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Reproductive system > Lecture 8- The Menstrual Cycle > Flashcards

Lecture 8- The Menstrual Cycle Flashcards

1
Q

The Hypothalamic-Pituitary-Gonadal (HPG) Axis

A

The hypothalamus, anterior pituitary gland and gonads (ovaries) work together to regulate the menstrual cycle.

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2
Q

Gonadotropin releasing hormone (GnRH) from the hypothalamus stimulates

A

luteinising hormone (LH) and follicular stimulating hormone (FSH) release from the anterior pituitary gland.​

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3
Q

LH and FSH are gonadotropins that act primarily on the ovaries in the female reproductive tract: FSH binds to

A

FSH binds to granulosa cells to stimulate follicle growth, permit the conversion of androgens (from theca cells) to oestrogens and stimulate inhibin secretion

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4
Q

LH and FSH are gonadotropins that act primarily on the ovaries in the female reproductive tract: LH binds to

A

acts on theca cells to stimulate production and secretion of androgens

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5
Q

Moderate oestrogen levels exert a ………….feedback on the HPG axis

A

negative

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6
Q

High oestrogen levels (in the absence of progesterone (due to increased inhibin) ………..feedback on the HPG axis

A

positively

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7
Q

Oestrogen in the presence of progesterone exerts …………….feedback on the HPG axis

A

negative

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8
Q

Inhibin selectively inhibits …………at the anterior pituitar

A

FSH

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9
Q

summary of the feedback systems acting on the HPG axis

A
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10
Q

the menstrual cycle is

A

Menstrual cycle

  • 2 cycles happening in parallel- ovarian and uterine
    • Ovarian cycle- 2 phases
      • Pre ovulation- follicular phase
      • Post ovulation- luteal phase
    • Uterine cycle- 2 phases
      • Pre-ovulation
        • Period
        • Proliferative
      • Post-ovulation
        • secretory
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11
Q

average length of menstrual cycle

A
  • Average length =28 days
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12
Q
A
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13
Q

GnRH release in females

*

A
  • Female HPG axis is pulsatile
  • Persistent presence of GnRH would lead to desensitisation of its receptors on gonadotrophs
    • FSH and LH production cease
    • Gonadal steroid production ceases

Clinical importance

  • GnRH analogous e.g. Decapeptyl aka Triptorelin pamoate- used in treatment of endometriosis and infertility
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14
Q

the ovarian cycle involves the

A

follicular phase- pre-ovulatory

Luteal phase- post ovulatory

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15
Q

The follicular phase marks the

A

beginning of a new cycle as follicles (oocytes surrounded by stromal cells) begin to mature and prepare to release an oocyte.

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16
Q

At the start of a new cycle (menses) there is little

A

ovarian hormone production and the follicle begins to develop independently of gonadotropins or ovarian steroids.

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17
Q

Due to the low steroid and inhibin levels at the begining of the follicular phase….

A

there is little negative feedback at the HPG axis, resulting in an increase in FSH and LH levels. These stimulate follicle growth and oestrogen production.

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18
Q

how many follicles can contunue to maturity and compelte each menstrual cycle

A

Only one dominant follicle can continue to maturity and complete each menstrual cycle.

19
Q

As oestrogen levels rise,

A

negative feedback reduces FSH levels (inhibin), and only one follicle can survive, with the other follicles forming polar bodies.

20
Q

when is positive feedback at the HOG axis initiated

A

when oestrogen eventually becomes high enough

This…..increaseslevels of GnRH and gonadotropins.

21
Q

why do we only see a surge in LH when oestrogen levels initiate a positive feedback on the hypothalamus and pituitary

A

due to the increased follicular inhibin, selectively inhibiting FSH production at the anterior pituitary.

Granulosa cells become luteinised and express receptors for LH.

(LH SURGE= ovulation)

22
Q

Ovulation is in response to

A

to the LH surge , the follicle ruptures and the mature oocyte is assisted to the fallopian tube by fimbria. Here it remains viable for fertilisation for around 24 hours.

23
Q
A
24
Q

what happens to the empty follicle after ovulation

A

the follicle remains luteinised, secreting oestrogen and now also progesterone, reverting back to negative feedback on the HPG axis. This, together with inhibin (inhibits FSH) stalls the cycle in anticipation of fertilisation.

25
Q

luteal phase represents the

A

corpus luteum development and maintainence

26
Q

what is the corpus luteum and what does it produce

A

is the tissue in the ovary that forms at the site of a ruptured follicle following ovulation.

It produces:

  • oestrogens
  • progesterone
27
Q

why is the corpus luteum important

A

maintains conditions for fertilisation and implantation.

28
Q

At the end of the cycle, in the absence of fertilisation

A

the corpus luteum spontaneously regresses after 14 days.

There is a significant fall in hormones, relieving negative feedback, resetting the HPG axis ready to begin the cycle again.

29
Q

If fertilisation occurs, what stimulates (lutenises) the CL

A

the syncytiotrophoblast of the embryo produces human chorionic gonadotropin (HcG), exerting a luteinising effect, maintaining the corpus luteum. It is supported by placental HcG and it produces hormones to support the pregnancy. At around 4 months of gestation, the placenta is capable of production of sufficient steroid hormone to control the HPG axis.

30
Q

summary of the ovarian cycle

A
  1. initially low oestrogen, inhibin and progesterone will send negative feedback to the H and AP –> inhibitng release of LH
  2. as the follicle grows it will produce more and more oestrogen and inhibin (inhibits FSH) which will at a set point change the negative feedback to positive feedback
  3. causing a surge in LH
  4. LH surge casuses rupture of the ovum from the follicle
  5. the follicle will turn into a corpus luteum, which is stimulated by HcG and produces oestrogen, progesterone to help maintain conditions for fertilisation and implantation
31
Q

The uterine cycle

A
  • Pre-ovulation
    • Proliferative
  • Post-ovulation
    • secretory
32
Q

proliferative phase

A

Following menses, the proliferative phase runs alongside the follicular phase, preparing the reproductive tract for fertilisation and implantation.

33
Q

oestrogens role in the proliferative phase

A

initiates fallopian tube formation, thickening of the endometrium, increased growth and motility of the myometrium and production of a thin alkaline cervical mucus (to facilitate sperm transport).

34
Q

Secretory Phase

A

The secretory phase runs alongside the luteal phase.

35
Q

progesterone in the secretory phase

A

stimulates further thickening of the endometrium into a glandular secretory form, thickening of the myometrium, reduction of motility of the myometrium, thick acidic cervical mucus production (a hostile environment to prevent polyspermy), changes in mammary tissue and other metabolic changes.

  • endometrial thickness at maximum, very coiled glands, coiled arterioles
36
Q

Menses

A

Menses marks the beginning of a new menstrual cycle. It occurs in the absence of fertilisation once the corpus luteum has broken down and the internal lining of the uterus is shed.

37
Q

Menstrual bleeding usually lasts between

A
38
Q

Oestrogen

  • Highest in
A
  • Follicular phase
    • Thickening of endometrium
    • Increases fallopian tube function- cilia which waft oocyte along fallopian tube
    • Growth and motility of myometrium
    • Produces thin alkaline cervical mucus- for sperm
    • Vaginal changes
    • Changes skin, hair, metabolism
39
Q
  • Progesterone is Highest in
A
  • Luteal phase
    • Further thickening of endometrium (secretory)
    • Thickening of myometrium and reduction of motility- to stop implanted embryo from being expelled
    • Thick acidic cervical mucus
    • Development of breast tissue
    • Increased body temp
    • Metabolic changes
    • Electrolyte changes
40
Q
A
41
Q

Cycle length- what is normal

  • *
A
  • Normal duration 21-35 days
  • Variation is due to length of follicular phase
  • Luteal phase
42
Q

Disruption to cycle

A
  • Physiological factors
  • Pregnancy
  • Lactation
  • Emotional stress
  • Body weight
  • Infertility
43
Q
A

Reproductive system (28 decks)

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