(a) Hormonal influence on puberty

• The pituitary gland is stimulated to release

• • follicle stimulating hormone (FSH),
  • luteinising hormone (LH)
  • or interstitial cell stimulating hormone (ICSH)

• by a releaser hormone produced in the hypothalamus.
• This triggers the onset of puberty.

(b) Hormonal control of sperm production

• FSH promotes sperm production and ICSH stimulates the production of testosterone.
• Testosterone also stimulates sperm production and activates the prostate gland and seminal vesicles.
• Negative feedback control of testosterone is achieved by FSH and ICSH.
• When testosterone concentration becomes high, it is detected by the pituitary gland, which then lowers its production of FSH and ICSH.

(c) Hormonal control of the menstrual cycle

• The menstrual cycle takes approximately 28 days with the first day of menstruation regarded as day one of the cycle.

The follicular phase

• FSH stimulates the development of a follicle and the production of oestrogen by the follicle in the follicular phase.
• Oestrogen stimulates proliferation of the endometrium preparing it for implantation, and affects the consistency of cervical mucus making it more easily penetrated by sperm.
• Peak levels of oestrogen stimulate a surge in the secretion of LH.
• This surge in LH triggers ovulation.
• Ovulation is the release of an egg (ovum) from a follicle in the ovary.
• It usually occurs around the mid-point of the menstrual cycle.

The luteal phase

• In the luteal phase the follicle develops into a corpus luteum which secretes progesterone.
• Progesterone promotes further development and vascularisation of the endometrium preparing it for implantation if fertilisation occurs.
• The negative feedback effect of the ovarian hormones on the pituitary gland and the secretion of FSH and LH 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.
• If fertilisation does occur the corpus luteum does not degenerate and progesterone levels remain high.