Lecture 6: The Menstrual Cycle Flashcards Preview

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Flashcards in Lecture 6: The Menstrual Cycle Deck (46)
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1

What is the length of the menstrual cycle?

24-35 days

2

What is the duration of bleeding?

Less than 8 days

3

What is the HPO axis?

Hypothalamic-pituitary-ovarian axis

4

What is the proliferative phase of the menstrual cycle?

The follicular phase
From day 1 – ovulation
Signficance: this is the VARIABLE region where the length of the time can change

5

Which phase of the menstrual cycle is variable?

The Follicular/Proliferative phase

6

What are the hormones that are salient in the HPO (HPG axis)?

1. GnRH (hypothalamus)
2. FSH
3. LH
4. Estradiol (ovary)
5. Progesterone (ovary)

7

What is the significance of the increase in frequency/amplitude of mid-cycle GnRH pulsatile secretion?

Favors the LH surge necessary for ovulation

8

How does the pulsatile secretion of follicular phase compare with luteal phase?

Higher frequency and lower amplitude characterizes follicular phase over luteal phase
Luteal phase is less frequent and high amplitude

9

What secretes GnRH?

GnRH neurons in the hypothalamus

10

What are the 3 key points of hypophyseal-anterior pituitary relationship in HPO axis?

Point 1: When appropriately stimulated, hypothalamic neurons secrete either releasing or inhibiting hormones to the capillary plexus
Point 2: GnRH travels through the portal veins to the anterior pituitary where they stimulate or inhibit release of hormones from ant. Pituitary
Point 3: Anterior pituitary hormones are secreted in the SECONDARY capillary plexus

11

What is the acronym for shit released by anterior pituitary?

FLAT PEG
FSH
LH
ACTH
TSH
Prolactin
Endorphins
Growth hormone

12

What is released by posterior pituitary?

ADH
Oxytocin

13

What cells secrete FSH and LH in pituitary?

The Gonadotrope cells

14

What is the significance of the glycosylated polypeptides?

Alpha and Beta chain are located on the following hormones:
1. FSH
2. LH
3. hCG
4. TSH

15

What is the significance of LH and hCG?

Very similar….
Same alpha chain, different beta chain
Consequence: LH and hCG can act on same receptor
Help to regulate/mess up menstrual cycle

16

What is an oocyte?

Germ cells in the ovary

17

When do women have all their oocytes?

At birth
Has supporting cells (granulosa and theca cells) surrounding them

18

When do follicles begin to be recruited?

20 weeks in utero

19

What is are the key checkpoints in a woman’s reproductive life?

6-8 weeks: oogenesis begins
16-18 weeks: 6 million oocytes
Birth = 2 million oocytes
Puberty = 300,000 oocytes
Menopause = 0 oocyte

20

How are follicles recruited?

They are recruited from the primordial stage to the primary stage
Little is known about the initiation

21

When are follicles gonadotropin dependent?

At the secondary follicle stage

22

What is the significance of FSH?

1. Stimulates granulosa cell proliferation
2. Stimulates aromatase activity in granulosa cells
-stimulates conversion of androgens to estrogens
3. Upregulates FSH and LH receptors

23

How is the follicular phase regulated?

Serum estradiol concentrations peaks 1 day before ovulation
Estrogen results in NEGATIVE feedback on pituitary and hypothalamus
-decreases FSH
Once estradiol reaches a threshold, estrogen feeback becomes STIMULATORY and results in increase in GnRH pulse frequency
-this leads to LH surge
So estrogen can be both inhibitory and stimulatory

24

What is the LH surge?

Cause release of oocyte from follicle 36 hours after beginning of LH surge
-leads to luteinization of the granulosa cells with increased production of progesterone
-causes resumption of meiosis of the oocyte and release of 1st polar body

25

How long does it take for egg to pass from fallopian tube to uterus?

3-4 days

26

When must fertilization occur?

Within 24 hours of ovulation or ovum degenerates

27

How are the gonadotropins inhibited during luteal phase?

Progesterone and estrogen inhibits their release

28

What is the function of estrogen?

1. In the luteal phase, inhibits release of gonadotropins initially, then stimulates LH release for ovulation
2. Promotes reconstruction and growth of the endometrium
3. Glands lined by low columnar epithelium cells
4. MITOSES become PROMINENT

29

What is the function of progesterone?

1. LIMITS growth, mitosis and DNA synthesis
2. Increased tortuosity of glands
-intensified coiling of spiral vessels
3. Secretion of glycoproteins and peptides into cavity

30

What happens in the luteal phase if fertilization does NOT occur?

1. corpus luteum degenerates after 14 days
2. estrogen and progesterone levels fall
3. withdrawal of progesterone causes secretory endometrium to slough
4. As estradiol falls, FSH levels slowly rise again in ABSENCE of negative feedback