The Menstrual Cycle Flashcards
A high frequency of GnRH pulses (one every 60-90 mins) is going to selectively promote the secretion of which hormone?
LH
A low frequency of GnRH pulses (one pulse every 120 mins) is going to selectively promote the secretion of which hormone?
FSH
Define Luteolysis.
- When the Corpus Luteum regresses and dies in the the absence of fertilization and implantation
- Leads to a drastic decline in levels of progesterone, estrogen, and inhibin A by day 24 of the menstrual cycle
A rise in FSH is going to cause what to happen in the ovary?
- Recruitment of Large Antral Follicles
- These follicles produce low levels of Estrogen and Inhibin B
Explain why the LH/FSH ratio is going to slowly increase throughout the follicular phase.
- Slow rise in estrogen and inhibin B will decrease FSH secretion
- Loss of High levels of PROGESTERONE will cause an increase in GnRH pulses; thus, secreting more LH
What is the Ovary’s response to a decline in FSH?
Follicular Atresia (except for the dominant follicle)
The dominant follicle is going to survive because it has the highest number of FSH receptors on it. What else happens to the dominant follicle?
- Produce increasing amounts of Estradiol-17B and Inhibin B during the second half of the follicular phase
- FSH will also induce the expression of LH receptors in the mural granulosa cells
Explain the mechanism underlying the midcycle LH surge in the Anterior Pituitary.
- High Levels of Estrogen will exert a POSITIVE Feedback on the gonadotrope, producing the midcycle LH surge
- Occurs largely at the level of the PITUITARY
Describe the three outcomes that are occuring in the ovary in response to the LH surge.
- Primary Oocyte will complete meiosis I and arrests at Metaphase of meiosis II
- Wall of the follicle and of the ovary at the stigma is broken down and the free-floating Cumulus-oocyte complex is kicked out of the ovary. Normally occurs 32-36 hours after the onset of LH surge.
- Mural Granulosa cells and Thecal Cells are reconstructed to form the CORPUS LUTEUM
How does the mature Corpus Luteum exhibit negative feedback on the Pituitary Gonadotrope?
- Rising levels of Progesterone, Estrogen, and inhibin A are going to provide the Negative Feedback to the Pituitary Gonadotrope
- HIGH Progesterone levels will BLOCK any Positive Feedback that Estrogen could provide
What is required for normal Corpus Luteum function? How many days will it take the corpus luteum to regress? Describe the overall changes in hormone levels that will take place if there is no pregnancy.
- Corpus Luteum will become insensitive to LH signaling unless it receives it from another source (hCG from an implanted embryo)
- Corpus Luteum will normally regress in 14 days
- Progesterone and Estrogen levels will start to decline by about 10 days within the Luteal Phase
What happens when you remove the negative feedback at the end of the menstruation cycle?
Increase in FSH and the cycle will start all over again!
Describe the frequency of GnRH pulses over the menstrual cycle.
Second Half of Follicular Phase: Increase Pulses
Luteal Phase: Decrease Pulses
Define: Thelarche, Adrenarche and Menarche.
Thelarche: Breast Development
Adrenarche: Increase in Adneral Androgen Secretion
Menarche: Beginning of Menstrual Cycles
Describe the Pattern of Gonadotropin levels throughout the life of a Female.
Childhood: FSH and LH levels are going to be low
Puberty: FSH and LH are going to increase but ONLY at night
Reproductive Years: FSH and LH are going to be increased both day and night
Menopause: FSH and LH are both HIGH
What are the two cycles that are happening during the menstrual cycle?
- Ovarian Cycle
2. Endometrial Cycle
During which days of the menstrual cycle do the Follicular and Luteal Phases occur?
- Follicular Phase: 0-14 Days
- Luteal Phase: 14-28 Days
Describe the feedback mechanism of Estrogen at LOW and HIGH hormone concentration levels.
List the functions of Estrogen.
- Stimulate Bone and Muscle Growth
- Stimulation of Endometrial Growth
- Maintain Female Secondary Characteristics
- Maintain Glands
Name the three hormones that the Corpus Luteum is going to secrete.
- Estrogen
- Inhibin (Inhibits FSH)
- Progesterone (Inhibits GnRH & stimulates endometrial growth)