The menstrul cycle Flashcards
What is the menstrual cycle?
A cycle controlled by hormones that causes typically regular bleeding (periods).
What hormones are involved in the menstrual cycle?
• Follicle stimulating hormone (FSH)
• Luteinising hormone (LH)
• Oestrogen
• Progesterone
How long does the menstrual cycle last?
About 28 days, although many people have longer or shorter cycles.
They can also be irregular.
What is the follicular phase?
The first 14 days of the cycle, ending in ovulation.
What is the luteal phase?
The last 14 days of the cycle.
What is ovulation?
This involved the release of an egg (ovum) from one of the ovaries.
What is oestrogen?
This is released by the ovaries.
It is a steroid sex hormone that actors on tissues with oestrogen receptors.
It stimulates the development of breast tissue, the vulva, vagina and uterus.
It also assists in the formation and maintenance of the endometrium (the womb lining), as it stimulates the blood vessels in the uterus to develope the endometrium.
What does a rise in oestrogen lower the level of?
FSH and LH.
What is day one of the menstrual cycle?
The first day of the period.
What happens during the follicular phase?
• This starts with day 1, the onset of menstruation (a period).
• This occurs when an egg cell has not been fertilised during the previous cycle.
• During the menstrual flow phase, progesterone levels are low, allowing the release of FSH and LH from the pituitary gland.
• FSH stimulates the growth of a follicle.
• The growing follicles produce oestrogen, causing the concentration of oestrogen to increase.
• Just before day 14, the concentration of oestrogen reaches a high enough level to cause a surge in LH from the pituitary gland.
• The LH surge causes ovulation and the egg is released from the follicle on day 14.
What does oestrogen inhibit and stimulate during the follicular phase?
When the growing follicles produce oestrogen, the oestrogen:
• inhibits the production of FSH which ensures that (usually) only one egg matures each cycle. This is an example of negative feedback.
• stimulates the growth and repair of the lining of the uterus, preparing it to accept a fertilised egg
What happens during the luteal phase?
• Once the egg cell has been released, the follicle becomes the corpus luteum.
• The corpus luteum releases progesterone.
• The concentration of progesterone in the blood rises, inhibiting the release of LH and FSH by the pituitary gland (an example of negative feedback).
• Progesterone maintains the lining of the uterus so it is ready to accept a fertilised egg.
• If fertilisation does not occur, the corpus luteum breaks down and the concentration of progesterone and oestrogen decreases.
• The fall in progesterone and oestrogen levels triggers menstruation, on average around day 28 of the cycle.
• The cycle then begins from day 1 again.
What happens if fertilisation does occur?
The placenta takes over the production of progesterone.
This maintains the lining of the uterus during pregnancy so menstruation doesn’t occur.
