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3002 > 79 Hormonal control the of the menstrual cycle > Flashcards

79 Hormonal control the of the menstrual cycle Flashcards

1
Q

What are the main ovarian events during the menstrual cycle?

A

FOLLICULAR PHASE (days 1-14)

  1. Multiple follicles develop
  2. On day 7 one follicle becomes dominant
  3. Dominant follicle matures
  4. Ovulation occurs (day 14)

LUTEAL PHASE (days 14-28)

  1. Corpus luteum functions
  2. Corpus luteum degenerates
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2
Q

Name the 2 anterior pituitary gonadotropins

A

LH

FSH

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3
Q

Name 2 gonadal sex hormones

A

Oestrogen

Progesterone

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4
Q

FSH hormonal pattern?

A

Increases in early part of follicular phase, then steadily decreases throughout
remainder of cycle EXCEPT small midcycle peak

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5
Q

LH hormonal pattern?

A

Constant during most of follicular phase, then large midcycle increase (LH surge) peaking ~18h before ovulation. Then rapid decrease with further slow decline during the luteal phase

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6
Q

Oestrogen hormonal pattern?

A

Low and stable for 1st week, increases rapidly in 2nd weeks, starts to decline before LH peak. Then second increase due to corpus luteum in last few days of cycle

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7
Q

Progesterone hormonal pattern?

A

Low level due to ovary release during follicular phase with small increase just before ovulation. Soon after ovulation, large increase due to CL release, then similar pattern to oestrogen

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8
Q

Inhibin hormonal pattern?

A

Similar pattern to oestrogen ie increases in late follicular phase, remains high during luteal phase, decreases as corpus luteum degenerates

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9
Q

Feedback effects of ovarian hormones?

A
  1. Oestrogen, in low plasma concentrations, causes the anterior pituitary to secrete less FSH & LH in response to GnRH and also may inhibit the hypothalamic neurons that secrete GnRH.
    RESULT: -ve feedback inhibition of FSH & LH secretion during the early and middle follicular phase
  2. Inhibin acts on the pituitary to inhibit the secretion of FSH
    RESULT: -ve feedback inhibition of FSH secretion throughout the cycle
  3. Oestrogen, when increasing dramatically, causes anterior pituitary cells to secrete more LH + FSH in response to GnRH. Oestrogen can also stimulate the hypothalamic neurons that secrete GnRH.
    RESULT: +ve feedback stimulation of the LH surge, which triggers ovulation
  4. High plasma concentrations of progesterone, in the presence of oestrogen, inhibit the hypothalamic neurons that secrete GnRH.
    RESULT: -ve feedback inhibition of FSH + LH secretion and prevention of LH surges during the luteal phase and pregnancy
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10
Q

Role of Follicle Stimulating Hormone (FSH)?

A

During 1st week of follicular phase it stimulates the growth of medium sized follicles

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11
Q

Which cells express FSH receptors?

A
  • Granulosa cells of the ovary express FSH receptors during the follicular phase of the menstrual cycle
  • These cells are homologous to the Sertoli cells of the testis
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12
Q

Role of Luteinising Hormone (LH)?

A

During the secretory phase it stimulates steroid hormone synthesis by the corpus luteum

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13
Q

What stimulates the LH peak 12hrs before ovulation?

A

Increasing rate of secretion of oestrodiol-17beta

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14
Q

Role of LH and FSH in control of oestrogen synthesis during the early and middle follicular phases?

A
  • LH stimulate theca cells of ovarian follicle
  • FSH stimulate granulosa cells of the ovarian follicle
  • Theca cells: Synthesise androgens (androstenedione)
  • Granulosa cells: Convert androgens (diffused from theca cells through BM) —> oestrogen. Also secretes inhibin
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15
Q

What events leads to the LH surge?

A
  1. Dominant follicle release large amounts of oestrogen
  2. Oestrogen stimulates:
    - Hypothalamus to secrete GnRH
    - Ant pituitary to secrete LH
  3. Increased plasma LH triggers ovulation and formation of CL (produces progesterone and oestrogen)
  4. LH action are mediated by the granulosa cells
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16
Q

What is the secretion regulation of oestrogen?

A

• Interrelated feedback loops
• Mid-cyme shift form -ve to +ve feedback:
- Caused by upregulation of receptors (e.g. GnRH from hypothalamus in ant pituitary) when oestrogen levels are increased
- Results in LH and FSH surge prior to ovulation

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17
Q

Effects of LH surge on ovarian function:

  1. Meisosis and cytoplasm
  2. Antrum/blood
  3. Hormone release
  4. Follicular-ovarian membranes
  5. CL
A
  1. The 1° oocyte completes its 1st meiotic division and undergoes cytoplasmic changes that prepare the ovum for implantation should fertilisation occur. These LH effects on the oocyte are mediated by messengers released from the granulosa cells in response to LH
  2. Antrum size (fluid volume) and blood flow to the follicle increase markedly
  3. The granulosa cells begin releasing progesterone and decreasing the release of oestrogen, which accounts for the midcycle decrease in plasma oestrogen concentration and the small rise in plasma progesterone just before ovulation
  4. Enzymes and prostaglandins, synthesized by the granulosa cells, breakdown the follicular-ovarian membranes. These weakened membranes rupture, allowing the oocyte and its surrounding granulosa cells to be carried into the surface of the ovary
  5. The remaining granulosa cells of the ruptured follicle (along with the theca cells of that follicle) are transformed into the corpus luteum, which begins to release progesterone and oestrogen
18
Q

7 functions of granulosa cells?

A
  1. Nourish oocyte
  2. Secrete chemical messengers that influence the oocyte and theca
    cells
  3. Secrete antral fluid
  4. Site of action for oestrogen and FSH in the control of the follicle development during early and middle follicular phases
  5. Express aromatase, which converts androgen (from theca cells) to oestrogen
  6. Secrete inhibin, which inhibits FSH secretion via an action on the pituitary
  7. Site of action for LH induction of changes in the oocyte and follicle culminating in ovulation and formation of CL
19
Q

What happens to LH and FSH in luteal phase?

A

Suppression of LH and FSH in luteal phase

20
Q

What happens if there is no implantation in the luteal phase?

A
  • hCG does no appear in blood
  • CL dies
  • Progesterone and oestrogen decrease
  • Menstruation occurs and next MC begins
21
Q

Enough oestrogen from ovary –> __ surge induced —> ovulation –> when __ degenerates —> decrease ________ secretion —> __ + __increase enough for new follicle growth

A

Enough oestrogen from ovary –> LH surge induced —> ovulation –> when CL degenerates —> decrease (oestrogen/progesterone) secretion —> FSH + LH increase enough for new follicle growth

22
Q

What does the surge in LH result in? Cause?

A
  • Triggers ovulation (resumption of meiosis)

* Caused by rapid rise in plasma oestrogen

23
Q

What happens if progesterone remains high?

A
  • Levels of LH and FSH will be suppressed and ovulation will not occur
  • Occurs in pregnancy
24
Q

How is ovulation prevented in pregnancy?

A
  • Progesterone remains high - leaves of LH and FSH will be suppressed so ovulation won’t occur
  • Human chorionic gonadotrophin produced by placenta maintains CL which continues to secrete progesterone
25
Q

What hormone is exploited therapeutically in the oral contraceptive pill?

A
  • Oestrogen

* Suppresses LH and FSH and prevents ovulation

26
Q

What does oestrogen stimulate to grow?

A
  1. Ovary and follicles (local effects)
  2. Smooth muscle and proliferation of epithelial linings of reproductive tract
  3. External genitalia growth, particularly during puberty
  4. Breast growth, particularly ducts and fat deposition during puberty
  5. Bone growth and ultimate cessation of bone growth (closure of epiphyseal plates); protects against does not have anabolic effect on skeletal muscle
27
Q

Effect of oestrogen on Fallopian tubes?

A

Increases contractions and ciliary activity

28
Q

Effect of oestrogen on uterus?

A
  • Increases myometrial contractions and responsiveness to oxytocin
  • Stimulates secretion of abundant, watery cervical mucus
  • Prepares endometrium for progesterone’s actions by inducing progesterone receptors
29
Q

Effect of oestrogen on vagina?

A

Increases layering of epithelial cells

30
Q

Effect of oestrogen on females body configuration during puberty?

A
  • Narrow shoulder
  • Broad hips
  • Female fat distribution (deposition on hips and breasts)
31
Q

Effect of oestrogen on skin glands?

A

Stimulates fluid secretion from lipid (sebum)-producing skin glands (sebaceous glands)
• (“anti-acne” effect opposing the acne-producing effect of androgen)

32
Q

Effect of oestrogen on prolactin?

A

Stimulates prolactin secretion but inhibits prolactin’s milk-inducing action on the breasts

33
Q

What does oestrogen protect against?

A
  • Osteoporosis

* Atherosclerosis - effects n plasma cholesterol, blood vessels and blood clotting

34
Q

Effect of oestrogen on vascular system?

A

Vascular effects - deficiency produces “hot flashes”

35
Q

Effects of progesterone?

A
  1. Converts the oestrogen-primed endometrium to an actively secreting tissue suitable for implantation of any embryo
  2. Induces thick, sticky cervical mucus
  3. Decreases contractions of fallopian tubes and endometrium
  4. Decreases proliferation of vaginal epithelial cells
  5. Stimulates breast growth particularly glandular tissue
  6. Inhibits milk-inducing effects of prolactin
  7. Has feedback effects on hypothalamus and anterior pituitary
  8. Increases body temperature
36
Q

Summary of oestrogen

A
  • Produces by ovary
  • Increases motility of the uterine tube
  • Causes proliferation of the endometrium
  • Systemic effects - development of secondary sexual characteristcs
37
Q

Summary of progesterone

A
  • Produced by ovary
  • Causes secretory activity in the endometrium
  • Systemic effects - viscous cervical mucus
38
Q

What occurs in the early and mid follicular phases?

A
  • FSH stimulates the granulosa cells to proliferate and secrete oestrogen
  • LH stimulates theca cells to proliferate and produce androgens that the granulosa cells use to make oestrogen:
  1. During this time, oestrogen exerts -ve feedback on the anterior pituitary to inhibit the secretion of the gonadotropins. Also probably inhibits the secretion of GnRH by the hypothalamus
  2. Inhibin preferentially inhibits FSH secretion
39
Q

What occurs in the late follicular phase?

A

Plasma oestrogen increases to elicit a surge of LH which then causes, via the granulosa cells, completion of the egg’s 1st meiotic division and cytoplasmic maturation, ovulation, and formation of CL

40
Q

What occurs during the luteal phase?

A
  • Under the influence of small amounts of LH, CL secretes progesterone and oestrogen
  • Regression of the CL results in cessation of the secretion of these hormones

• Secretion of GnRH and the gonadotropins is inhibited during the luteal phase by the combination of progesterone, oestrogen and inhibin

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