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(LUSUMA) COPY Reproductive System > S4) The Menstrual Cycle > Flashcards

S4) The Menstrual Cycle Flashcards

1
Q

Group the menstrual cycle into 3 general stages

A
  • Preparation – ovarian & uterine cycle
  • Ovulation – release of gamete
  • Waiting – maintaining endometrium until fertilisation occurs
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2
Q

Identify 2 types of hormones which control the menstrual cycle

A
  • Gonadotrophins
  • Ovarian steroids
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3
Q

Where do gonadotrophins act?

A

Gonadotrophins act on the ovary

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4
Q

What two actions do ovarian steroids do?

A
  • Act on tissues of the reproductive tract
  • Act to control the cycle
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5
Q

In the HPO axis, what substance is produced by the hypothalamus?

A

GnRH

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6
Q

In the HPO axis, what does GnRH do?

A

Acts on anterior pituitary to release gonadotrophins:

  • FSH
  • LH
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7
Q

In the HPO axis, what do gonadotrophins do?

A
  • Promoting follicular development
  • Promote production of ovarian hormones
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8
Q

Identify two types of ovarian hormones

A
  • Steroid hormones
  • Inhibin
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9
Q

How is the HPO axis controlled?

A
  • Controlled by effects of gonadal hormones
  • Negative and positive feedback control
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10
Q

Why is the pulsatile release of GnRH important?

A
  • Intermittent GnRH receptor is required for fertility
  • If GnRH receptors are exposed continuously to GnRH, they become desensitised and gonadotrophin production stops
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11
Q

What are the two stages in the ovarian cycle?

A
  • Follicular phase
  • Luteal phase
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12
Q

Describe the layout and actions of the HPO axis

A
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13
Q

What is the main event occuring at the start of the menstrual cycle?

A

Early development of follicles begins

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14
Q

Describe the hormone levels at the start of the menstrual cycle

A
  • No ovarian hormone production
  • Low steroid and inhibin levels
  • FSH levels rising
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15
Q

Describe the amount inhibition observed at the start of the menstrual cycle

A

Free from inhibition as there is little inhibition at the hypothalamus or anterior pituitary

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16
Q

Describe the effects of FSH on the developing follicles

A

FSH binds to granulosa cells:

  • Follicular development continues
  • Theca interna appears
  • Follicle now secretes oestrogen & inhibin
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17
Q

What two things need to occur in the mid follicular phase?

A
  • Nominate a dominant follicle
  • Prevent recruitment of any further follicles
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18
Q

Explain how FSH is inhibited by the developing ovarian follicle

A
  • [Follicular oestrogen] now exerts positive feedback on the hypothalamus and anterior pituitary
  • Selective inhibition of FSH occurs as only [LH] rises
  • [Follicular inhibin] rises
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19
Q

What 4 events occur in preparation for ovulation?

A

⇒ [Oestradiol and inhibin] rise rapidly

⇒ Oestradiol production independent of FSH

⇒ Surge in LH production

⇒ Modulation of GnRH pulse generator

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20
Q

What causes the surge in LH?

A
  • High [oestradiol] enhances sensitivity of anterior pituitary gonadotrophins to GnRH
  • Selective inhibition of FSH leads to surge in LH
21
Q

What is the relationship between the surge in LH and the production of progesterone?

A
  • Granulosa cells become responsive to LH
  • Progesterone production begins
22
Q

Identify 3 processes which occur during ovulation

A
  • Mature oocyte extruded through the ovary capsule
  • Meiosis I is completed
  • Meiosis II commences
23
Q

Describe the hormone levels immediately after ovulation

A
  • Follicle is luteinised and secretes oestrogen and progesterone in large quantities
  • Inhibin continues to be produced and LH is suppressed
24
Q

Why is LH production suppressed after ovulation?

A

Negative feedback due to the presence of large quantities of progesterone

25
Q

What characterises the waiting phase?

A

Further gamete development is suspended

26
Q

In the luteal phase, what hormones are produced by the corpus luteum?

A
  • Progesterone
  • Oestrogen
  • Inhibin
27
Q

What causes the corpus luteum to regress?

A

The absence of a surge of LH

28
Q

What are the two stages in the uterine cycle?

A
  • Proliferative phase
  • Secretory phase
29
Q

What is the endometrium and what does it do?

A
  • The endometrium is the lining of the uterus
  • It is a specialised epithelium that responds to ovarian hormones
30
Q

Explain how the uterus responds to the following:

  • Oestrogen
  • Progesterone
A
  • Responds to oestrogen by proliferating
  • Responds to oestrogen and progesterone by secreting
31
Q

Label the following structures on the uterus below:

A
  • M = myometrium
  • E = endometrium
  • F = functional layer
  • B = basal layer
32
Q

What is the myometrium?

A

The myometrium is the muscular wall of the uterus

33
Q

What does the functional layer of the uterus do?

A

The functional layer is hormone responsive and sheds if no pregnancy occurs

34
Q

What does the basal layer of the uterus do?

A

The basal layer provides the source from which a new functional layer is developed

35
Q

Describe the appearance of the uterus during the early proliferative phase

A

Early proliferative: glands sparse, straight

36
Q

Describe the appearance of the uterus during the late proliferative phase

A

Late proliferative: functional layer has doubled, glands now coiled

37
Q

Describe the appearance of the uterus during the early secretory phase

A

Early secretory: endometrium max thickness, very pronounced coiled glands

38
Q

Describe the appearance of the uterus during the late secretory phase

A

Late secretory: glands adopt characteristic “saw-tooth” appearance

39
Q

What effect does the regression of the corpus luteum have?

A
  • Dramatic fall in gonadal hormones relieves negative feedback
  • Menstrual cycle starts again
40
Q

What happens when fertilisation occurs?

A
  • Syncytiotrophoblast produces human chorionic gonadotrophin
  • Corpus luteum is maintained by placental hCG
41
Q

What is the significance of human chorionic gonadotropin?

A

​- Made by the embryo to signal its presence

  • Exerts a luteinising effect
42
Q

What role does the corpus luteum have in pregnancy?

A
  • It produces steroid hormones to support the pregnancy
  • It regresses once the placenta can produce sufficient quantities of steroid hormones to control the HPO axis
43
Q

Illustrate the relationship between the ovarian and menstrual cycles

A
44
Q

Identify the 6 effects of oestrogen in the follicular phase

A
  • Fallopian tube function
  • Thickening of endometrium
  • Growth & motility of myometrium
  • Thin alkaline cervical mucus forms
  • Vaginal changes
  • Changes in skin, hair, metabolism
45
Q

Identify the 6 effects of progesterone in the luteal phase

A
  • Further thickening of endometrium into secretory form
  • Thickening of myometrium & reduction of motility
  • Thick acidic cervical mucus forms
  • Changes in mammary tissue
  • Increased body temperature
  • Metabolic and electrolyte changes
46
Q

What is the normal duration of the menstrual cycle?

A

21 – 35 days

47
Q

What causes variations in the menstrual cycle?

A
  • Variation in the length of the follicular phase
  • Luteal phase strictly controlled to 14 days (± 2)
48
Q

Identify 4 factors which affect the menstrual cycle

A
  • Pregnancy
  • Lactation
  • Emotional stress
  • Low body weight

(LUSUMA) COPY Reproductive System (21 decks)

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