Flashcards in Exam #4: Female Reproductive Physiology II Deck (33):
Outline steroidal production during the follicular phase. What regulates the production of steroidal hormones during this phase?
- Theca (that surround the follicle with granulosa cells) cells synthesize androstenedione in response to LH
- Androstenedione is converted to estradiol in granulosa cells (enzymes), which is controlled by FSH
*****IT takes BOTH cells, theca & granulosa to make estradiol & BOTH FSH & LH
What is the effect of estrogen production during the follicular phase?
- Negative feedback on the hypothalamus & anterior pituitary (primarily) to keep the levels of LH & FSH relatively low
- Estrogen also causes proliferation of the endometrium
What is the effect of the rise in FSH in mid-follicular phase?
1) Development of the granulosa and theca cells
2) Increase in steroid production
3) Extremely rapid follicle growth
What is the difference between the theca externa and theca interna cells?
Theca externa= capsule of the follicle
Theca interna= hormone producing
In the follicular phase, how many mature follicles actually become ready for ovulation?
Only one dominant or mature follicle actually becomes ready for ovulation, the rest undergo atresia
What causes the atresia of the non-dominant follicles?
Decline in FSH that may be induced by Inhibin B
*****This is how we get just one follicle for ovulation
What happens during the follicular phase in regards to the endometrium?
Prolifeation of the uterine endometrium
- stromal cells
- growth of endometrial glands
- blood vessel development
- mucus secretion
*Note that this is regulated by estrogen
When does estrogen peak?
Just before day 14 i.e. just before ovulation
What is the effect of the estrogen peak?
Positive feedback on HPG axis, which results in a surge of gonadotropin or LH/ FSH
When is there a peak of LH & FSH? What happens?
- Day 14
- Ovulation i.e. rupture of the follicle & release of the oocyte
What is absolutely required for ovulation?
LH surge at Day 14
NO LH = NO ovulation
What happens to progesterone levels after ovulation?
Rise i.e. progesterone levels rise in the Luteal Phase
What effect does progesterone have on basal body temperature?
Increase in basal body temp
****Thus, basal body temperature can be a marker ovulation
What are basal body temperature measurements used for?
Determining if ovulation has occurred i.e. increased basal body temperature is indicative that ovulation has occurred
What is the corpus luteum?
A temporary endocrine gland that secretes estradiol and progesterone; this the remnant of the rupture follicle
- Luteum= lipid i.e. cholesterol for steroid production
When does the CL reach a mature state?
7-8 days following ovulation
What happens to steroidal production during the luteal phase?
Production of BOTH estradiol and progesterone
- LH binds theca-lutein cells & stimulates andostenedione formation
- Androstenedione is again converted to estradiol in the lutenized granulosa cells
- Additionally, there is an upregulation of the genes necessary to make progesterone in the lutenized-granulosa cells
Thus, BOTH the theca & granulosa cells respond to LH
What changes are seen in granulosa cells that helps them form progesterone?
- Upregulation of LDL receptors for cholesterol
- Enzymes necessary to form progesterone from cholesterol
- LH receptors on granulosa cells
What happens to the endometrial lining during the Luteal Phase?
Differentiation and secretory development that is regulated by PROGESTERONE
*This is the SECRETORY phase that gets ready for implantation
What are the key endometrial changes that occur during the luteal phase?
- Increased complexity of vascular and glandular structures
- Accumulation of substances in glands
- Deposition of lipids and glycogen in stromal cells
- Increased blood supply
Describe the feedback mechanisms of the Luteal Phase.
- Progesterone & inhibin A exert a negative feedback at the level of the ANTERIOR PITUITARY
*****Gonadotropin production declines & results in a decline in steroid production
When does the CL begin to regress? What does it become?
- 26th day
- Corpus albicans
What does the decline in estrogen & progesterone production of the Luteal Phase result in?
- Release of proteolytic enzymes that cause tissue lysis
- Increase in prostaglandin production that increases myometrial contraction
Note that progesterone normally INHIBITS these actions i.e. prostaglandins
What causes the menstrual cycle to restart again?
Low steroid levels relieve the negative inhibition on the HPG axis & gonadotropin production begins to rise again
If fertilization occurs, what allows invasion into the endometrium?
The blastocyst expresses multiple enzymes that allow invasion
How is steroid production maintained if there is fertilization?
If IMPLANTATION occurs, CL does NOT regress
- hCG stimulates ovarian steroidogenesis
What receptors does hCG bind to?
LH receptors; thus, hCG mimincs LH to maintain steroidogenesis & CL is maintained
When is there a transition in the dependence of the CL for steroids and the placenta?
Draw the relative concentrations of the gonadotropins during the menstrual cycle.
Draw the relative concentrations of the steroid hormones during the menstrual cycle.
What are the age related changes in hormone release that occur in puberty?
1) Low amplitude nocturnal pulses of gonadotropin release
2) Increased steroid production in response, which causes a number of physiological changes
What is menarche indicative of hormonally?
Estrogen-mediated endometrial growth