The Menstrual Cycle

What is the first step involving hormonal regulation at the beginning of the menstrual cycle?

1. At the beginning of the menstrual cycle, the plasma concentration of estradiol, progesterone, and inhibin B are low. 2. FSH concentrations are increased causing primary to Graafian follicle development. 3. This in turn resilts in increasing plasma estradiol (+estrone) and inhibin B levels in blood. 4. Rising plasma estrogens stimulate regeneration of endometrium after menses.

What are the changes that occur during the secretory phase of the menstrual cycle and what are they caused by?

1. Changes in the endometrium are caused by increased progesterone and estrogen levels and are aimed at prepping the endometrium for the blastocyst if pregnancy occurs. 2. The endometrial glands become coiled, accumulate glucogoen, and start secreting glycoprotiens and mucopolysaccharides. 3. Endometrial stroma is edematous. 4. Spiral arteries grow at a greater rate than the thickness of endometrium and become even more coiled.

What effects does progesterone have on the uterus/vagina?

1. Conversion of endometrium into a secretary structure capable of maintaining an implanted blastocyst. 2. Decreased uterine motility, decreases excitability of myometrial cells and their sensitivity to oxytocin. 3. Decrease in the quantity of cervical mucus and return of the thick mucus plug.

What causes the switch from positive feedback of estrogens at the end of the follicular phase to the negative feedback in the luteal phase?

1. Due to progesterone which at higher levels is a potent inhibitor of GnRH from the hypothalamus.

What immune response is recruited for the destruction of the superificial layer of endometrium during menses and how?

1. Endometrial stromal and epithelial cells produce IL-8 which attracts neutrophils by chemotaxis. 2. Invading neutrophils release matrix metalloproteinases which degrade the endometrial interstitial matrix. 3. This process is further accelerated by the release of matrix metalloproteinases from endometrial stromal cells. 4. All this results in formation of tissue fragments which are then extruded with blood from ruptured blood vessels.

What is the fourth step in the hormonal regulation of the menstrual cycle that occurs during late Follicular and early Luteal phase?

1. Estradiol levels transiently decreases during late follicular phase but remain elevate, and increases again in luteal phase. 2. Luteal phase is also characterized by high progesterone and increased inhibin A. 3. Simultaneously, LH and FSH levels are low, indication that progesterone, estradiol, (Hypo/Pit) and Inhibin A (Pit) exert negative feedback.

What occurs to cause menstrual bleeding?

1. It is a response to destruction of corpus luteum of the previous menstral cycle and the resulting sharp decrease in progesterone level in blood. 2. Withdrawal of progesterone stimulates prostaglandin synthesis in endometrium. 3. PGF2 causes intense vasoconstrition of spiral arteries resulting in ischemia and destruction of superficial decidua functionalis layer.

What is the third step in the hormonal regulation of the menstrual cycle that occurs near the end of the Follicular phase?

1. Near the end of the follicular phase, high concentrations of estradiol lasting for several days cause a switch from negative to positive feedback, and estradiol stimulates LH and FSH secretion. 2. This leads to a surge in LH, and a smaller increase in FSH secretion. 3. Ovulation occurs 10-12 hours after the spike of LH. 4. Unexplained peak in inhibin B.

What is the starting and ending point of the Secretory phase of the menstrual cycle?

1. Ovulation is the starting point of the secretory phase of endometrium which coincides with the luteal phase in the ovary. 2. The secretory phase of endometrium ends at the onset of menstrual bleeding.

What are the steps involved in the proliferative phase of the menstrual cycle?

1. Regeneration of the thick endometrium is stimulated by rising estrogen levels in blood. 2. By the 5th day of menses, the thin basalis layer is covered by epithelium. 3. This is followed by proliferation of vascular endothelial, stromal, and glandular cells. 4. Towards the end of the proliferative phase, the endometrium becomes edematous.

What is the Second step in the hormonal regulation of the menstrual cycle?

1. Rising levels of Estrogen initialy inhibit LH and FSH secretion by negative feedback at the hypothalamus and pituitary. 2. In addition, rising plasma levels of inhibin B inhibit FSH secretion from the anterior pituitary.

What effects does Estrogen have on the Ovaries and related hormones?

1. Sensitization of ovaries to gonadotropins. 2. Regulation of gonadotropin secretion.

What is the timing for the proliferative phase of endometrium?

1. Starts with the first day of menstrual bleeding, and ends at the time of ovulation.

What effects does Estrogen have on the Uterus/Vagina?

1. Stimulation of growth of the myometrium and endometrium. 2. Increased uterine blood flow. 3. Increased sensitivity of uterine muscle to oxytocin. 4. Production of copius, watery cervical mucus. 5. Maintenance of the thick vaginal mucose and the acidic vaginal pH.

What affects does Estrogen have on the body as a whole normally and in development?

1. Stimulation of mammary gland growth and developement. 2. Female body configuration due in part to estrogen. 3. Estrogen promotes epiphysial closure. 4. Increased libido.

What effects does progesterone have on the body as a whole?

1. Stimulation of mammary gland growth and development. 2. Regulation of gonadotropin secretion.

What is the normal duration for the menstrual cycle and what causes there to be variation?

1. The duration of menstrual cycle in most women is 24-35 days. 2. Variation in cycle length are mainly due to differences in the length of the follicular phase. 3. The luteal phase is consistently 13-15 days long.

What is the fifth and final step in the hormonal regulation of the menstrual cycle that occurs at the end of the luteal phase?

1. The end of the luteal phase is associated with a fall of progesterone, estradiol, and inhibin A. 2. Simultaneously, FSH levels increase setting a stage for the next menstrual cycle.

What are the two phases of endometrial changes during the menstrual cycle, and what phases do they correspond with in the ovaries?

1. The endometrial changes during the menstrual cycle are divided into proliferative phase and secretory phase. 2. These phases correspond to follicular and luteal phase in the ovary, respectively.

What are the official start designations for the menstrual cycle and the proliferative phase?

1. The first day of menstrual bleeding is designated as day 1 of menstrual cycle and day 1 of proliferative phase of endometrium. 2. The proliferative phase ends at the time of ovulation and its duration corresponds to that of the follicular phase in the ovary.

What are the characteristics of the glands and the surrounding tissue found during the proliferative phase of the menstrual cycle?

1. The glands in the proliferative phase are straight and tubular, and the increasing thickness of the endometrium is supplied by straight arteries and spiral arteries.

What are the roles of FSH and LH?

1. FSH alone is responsible for the early maturation of the primary ovarian follicles. 2. FSH and LH together are responsible for final maturation of the ovarian follicles. 3. LH is necessary for the formation and maintenance of corpus luteum of menstrual cycle.

What are the two parts to the Endometrium and what occurs to them during menses?

1. The superficial 2/3 is the decidua functionalis. It proliferates and is shed with each menstrual cycle. 2. The deep portion adjacent to myometrium is the decidua basalis. It does not proliferate, but instead is the source of endometrial regeneration after each menses.