The Menstrual Cycle Flashcards
What does the ovarian cycle involve?
Preparation of the gamete – ovarian cycle - follicular and luteal phases
What does the uterine cycle involve?
Preparation of the endometrium – uterine cycle - proliferative and secretory phases
Describe and explain the hormone levels at the beginning of a 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 2 important things does the rising FSH levels at the beginning of the menstrual cycle 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. .
After the intitial rise in FSH what happens?
Need to prevent recruitment of any further follicles. Follicular oestrogen now at a concentration when it can exert positive feedback at the hypothalamus and the anterior pituitary – increases sensitivity of anterior pituitary to GnRH. This causes LH to rise. Follicular inhibin rises selectively inhibiting FSH production by anterior pituitary.
How does the cycle prepare for ovulation?
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. Modulation of the GnRH pulse generator occurs because of the progesterone (becomes more rapid just before ovulation).
What happens to begin 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 after ovulation?
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. Waiting phase established .
What hormones does the corpus luteum produce and when will it regress?
Luteal phase – corpus luteum produces progesterone and oestrogen from androgens and produces inhibin. It regresses spontaneous 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.
What happens 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 causes the endometrium shed?
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 main actions of oestrogen in the follicular stage?
Follicular stage Oestrogen – fallopian tube function, thickening of endometrium, growth and motility of myometrium, thin alkaline cervical mucus, vaginal changes and changes in skin, hair and metabolism.
What are the main actions of progesterone in the luteal phase?
Luteal stage progesterone – further thickening of endometrium into secretory/glandular form, thickening of myometrium but reduction of motility, thick acid cervical mucus, changes in mammary tissue, increased body temperature, metabolic changes and electrolyte changes.
What is a normal cycle duration?
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.
What can affect the menstrual cycle?
Factors affecting the menstrual cycle
Pregnancy, lactation, emotional stress and low body weight.
