hormonal control of reproduction

• Hormones released by the pituitary gland at puberty are:

  • Follicle stimulating hormones (FSH)
  • Luteinising hormone (LH)
  • Interstitial cell stimulating (ICSH)
• A releaser hormone produced in the hypothalamus stimulates the release of hormones by the pituitary gland to trigger the onset of puberty.
• FSH promotes sperm production and ICSH stimulates the production of testosterone. Testosterone promotes sperm production and activates the prostate gland and seminal vesicles.
• Negative feedback controls the production of testosterone.

  1. Low levels of testosterone fails to inhibit the pituitary gland.
  2. An increased concentration of ICSH is released by the pituitary gland.
  3. Interstitial cells produce testosterone.
• The menstrual cycle takes approximately twenty-eight days and the first day of menstruation is regarded as day one.
• The menstrual cycle is split into three distinctive phases:

  • The follicular phase
  • The luteal phase
  • The menstrual phase
• 1. FSH stimulates the development of the follicle and the production of oestrogen by the follicle, in the follicular phase.
• 2.

  • Oestrogen stimulates the expansion of the endometrium (lining of the uterus) preparing it for implantation and affects the consistency of cervical mucus.
  • The mucus becomes thinner and waterier in consistency making it more easily penetrated by sperm.
• 3.

  Peak levels of oestrogen stimulate the surge in the secretion of LH. The surge in LH triggers ovulation.
• Ovulation is the release of (ovum) from a follicle in the ovary. It usually occurs around the mid-point of the menstrual cycle.
• 4. Luteal phase:

  The follicle develops into a corpus luteum which secretes progesterone.
• 5. Progesterone promotes further development and vascularisation of the endometrium preparing it for implantation if fertilisation occurs.
• 6. Progesterone and oestrogen inhibit further secretion of FSH and LH to prevent further follicles from developing. The lack of LH leads to degeneration of the corpus luteum with a subsequent drop in progesterone levels leading to menstruation.
• Progesterone levels remain high and the corpus luteum does not regenerate if fertilisation occurs.
• The decrease in progesterone concentration causes the endometrium to break down and menstruation begins.