Menstrual Cycle Flashcards

1
Q

What are the 2 phases of the menstrual cycle?

A
  • follicular phase
  • luteal phase
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2
Q

When does the follicular phase occur?

A
  • 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

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3
Q

When does the luteal phase occurs?

A
  • 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

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4
Q

When does ovulation always occur?

A

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

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5
Q

What are follicles?

A
  • 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
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6
Q

What are the 4 stages of follicle development in the ovaries?

A
  • primordial follicles
  • primary follicles
  • secondary follicles
  • antral follicles / Graafian follicles
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7
Q

How do follicles initially mature within the ovary?

A
  • 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
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8
Q

How do the secondary follicles develop further?

A
  • 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)
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9
Q

What is the effect of oestradiol secretion by the granulosa cells?

A
  • 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
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10
Q

What happens to only one of the developing follicles during the menstrual cycle?

A
  • 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
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11
Q

What is meant by the LH surge?

A
  • 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
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12
Q

What happens to the follicle that released the ovum after ovulation?

A
  • 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

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13
Q

What are the roles of progesterone secreted by the corpus luteum?

A
  • it maintains the endometrial lining
  • it causes the cervical mucus to become thick and no longer penetratable
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14
Q

What is the fate of the corpus luteum if fertilisation occurs?

A
  • the syncitiotrophoblast of the embryo secretes human chorionic gonadotrophin (hCG)
  • hCG maintains the corpus luteum
  • without hCG, the corpus luteum degenerates
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15
Q

What is the fate of the corpus luteum if fertilisation does NOT occur?

A
  • 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
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16
Q

In addition to degeneration of the CL, what else facilitates menstruation?

A
  • release of prostaglandins by the stromal cells of the endometrium
  • prostaglandins encourage the endometrium to break down + uterus to contract
17
Q

On what day of the menstrual cycle does menstruation start?

A
  • 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
18
Q

What is involved in menstruation?

A
  • 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
19
Q

What is involved in the hypothalmo-pituitary-ovarian axis?

A
  • 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
20
Q

What factors can affect the secretion of GnRH?

A
  • bereavement
  • anxiety
  • time zone
  • working day / night shifts
  • exercise
  • weight loss / gain
21
Q

What is the overall function of FSH?

A
  • stimulates follicular development
  • this promotes the production of estradiol from granulosa cells
22
Q

What is the overall function of LH?

A
  • triggers the release of an egg from the dominant follicle
  • promotes development of the corpus luteum + production of progesterone
23
Q

What is the effect of the COCP on this cycle?

A
  • 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