Normal Menstrual Cycle And Ovulation Flashcards
What is menarche?
This is the first menstrual bleed in a female. It is usually the last evidence of poverty. It is usually the last evidence of puberty.
What is the menstrual cycle?
This is marked by the shedding of the endometrium which lines the uterus.
What is the overview of menstrual cycle?
- At the end of menstruation, the endometrium thickens again and the whole cycle begins again.
- Alongside the changes in the uterus are changes in the ovaries which lead on to ovulation- comprised of ovarian and uterine cycles.
- The average duration of the cycle is 28 days.
- The cycle is controlled by the HPO axis.
What is the endocrine control of menstrual cycle?
- Hypothalamus controls the cycle.
- Starting from the puberty, the hypothalamus releases GnRH (gonadotrophin-releasing hormone). GnRH is released in a pulsatile manner approximately every 90 minutes.
- This acts on the anterior pituitary stimulating it to release FSH and LH.
- FSH encourages follicular development and along with LH stimulates the granulosa cells of the dominant follicle to produce oestrogen.
- There is a surge of LH that occurs halfway through the cycle and this causes ovulation.
- The empty follicle after releasing an egg develops into the corpus luteum.
- The corpus luteum secretes progesterone which makes the endometrial glands secretory.
What is the follicular phase?
o LH and FSH stimulate the development of several follicles but only one matures fully.
o Oestrogen is produced from the granulosa cells of the developing follicle.
o As follicles develop, there is negative feedback which reduces FSH and LH secretion which leads to the selection of only the most sensitive follicle only, with others becoming atretic.
o The granulosa cells also produce inhibin which stops multiple follicles from maturing at the same time by negative feedback suppressing FSH secretion.
What is ovulation?
o As oestrogen levels continue to rise, the negative feedback to the pituitary instead becomes a positive feedback loop leading to a surge of LH.
o The follicle, which has grown significantly, protrudes from the ovarian cortex, ruptures and releases the oocyte. Ovulation occurs within 36hrs of the LH surge.
What is the luteal phase?
o The follicle that is left after the egg has been erupted is infiltrated by capillaries and fibroblasts.
o It undergoes luteinisation where the granulosa cells in the follicle hypertrophy and fat accumulates within them giving it a yellow colour. This forms the corpus luteum.
o The corpus luteum produces a high level of progesterone and a secondary rise in oestrogen. In this phase of the cycle, FSH and LH are at extremely low levels until the corpus luteum degenerates fully.
How many parts is comprised in the uterine cycle?
Menstruation.
Proliferative phase.
Secretory phase.
What happens during menstruation?
o The first day of menstruation is the beginning of the menstrual cycle.
o The endometrium sheds as there is no support from progesterone.
o The superficial layer of the endometrium contains arterioles which go into spasm following the fall of progesterone.
o This causes ischaemic necrosis and shedding of the superficial layer of the endometrium.
o The muscular layer of the uterus, the myometrium may also contract causing pain.
What is the proliferative phase?
• Proliferative phase: Day 5-13:
o Oestrogen secretion from the maturing follicle causes the glands in the endometrium to enlarge and elongate and the stromal cells proliferate leading to a thickening of the endometrium.
o As oestrogen continues to rise, it reaches a peak and has a positive effect on the hypothalamus and pituitary causing to LH to rise sharply.
o Ovulation occurs 36hrs after the LH surge.
o NB: this phase occurs during the follicular phase of the ovarian cycle
What is the secretory phase?
• Secretory phase: Day 14-28:
o After ovulation, progesterone from the corpus luteum make the endometrium ‘secretory’. The stromal cells enlarge, the glands swell, and the blood supply increases.
o This makes the endometrium ready for the implantation of a fertilized egg. If no fertilization occurs, then menstruation occurs.
o NB: this phase correlates with the luteal phase of the ovarian cycle.
o Ovulation is confirmed by regular menstrual cycle and by mid-luteal progesterone measurement.
What is used to measure irregular/absent periods?
o GnRH pulses – not measured routinely in clinical practice
o FSH / LH:
Low – hypothalamic/ pituitary pathology
Normal – disrupted folliculogenesis, but oocytes present
High – low number /absence of oocytes
o Oestradiol – produces by granulosa cells -if present and if stimulated
o AMH – produced by pre-antral and small antral follicles. Excellent indicator of oocyte reserve
What are the causes of ovulatory dysfunction?
o Hypothalamic (FSH, LH and oestradiol Low) GnRH deficiency Weight loss etc o Pituitary (FSH, LH and oestradiol Low) Hyperprolactinaemia Other pituitary dysfunctions o Ovarian PCOS (FSH normal, LH raised and oestradiol normal) Premature ovarian failure (FSH and LH high, oestradiol low)
Which hormones are used to measure ovarian reserves?
o AMH is used to test ovarian reserve as it can be measured at any time of the cycle, there’s little inter-cycle variability and it is the best marker.
o FSH can also be used to measure ovarian reserve. Greater than 9 means that there is a reduced reserve.
What is the definition of infertility in women?
The diminished ability of a couple to conceive a child. This may result from a definable cause (e.g., ovulatory, tubal, or sperm problem), or may be unexplained failure to conceive over a 2-year period.
