7 - Menstrual Cycle Flashcards
What are the two cycles that make up the menstraul cycle and what is the length of a normal cycle?
- Ovarian Cycle: provide environment for oogenesis in ovary
- Uterine Cycle: prepare uterus to recieve fertilised oocyte
21-35 days
What is the difference in the negative feedback system on the HPG between males and females?
- Testosterone has inhibitory affect on hypothalamus and anterior pituitary
- Oestrogen can be positive or negative feedback depending on where in the cycle
Why is GnRH being released in a pulsatile manner important in the reproductive system?
If there was a continous production it’s receptors in the pituitary would become desensitised so may lead to infertility
What is endometriosis and how can it be treated?
What?
- Ectopic endometrial tissue leading to abdominal pain
Treatment?
- Give continuous GnRH to stop desensitise receptors
- OC pill
How can you treat precocious puberty?
Give constant GnRH to densensitise receptors
What is the role of FSH and LH in females?
FSH: allows folicles to develop in ovary at start of cycle. follicles produce oestrogen and inhibin (which is negative feedback on FSH)
LH: LH surge drives ovulation
What is the first stage of the menstrual cycle?
Follicular phase
- No inhibition from steroids or inhibin so FSH levels rise
- Number of granulosa cells increase due to FSH and causes development of theca interna/externa
- Follicle produces oestrogen so oestrogen levels rise and exert negative feedback on anterior pituitary
- Follicles form into Graafian follicle and oestrogen levels rise further exerting positive feeback on HPG
- Inhibin levels rise stopping FSH so only LH rise
- This stage is variable
What are the different stages of follicular development in the ovary?
When is the dominant follicle chosen in the follicular cycle and how is it chosen?
- Around 7th day
- Decrease in FSH due to the inhibin secretion
- Increase in LH due to the rising oestrogen having positive feedback
What causes ovulation - the release of the mature follicle?
- Inhibin and oestrogen rise rapidly and no longer dependent on FSH
- Progesterone production begins and granulosa cells responsive to LH, modulating GnRH pulse generator
- LH surge
What happens to the oocyte during ovulation?
- Meiosis I completes and II starts
- Oocyte extruded through the capsule
What happens to the levels of sex hormones immediately after ovulation?
- Follicle luteinised and starts to secrete oestrogen and progesterone in large quantities
- Inhibin continued to be produced
- LH suppressed due to negative feedback of progesterone
- Waiting phase where gamete development suspended
What is the second stage of the ovarian cycle called?
- Luteal Phase
- Corpus Luteum has absolute lifespan of 14 days
- Oestrogen, progesterone and inhibin all secreted from theca and granulosa
- If LH stays high corpus luteum regresses
What are the two stages of the uterine cycle?
- Proliferative phase
- Secretory phase
What occurs in the proliferative phase of the uterine cycle?
- Endometrium thickens in response to oestrogen from the ovary
- Simple straight glands that start to become coiled glands as the functional layer doubles
- All occurs at start of cycle
What occurs in the secretory phase of the menstrual cycle?
- Glands in endometrium become secretory under influence of progesterone
- At the end the glands lose their structure and endometrium becomes ready to shed
- This occurs after ovulation
What happens at the end of the menstrual cycle that leads to menstruation?
- No further rise in LH after 14 days so corpus luteum regresses
- Fall in gonadal hormones as regresses
- Negative feedback relieved
- Starts again
What happens to the menstrual cycle if fertilisation and implantation occurs?
- Syncytiotrophoblast secrete hCG
- hCG has same effect as LH so maintains C.Luteum making progesterone
- Placenta takes over steroid hormone production at end of 1st trimester
What is the histiological structure of the uterus?
Functional layer made up of zona compacta and zona spongiosa
Apart from changes in the uterus, what other changes in the body occur during the follicular phase?
Effects of oestrogen intended to promote fertilisation
Apart from changes in the uterus, what other changes in the body occur during the luteal phase?
Effects of progesterone are intended to sustain a viable pregnancy
What are some factors that can affect the menstrual cycle and it’s duration/presence?
- Pregnancy
- Lactation
- Emotional stress
- Low body weight
