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This system comprises of chemicals released from glands, directly into the blood stream that bring about changes. Hormonal reactions are more constant and longer lasting than nervous.

Location of Glands

the location of the major hormonal glands in the body and which hormones they produce

Oestrogen and Testosterone

Whilst you were in the womb, oestrogen and testosterone were getting to work on either making you a boy or girl - so that a baby is born with sex organs. But around 12 years later ...

During puberty the sex hormones (oestrogen for females, testosterone for males) are produced in larger amounts, causing further changes called secondary sexual characteristics. These are:

  • Breasts develop
  • Pubic hair grows
  • Hips widen
  • Mensturation begins
  • Body hair grows
  • Voice deepens
  • Muscles grow
  • Produce sperm

  • The last two points for each hormone talk about stimulating growth of gametes (sex cells). This process is relatively simple in males, but for females it is continuous, must prepare the uterus for fertilisation and involves a combination of different hormones.

    Some women have poor fertility and so find it difficult to conceive a baby. To increase the ripening of the eggs, drugs containing FHS can be given. Follicle Stimulating Hormone can also be given to induce the release of several eggs at a time so they can be harvested for in vitro fertilisation (more on this in genetics).


    The adrenal glands sit above the kidneys and produce the hormone adrenaline to prepare the body for physical activity, this is know as the 'fight-or-flight' response as it prepares you to stand up to or run away from a lethal situation, and this had an evolutionary benefit.

    The rate and depth of breathing increases, this means there is more oxygen available to the muscles. Glycogen in the liver is converted into glucose to allow for increased respiration (opposite of what insulin does). Vasoconstriction (blood vessels get thinner) to skin and gut, and vasodilation to muscles so that more blood gets to them, this also will make you look pale and give butterflies in the tummy.