Menstrual Cycle Flashcards
What are the 2 phases of the menstrual cycle?
- follicular phase
- luteal phase
When does the follicular phase occur?
- occurs from the start of menstruation to the moment of ovulation
- the length is variable, but it is 14 days in a 28 day cycle
the ovum is inside a follicle that is developing during this phase
When does the luteal phase occurs?
- this occurs from the moment of ovulation to the start of menstruation
- this is the final 14 days of the cycle
- the luteal phase is ALWAYS 14 days in length
the ovum has exited the ovary during ovulation and the remnants are the corpus luteum
When does ovulation always occur?
14 days before the end of the menstrual cycle
e.g. day 14 of a 28 day cycle
or day 16 of a 30 day cycle
What are follicles?
- from puberty, the ovaries contain a finite number of cells that have the potential to develop into eggs
- these cells are oocytes
- granulosa cells surround the oocytes to form follicles
What are the 4 stages of follicle development in the ovaries?
- primordial follicles
- primary follicles
- secondary follicles
- antral follicles / Graafian follicles
How do follicles initially mature within the ovary?
- the process of primordial follicles maturing into primary + secondary follicles is occurring ALL THE TIME
- this is independent of the menstrual cycle
- secondary follicles develop the receptors for FSH
- further development after the secondary follicle stage requires FSH
How do the secondary follicles develop further?
- at the start of the menstrual cycle, FSH stimulates further development of the secondary follicles
- the granulosa cells surrounding them secrete increasing amounts of oestradiol (oestrogen)
What is the effect of oestradiol secretion by the granulosa cells?
- it has a negative feedback effect on the pituitary gland
- this reduces the levels of FSH + LH
- rising oestrogen thins the cervical mucus, allowing sperm to penetrate the cervix around the time of ovulation
What happens to only one of the developing follicles during the menstrual cycle?
- one follicle develops further than the others and becomes the dominant follicle
- an LH surge prior to ovulation causes the dominant follicle to release an ovum from the ovary
- this is ovulation
What is meant by the LH surge?
- just before ovulation, there is a dip in oestrogen levels
- this causes a spike in LH
- this causes the dominant follicle to reach the surface of the ovary and release the ovum
What happens to the follicle that released the ovum after ovulation?
- it collapses + becomes the corpus luteum
- this secretes high levels of progesterone
- it also secretes a small amount of oestrogen
this is the start of the luteal phase
What are the roles of progesterone secreted by the corpus luteum?
- it maintains the endometrial lining
- it causes the cervical mucus to become thick and no longer penetratable
What is the fate of the corpus luteum if fertilisation occurs?
- the syncitiotrophoblast of the embryo secretes human chorionic gonadotrophin (hCG)
- hCG maintains the corpus luteum
- without hCG, the corpus luteum degenerates
What is the fate of the corpus luteum if fertilisation does NOT occur?
- in the absence of hCG, the corpus luteum degenerates
- the production of oestrogen + progesterone ceases
- this causes the endometrium to break down and menstruation to occur
In addition to degeneration of the CL, what else facilitates menstruation?
- release of prostaglandins by the stromal cells of the endometrium
- prostaglandins encourage the endometrium to break down + uterus to contract
On what day of the menstrual cycle does menstruation start?
- menstruation starts on day 1 of the cycle
- the negative feedback from oestrogen / progesterone on the pituitary gland ceases
- this allows the levels of FSH + LH to begin to rise and the cycle to restart
What is involved in menstruation?
- the superficial + middle layers of the endometrium separate from the basal layer
- tissue is broken down inside the uterus and released via the cervix / vagina
- the release of this substance lasts between 1-8 days
What is involved in the hypothalmo-pituitary-ovarian axis?
- the hypothalamus releases gonadotrophin-releasing-hormone
- this stimulates the release of FSH + LH by the anterior pituitary gland
- oestrogen released by the granulosa cells suppresses their release
What factors can affect the secretion of GnRH?
- bereavement
- anxiety
- time zone
- working day / night shifts
- exercise
- weight loss / gain
What is the overall function of FSH?
- stimulates follicular development
- this promotes the production of estradiol from granulosa cells
What is the overall function of LH?
- triggers the release of an egg from the dominant follicle
- promotes development of the corpus luteum + production of progesterone
What is the effect of the COCP on this cycle?
- it contains both estradiol + progestogen
- this inhibits GnRH and LH / FSH
- this prevents ovulation
- the endometrium remains thin and the cervical mucus remains thick
progestagen = synthetic progesterone
