2.2 Hormonal control
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Hypothalamus
releaser hormone released from here triggers puberty.
Proliferation of the endometrium is stimulated by
Oestrogen
High levels of oestrogen stimulate
surge in the release of LH.
stimulates the increased production of FSH by the pituitary.
Oestrogen
What triggers the start of menstruation?
Falling levels of progesterone
Degeneration of the corpus luteum is caused by low levels of
LH
FSH on males
Seminiferous tubules start to produce sperm. FSH promotes sperm production
How is puberty initiated
The hypothalamus produces a releaser hormone.
Follicle 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
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.
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.
Negative feedback effect of the ovarian hormones
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.
Menstrual cycle
The menstrual cycle takes approximately 28 days with the first day of menstruation regarded as day one of the cycle.