Hormones as chemical messengers, the comparison of nervous and hormonal coordination, the role of the pituitary as the master gland, and how hormones travel in the blood to target organs.

What this dot point is asking

AQA wants you to describe hormones as chemical messengers carried in the blood, compare hormonal and nervous coordination, and explain the role of the pituitary gland as the master gland of the endocrine system.

Hormones as chemical messengers

Because hormones travel in the blood, they reach the whole body, but only the target organ has the right receptors to respond, which is why a hormone only affects certain organs. For example, insulin from the pancreas acts mainly on the liver and muscles.

Comparing nervous and hormonal coordination

Both systems coordinate the body, but they work in different ways:

This is why nerves are used for things that need a quick, short response, such as a reflex to remove a hand from danger, while hormones control longer-term, widespread processes such as growth, the menstrual cycle and the control of blood glucose. The two systems often work together: for example, both the nervous system (shivering) and a hormone (adrenaline) can be involved in responding to cold or stress.

The pituitary gland

For example, the pituitary releases TSH, which stimulates the thyroid to release thyroxine, and FSH and LH, which act on the ovaries and testes. This makes the pituitary the central controller of much of the endocrine system.

A common exam skill is to read information about a hormone and decide whether the response described fits the nervous or the hormonal system. The clues are timescale and spread: if the response is almost instant and very localised (such as catching a ball), it is nervous; if it builds up slowly and affects much of the body over hours, days or years (such as the changes of puberty or the control of blood glucose after a meal), it is hormonal. AQA often gives an unfamiliar example and expects you to apply these rules rather than recall a fact.

It is also worth remembering that the two systems are not rivals. They frequently act together: when you are frightened, the nervous system produces the immediate jump, while the hormone adrenaline produces the longer-lasting raised heart rate and alertness. Understanding that the body uses the right tool for the right timescale is the underlying idea AQA is testing.

Try this

Q1. Define a hormone. [2 marks]

• Cue. A chemical messenger made by a gland and carried in the blood to a target organ.

Q2. State two differences between nervous and hormonal responses. [2 marks]

• Cue. Nervous: fast and short-lived; hormonal: slower and longer lasting.