gland and makes it produce thyroxine.
What does adrenalin do to the body?
Higher tier Adrenalin prepares the body for fight or flight. It increases heart rate and blood pressure, so blood is pumped to the organs faster, and increases blood flow to the muscles, giving them more oxygen and glucose for respiration. It also stimulates the liver to change glycogen into glucose, which raises the blood sugar level.
How does thyroxine regulate metabolism?
Higher tier Thyroxine from the thyroid gland controls metabolic rate, the rate of the chemical reactions in the body. Its level is kept steady by negative feedback. When thyroxine is low, the hypothalamus produces TRH, which makes the pituitary gland release TSH, and TSH stimulates the thyroid. When the level is normal, thyroxine inhibits TRH and TSH.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026