Hormones

  • Hormones are chemical messengers.

    • Hormones are produced in structures called glands.

    • Hormones are then released into the bloodstream.

  • Hormones act on target cells.

    • Hormones stimulate a change in the behaviour of these cells.

  • Hormones and their glands are collectively referred to as the endocrine system.

    • Once they have been used, hormones are recycled in the liver.

  • Adrenaline stimulates the ‘fight or flight’ response.

  • Adrenaline has a number of effects:

  1. Adrenaline causes the heart rate to increase.

    1. Adrenaline binds to receptors on cardiac muscle cells.

    2. Adrenaline causes the heart muscle to contract more frequently.

  2. Adrenaline causes the ventilation rate to increase.

    1. The ventilation rate is the number of breaths a person takes per minute.

    2. Increasing the ventilation rate allows more oxygen (O2) to reach cells for respiration.

  3. Adrenaline increases the blood flow to muscles.

  • Increasing the blood flow delivers the O2 to muscles for respiration.

  • This increases amount of energy that can be supplied to the muscles.

  • Adrenaline is secreted by the adrenal glands.

    • The adrenal glands are found just above the kidneys.

  • Insulin lowers the concentration of glucose in the bloodstream.

  • Insulin signals the liver to convert glucose into the storage molecule glycogen.

    • This causes the concentration of glucose in the blood to drop.

  • Insulin is secreted by the pancreas.

    • Insulin is secreted by a type of cell called β cells.

  • An inability to secrete insulin leads to Type I diabetes.

    • Type I diabetics are most commonly treated with regular injections of insulin.

  • Testosterone stimulates secondary sexual characteristics in males:

  1. Testosterone causes the voice to deepen.

    1. Testosterone is linked with the enlargement of the larynx and the stretching of the vocal cords.

  2. Testosterone stimulates muscle development.

  3. Testosterone stimulates the production of body hair.

    1. Body hair will grow on the face, under the armpits and in the pubic region.

  • There is a spike in testosterone production at puberty.

    • In boys, puberty begins at around age 12.

  • Testosterone is secreted from the testes.

  • Oestrogen stimulates secondary sexual characteristics in females:

  1. Oestrogen causes breasts to develop.

  2. Oestrogen stimulates the production of body hair.

    1. Body hair will grow under the armpits and in the pubic region.

  3. A surge in oestrogen stimulates the start of menstruation.

  • There is a spike in oestrogen production at puberty.

    • In girls, puberty begins at around age 11.

  • Oestrogen is secreted from the ovaries.

  • Progesterone maintains the lining of the uterus during pregnancy.

  • Progesterone also creates a cushioned environment for the egg to implant in.

  • Progesterone is also used as a contraceptive.

    • The progesterone-only pill is a very common form of birth control.

  • Progesterone is secreted from the ovaries.