The Menstrual Cycle Flashcards
Which two cycles run side by side during the menstrual cycle?
Preparation of the gamete – ovarian cycle
Preparation of the endometrium – uterine cycle
What is the first phase of the ovarian cycle called?
Follicular Phase
What are the hormone levels and situation at the beginning of the menstrual cycle?
No ovarian hormone production. Early development of follicles begins. Low steroid and inhibin levels, little inhibition at the hypothalamus or anterior pituitary. Free from inhibin and steroid inhibition FSH levels begin to rise.
What does the first rise in FSH result in?
FSH binds to granulosa cells continuing follicular development, theca interna cells appear and so the follicle is now capable of oestrogen and inhibin secretion.
What is the role of oestrogen and inhibin in the follicular phase?
At first oestrogen negatively inhibits FSH but later follicular oestrogen reaches a concentration when it can exert positive feedback at the hypothalamus and anterior pituitary. It does this by increasing sensitivity of anterior pituitary to GnRH. This causes LH and FSH to rise – positive feedback. Follicular inhibin rises selectively inhibiting FSH production by anterior pituitary as we need to prevent recruitment of any further follicles
What does the rapid rise in oestrogen and inhibin cause?
Circulating oestrogen and inhibin rise rapidly, oestrogen production no longer dependant on FSH so there is a surge in LH production. Progesterone production begins because the granulosa cells have become responsive to LH.
What marks the start of the luteal phase?
Ovulation – meiosis I completes, and meiosis II starts and then pauses. Mature oocytes extruded through the capsule of the ovary.
What happens to the follicle after the egg leaves?
After ovulation, the follicle is luteinised. The follicle secretes oestrogen and progesterone in large quantities. Inhibin continues to be produced but LH is now supressed because of negative feedback of progesterone. Further gamete development suspended.
What does the corpus luteum do during the luteal phase?
Corpus luteum produces progesterone and oestrogen from androgens and produces inhibin. It regresses spontaneously after 14 days if there is no other luteinising signal i.e. hCG.
In the absence of a further rise in LH corpus luteum regresses. This causes a dramatic fall in gonadal hormones. Relieving negative feedback resetting the hormone back to the start of low concentrations of everything.
How is the luteal phase different if fertilisation occurs?
If fertilisation has occurred – syncytiotrophoblast produces human chorionic gonadotrophin which exerts a luteinising affect.
Corpus luteum supported by the placental hCG produces steroid hormones to support the pregnancy. Eventually the placenta is capable of production of sufficient quantities of steroid hormones to control the HPO axis throughout pregnancy.
What cause the period to occur?
The drop, in progesterone and oestrogen at the end of the cycle causes a spasm of the arterial supply of the endometrium causing it to become ischaemic and shed.
What are the name of the two uterine cycle phases?
Proliferative and secretory phases
What is the action of follicular stage oestrogen on the uterus?
Follicular stage Oestrogen – proliferation of the endometrium and formation of a thin alkaline cervical mucus, vaginal changes and changes in skin, hair and metabolism.
What is the action of follicular stage progesterone on the uterus?
Luteal stage progesterone – Inhibition of proliferative effects of oestrogen and stimulates a secretory/glandular form. A thick acid cervical mucus is formed, there are changes in mammary tissue and increased body temperature.
What is the normal length of the menstrual cycle?
Cycle duration – menstruation occurs on a monthly cycle throughout reproductive life unless interrupted by a pregnancy. Normal duration 21-35 days. Variations in cycle duration due to variation in the length of the follicular phase. Luteal phase strictly controlled 14 +/- 2 days.
