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Y4 Obstetrics and Gynaecology > Menstrual cycle & sex steroid axis > Flashcards

Menstrual cycle & sex steroid axis Flashcards

1
Q

List the key reproductive hormones

A
  • GnRH
  • LH
  • FSH
  • Oestrogen
  • Progesterone
  • Testosterone
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2
Q

Where is GnRH secreted from and what does it stimulate the secretion of ?

A

It is released from the hypothalamus and stimulates the release of FSH & LH from the anterior pituitary

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3
Q

Describe the manner in which GnRH is released

A
  • It is released in a pulsatile manner
  • In males GnRH is secreted in pulses at a constant frequency
  • Whereas in females the frequency of the pulses varies during the menstrual cycle, pulses every 1-2 hrs during the early follicular phase, decreasing in frequency late follicular phase and decrease frequency to every 4 hours during the luteal phase
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4
Q

What do high and low frequency GnRH pulses stimulate ?

A
  • High-frequency GnRH pulses stimulate LH
  • Low-frequency pulses are required for FSH release
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5
Q

What effect does oestrogen and progesterone have on GnRH pulses ?

A
  • Oestrogen concentrations above a certain threshold will increase GnRH pulsatility driving the release of LH
  • Increase in progesterone concentrations reduces the frequency of GnRH pulses
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6
Q

The onset of pubertal maturation is associated with what?

A

A steady acceleration in GnRH pulsatility (peak at night; In boys, this diurnal rhythm results in peak testosterone in the early morning leading to erections)

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7
Q

GnRH pulsatility is regulated by oestrogen and progesterone however GnRH producing neurons do not contain a receptor for these hormones ==> what neurones do oestrogen and progesterone indirectly act on to regulate GnRH pulsatility ?

A

Kisseptin neurones

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8
Q

What is the function of FSH & LH in males ?

A
  • FSH - causes the testes to produce sperm (spermatogenesis)
  • LH - causes the testes to secrete testosterone
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9
Q

What is the function of FSH & LH in females ?

A
  • FSH - stimulates ovarian follicular development (oogenesis), thickens the endometrium & it causes the ovary to secrete oestrogen
  • LH - LH peak causes ovulation and stimulates corpus luteum development and production of progesterone by the corpus luteum. Also thickens the endometrium
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10
Q

What is the menstrual cycle ?

A

It is a complex series of physiological changes occuring in a women on a monthly basis resulting in prodicution of an ovum & thickening of the endometrium to allow for implantation if fertilisation should occur

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11
Q

How long does one entire menstrual cycle last ?

A
  • 28days
  • Note - normal range is 28-35
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12
Q

When does the first day of the menstrual cycle begin ?

A

On the first day of menstruation (when they see blood)

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13
Q

How long does bleeding typically last ?

A

3-8 days

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14
Q

When does ovulation occur in the menstrual cycle ?

A

On day 14

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15
Q

What controls the menstrual cycle ?

A
  • The hypothalamus - it regulates the hormones released from the anterior pituitary
  • It releases gonadotropin releasing hormone (GnRH) which stimualtes the anterior pituitary gland to release FSH & LH
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16
Q

Describe the stages of development of the ovum

A
  1. FSH & LH travel to the female ovaries
  2. In each ovary there are many follicles (primordial), each month only some of the follicles begin to mature due to the rise in FSH levels at the start of the cycle
  3. While these follicles are maturing they produce oestrogen
  4. Only one of the developing follicles will reach full maturity (Graafian follicle) & ovulate
  5. During the first 10 days of the cycle oestrogen has a -ve feedback on the pituitary gland where it inhibits LH but after 10 days its levels have increased where the opposite effect happens and it & GnRH stimulate LH secretion causing a LH surge triggering ovulation
  6. During ovulation the oocyte is released
  7. The oocyte turns into the corpus luteum (under the influence of LH which then starts to slowly degrade but it will also secrete hormones - oestrogen, progesterone & inhibin
  8. If no fertilisation (like in a normal menstrual cycle) occurs, the corpus luteum degrenerates and the hormones it secretes decrease, eventually allowing GnRH levels to rise
  9. GnRH levels increase due to not being inhibited by progesterone ==> new cycle occurs
  10. Also at the same time as the new cycle initiating because of the decreased oestrogen & progesterone levels it means the endothelial linning will no longer be maintained and thus will shed off (known as the period)
17
Q

What are the 2 phases of the menstrual cycle ?

A
  • Follicular phase: days 0-14
  • Luteal phase: days 14-28
18
Q

What is the effect of oestrogen concentrations on FSH & LH and how does this affect their levels during the start of the menstrual cycle?

A
  • Low concentrations of oestrogen will inhibit LH secretion and will stimulate FSH secretion ==> LH levels do not change at the start due to oestrogen inhibiting and GnRH stimulating cancelling eachother out. Whilst FSH levels initially increase & then decrease as oestrogen levels increase as cycle progresses
  • High concentrations of oestrogen will stimulate LH secretion
19
Q

Why does the concentration of oestrogen increase from start of menstrual cycle to ovulation (14 days) ?

A

Because as the follicles in the ovaries mature they produce more oestrogen

20
Q

What happens to oestrogen levels following ovulation ?

A

They will decrease slightly

21
Q

What happens to inhibin concentrations during the menstrual cycle ?

A

It was not present prior to ovulation, afterwards it begins to increase due to the corpus luteum

22
Q

What happens to progesterone levels during the menstrual cycle ?

A

Prior to ovulation they were low, afterwards they increase during the luteal phase

23
Q

Describe the stages of the menstrual cycle

A
  1. Initially at the start of the menstrual cycle there is a steady increase in GnRH, which should cause an increase in FSH &LH, but instead a increse then decrease of FSH & steady level of LH is seen (due to effects of oestrogen)
  2. After 10 days the increase in GnRH & oestrogen (now high enough to stimulate LH) both stimulate LH secretion. Resulting in a massive spike in LH levels.
  3. The massive spike in LH levels triggers ovulation og Graafian follicle
  4. FSH also has a slight spike due to side effect of the massive LH surge
  5. After ovulation LH, FSH & GnRH levels all drop due to the action of progesterone & inhibin
24
Q

What is the effect of inhibin during the menstrual cycle ?

A

Produced by the corpus luteum it inhibits FSH stimulation because during the luteal phase we do not want anymore maturation of follicles in the ovaries ==> as the corpus luteum develops, inhibin secretion suppresses FSH secretion (-ve feedback)

25
Q

What are the overall effects of oestrogen on the body (not just talking about menstrual cycle)?

A
  • At low conc. it inhibits LH secretion, at high concs. it stimulates LH secretion
  • High estrogen concentration inhibits secretion of FSH and prolactin (-ve feedback)
  • It stimulates bone & muscle growth
  • It stimulates endometrial thickening (endometrial glands & stroma) (occurs during the follicular phase)
  • Maintains female secondary characterisitics & maintains glands (e.g. breast)
  • Reduce vaginal pH through increase in lactic acid production
  • Decrease viscosity of cervical mucus to facilitate sperm penetration
26
Q

What are the overally effects of progesterone in the body (not just talking about the menstrual cycle) ?

A
  • Its main effect is stimulating endometrial thickening (oestrogen also does this)
  • It has a -ve feedback effect on the pituitary where it inhibits the secretion of LH
  • Responsible for infertile thick mucus (prevent sperm transport and help prevent infection)
  • Relaxes the myometrium (smooth muscle). Functional progesterone withdrawal thought to regulate parturition (birth)
  • Has thermogenic effect (increases basal body temperature)
27
Q

What do decreasing FSH levels cause ?

A

Atresia of all developing follicles except the dominant one

28
Q

What happens during the luteal phase ?

A
  • Progesterone induced glandular secretory activity
  • Deciualisation (endometrium changes to structure called decidua, important role in promoting placenta formation)
  • Decidualised endometrial lining is shed if implantation does not occur i.e. period
29
Q

Go over this overview of the phases of the menstrual cycle and the hormones secreted

A

Y4 Obstetrics and Gynaecology (63 decks)

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