2.2

• Hormones


  Chemical messengers released from a gland in response to a signal from the nervous system (or a change in the internal environment) and they travel to a target tissue in the blood stream
• Hormones


  • Each hormone is specific to its target tissue and therefore only acts on one organ/tissue
• Hormonal influence on puberty

  1. Hypothalamus secretes a releaser hormone

  2. Releaser hormone targets the pituitary gland

  3. Pituitary releases FSH and LH in females, FSH and ICSH in males

  4. Release of these hormones triggers the onset of sperm production in men and the menstrual cycle in women
• FSH (Follicle Stimulating Hormone)


  Stimulates sperm production in the seminiferous tubules of the testes
• ICSH (Interstitial Cell Stimulating Hormone)


  Stimulates the interstitial cells to produce testosterone
• Testosterone


  Promotes sperm production in the seminiferous tubules, activates seminal vesicles and prostate gland
• Negative Feedback Control of Testosterone

  1. High testosterone levels detected in the brain

  2. Inhibits the release of FSH and ICSH from the pituitary gland

  3. Prevents stimulation of interstitial cells and release of more testosterone

  4. Testosterone levels decrease back to normal

  5. Inhibition removed, pituitary can release FSH and ICSH again
• Negative Feedback Control


  A self-regulating mechanism where a change away from the optimum/set norm is detected by receptors that switch on a corrective mechanism to restore the condition back to normal
• Hormonal Control of the Menstrual Cycle

  1. Follicular Phase: Pituitary secretes FSH, stimulates follicle development and oestrogen production

  2. Oestrogen stimulates proliferation of endometrium and affects cervical mucus

  3. Peak oestrogen triggers LH surge from pituitary, which triggers ovulation

  4. Luteal Phase: Corpus luteum forms and secretes progesterone

  5. Progesterone further develops and vascularises the endometrium
• High levels of ovarian hormones (oestrogen and progesterone) in luteal phase


  Trigger an inhibitory effect on the pituitary gland, decreasing FSH and LH
• Lack of LH from pituitary


  Leads to degeneration of corpus luteum and drop in progesterone, causing menstruation
• If fertilisation occurs


  Corpus luteum does not degenerate, progesterone levels remain high