IGCSE Coordinated Science: Hormones

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7.2 Hormones

1 Define a hormone as a chemical substance, produced by a gland, carried by the blood,which alters the activity of one or more specific target organs and is then destroyed by the liver.

Hormones are chemical substances which are produced by a gland, and their function is to alter the activity of one or more specific target organs. The hormone is then destroyed by the liver.

2 State the role of the hormone adrenaline in the chemical control of metabolic activity, including increasing the blood glucose concentration and pulse rate.

Adrenaline has an effect on blood glucose concentrations. In heavy exercise, adrenaline will signal the liver to commence gluconeogenesis. This will use the lactic acid which muscles are producing as a byproduct of exercise and start converting it to glucose. Liver breaks down some of the stored glycogen –> extra glucose is released into the blood

Adrenaline increases pulse rate. This is because in a “fight or flight (life or death)” situation, both these activities need oxygen and energy.


The brain realizes this and subsequently sends signals to the adrenal glands which secrete adrenaline into the bloodstream. The heart rate increases as the body girds itself for what it is about to do: fight or run. The blood vessels and air passages dilate, allowing more blood to the muscles and oxygen to the lungs.

3 Give examples of situations in which adrenaline secretion increases.

I gave one just now. Your adrenaline secretion increases during a “flight or fight” situation. This is a situation where you either sit down to face the situation (aka, your GF :D), or just run away. However, whichever option you opt for requires oxygen and energy. The brain realizes this and subsequently sends signals to the adrenal glands which adrenaline into the bloodstream. This gives you more energy to either fight or flight.

P4 Compare nervous and hormonal control systems.

Nervous: reaction time is fast.
Hormonal: slow
N: message sent through neurons
H. message sent by hormones
N message sent as an electrical impulse
H. message sent as an organic message
N. responsible for nervous co-ordination
H. responsible for chemical co-ordination
N. enables body to respond to external environment
H. enables body to respond to internal environment.

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N message sent as an electrical impulse

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3 Responses to IGCSE Coordinated Science: Hormones

  1. R. says:

    this will us? that doesn’t make sense.. *number 2*

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