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Flashcards in Menstrual Cycle Deck (42)
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How long is the menstrual cycle?

24-35 days


What is the duration of bleeding?

<8 days


List the HPG Axis

Hypothalamus-->GnRH-->anterior pituitary gonadotrope cells-->FSH and LH-->ovary-->Estrogen and progesterone


What determines what phase the cycle is in with regards to GnRH?

GnRH neuron secretions are pulsatile and vary in amplitude

1. Follicular phase: 60-90min, low amp
2. Luteal phase: 3-5hr, high amplitude


Is the half life of GnRH short or long and how do we control for this in the HPG axis?

Short, GnRH travels through the hypothyseal artery directly to the anterior pituitary or it would degrade in the blood system before it could do its job


Describe the route of the hormones secreted by the hypothalamus to the anterior pituitary

1. Hormones are secreted into primary capillary plexus
2. Hormones go through the portal vein to the anterior pituitary
3. Anterior pituitary hormones are secreted into the secondary capillary plexus


What do FSH, LH, hCG, TSH have in common?

They are glycosylated polypeptides made of up an identical alpha and slightly different beta chain. For this reason, they have cross reactivity with various receptors


What are the two functions of the ovary?

1. To produce estradiol and progesterone
2. To make a competent egg (ie able to be fertilized)


When does oogenesis begin during gestation?



When are there 6 million oocytes?

16-18 wks gestation


How many oocytes do you have at birth?

2 million


How many oocytes do you have at puberty?

300,000 (due to atresia)


How many oocytes do you have after menopause?



What are the two stages of follicle maturation? Describe them

1. Gonadotropin independent stage
-Follicles are constantly being recruited from primordial stage to primary stage

2. Gonadotropin dependent stage
-By the secondary follicle stage, follicles require FSH to grow


What happens to a group of follicles each month?

Each month, a group of follicles respond to rising FSH levels from the pituitary (at the end of the menstrual cycle and beginning of the next cycle) and continue to develop. Eventually, one follicle is selected as the dominant follicle and it will be released with ovulation. The rest undergo atresia.


Name the 7 stages of follicle development

1. Primordial
2. Primary
3. Secondary
4. Preantral (gonadotropin dependent stage begins)
5. Antral
6. Selected
7. Preovulatory


List and describe the 3 functions of FSH

1. Simulates granulosa cell proliferation
-Preantral-->preovulatory stages

2. Stimulates aromatase activity in granulosa cells
-Causing conversion of androgens to estrogens
-So with a rise in FSH levels, get a rise in estrodiol levels

3. Up regulates LH and FSH receptors
-Maybe causing production of more estrodiol?


What is the two cell theory?

Theca cells make androgens that are then transferred to granulosa cells to be aromatized (by aromatase) to estrogen


When are serum estrodiol concentrations largest?

1 day before ovulation


Why do FSH levels decrease?

Before threshold, estrogen results in negative feedback on pituitary and hypothalamus


What happens once estradiol reaches a threshold?

Estrogen feedback becomes stimulatory and results in increase in GnRH pulse frequency causing LH surge leading to the luteal phase


List and describe the 3 functions of LH

1. Causes the release of oocyte from the follicle after 36 hrs

2. Leads to luteinization of granulosa cells with increased production of testosterone
-The luteal phase needs progesterone AND estrogen, alter expression of enzymes and produce both now

3. Causes resumption of meiosis of the oocyte and release of the 1st polar body


What two features signify a mature oocyte?

1. See polar body
2. Arrested in metaphase 2


What do estrogen and progesterone do in the luteal phase?

Suppress gonadotropin release


Where are estrogen and progesterone produced in the luteal phase?

Corpus luteum


What does estrogen do to the uterus?

1. Promotes reconstruction and growth of the endometrium
2. Mitoses become prominent

Glands are lined by low columnar epithelium cells


What does progesterone do to the uterus?

1. Limits growth, mitosis, and DNA synthesis

2. Increases tortuosity of glands, intensified coiling of spiral vessels
-need more blood to uterus for baby

3. Secretion of glycoproteins and peptides into cavity


Around what day after conception does the egg get implanted?

Day 5


What happens during the luteal phase if fertilization does not occur?

1. Corpus luteum degenerates (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

Get menstruation


What happens if fertilization occurs?

1. The embryo makes hCG which maintains the corpus luteum via LH receptors
2. Progesterone and estrogen secretion thus continues and you don't get menstruation
3. The corpus luteum stays for 8-10 weeks, then the placenta takes over making hormones


What happens hormone-wise in the early follicular phase?

There is less E and P so there is a release from negative feedback causing an increase in GnRH pulse frequency and therefore an increase in FSH levels (leading to maturation of follicles)


What happens hormone-wise in the mid follicular phase?

Rising estrogen from the follicle suppresses GnRH secretion and FSH levels decrease


What happens hormone-wise in the Pre-ovulation phase?

E levels reach threshold and there is a shift to positive feedback causing an LH surge


What happens hormone-wise in the post ovulation phase?

Increase in P and E from the corpus luteum leading to a decrease in FSH and LH via negative feedback


What happens hormone-wise in the end luteal phase

Loss of corpus luteum leads to a decrease in P and E, a loss of negative feedback, and therefore an increase in FSH


What produces inhibin?

Inhibin is produced by granulosa cells


What does inhibin do?

1. Decreases pituitary GnRH receptors, blocking FSH synth and secretion
2. Increases LH receptors on theca cells
3. Competes for activin receptor and inactivates activin


Where is activin produced?

Produced in gonads and pituitary


What does activin do?

Augments FSH actions by enhancing GnRH activity in pituitary via inc GnRH receptor production


What superfamily do activin and inhibin belong to?

TGF-B superfamily


What is inhibin comprised of?

One alpha and one beta subunit


What is activin comprised of?

Two beta subunits