170. What is true regarding menstrual cycle?
(1) Follicular phase is followed by menstrual phase.
(2) Lack of menstruation may be an indicative of
Segnancy
(3) Menstrual cycle is absent in monkeys.
(2) Lagk
(4) Progesterone surge induces ovulation
Answers
Explanation:
Definition/Introduction
The follicular phase of the female menstrual cycle includes the maturation of ovarian follicles to prepare one of them for release during ovulation. During the same period, there are concurrent changes in the endometrium, which is why the follicular phase is also known as the proliferative phase.
Issues of Concern
Follicular Phase
The duration of the menstrual cycle varies and occurs every 21 to 35 days, with an average span of 28 days. Oligomenorrhea describes infrequent menstrual periods and cycles lasting more than 35 days. Polymenorrhea refers to frequent menstrual periods and cycles lasting less than 21 days. It is important to note that the duration of the follicular phase can differ depending on the length of the cycle, while the luteal phase is usually stable and lasts 14 days. Based on a 28-day cycle, the follicular phase measures from the first day of menstruation (day 0) until the beginning of ovulation (day 14). When the previous menstrual cycle completes, and the corpus luteum breaks down, the levels of estrogen, progesterone, and inhibin A will decrease. This chain of events will cause positive feedback to the hypothalamus and anterior pituitary, and a subsequent pulsatile release of GnRH and FSH into circulation. This increase in FSH will stimulate the granulosa cells of the ovaries to recruit several follicles from each ovary. These follicles will complete maturation, and only one Graafian follicle will go through ovulation during that cycle. The increase in FSH also stimulates the secretion of Inhibin B by the granulosa cells. Inhibin B will eventually blunt the secretion of FSH toward the end of the follicular phase. Inhibin B levels will be highest during the LH surge before ovulation, and will quickly taper off after.
The level of FSH available can vary based on the age of the female. The functioning of the ovaries weakens with increasing age, which causes less inhibin production in the previous luteal phase. The decreased inhibin levels stimulate a larger release of FSH compared to that of a younger female. These increasing levels of FSH cause more active recruitment of ovarian follicles, which can increase the occurrence of more than one ovulation per cycle. Since the follicles get recruited at an increased rate, the overall duration of the follicular phase will decrease, and the follicle released for ovulation will be immature. Due to these age-related changes in the early follicular phase, physicians can assess suspected infertility by checking serum FSH and estradiol levels around day 3 of the cycle. Also, the ovarian reserve can be predicted by monitoring serum levels of anti-Mullerian hormone (AMH) made by the granulosa cells, as this hormone plays an important role in folliculogenesis. AMH levels can be monitored at any point during the menstrual cycle.
The mid-follicular phase will begin with a rise in levels of estradiol and inhibin B produced by the ovarian follicles in response to an increase in FSH; this will result in negative feedback that will decrease the levels of FSH. It is during this time that the selection of the follicle intended for ovulation takes place. This follicle is called the dominant follicle. Different theories suggest how the dominant follicle is determined. One idea is that the follicle expressing the highest amount of FSH receptors will be the one to promote its growth and ovulate, while the other follicles are suppressed and undergo atresia. Another theory states that the anti-Mullerian hormone (AMH) plays a role in the selection of the dominant follicle.
As a response to the rise in FSH levels during the early follicular phase, there will be a proliferation of granulosa cells. This rise in the number of granulosa cells will cause a concurrent rise in FSH receptors on the cells. The increased FSH levels allow the granulosa cells to produce estradiol, which recruits LH receptors on granulosa cells as well. With LH receptors now present, the granulosa cells will produce small amounts of progesterone and 17-hydroxyprogesterone. The progesterone released by the granulosa cells regulates granulosa cell proliferation and ultimately slows follicular growth.
As the follicular phase comes to an end, estradiol levels will rapidly increase. With this increase in estradiol, the negative feedback loop will switch to positive feedback. There is no definitive answer as to why this switch in feedback happens, but suggestions are that kisspeptin neurons play a role. The positive feedback from the estradiol will stimulate the hypothalamus and the anterior pituitary, and there will be a surge in LH, signaling the end of the follicular phase and the beginning of ovulation. I HOPE YOU BETTER UNDERSTAND KEEP LEARNING STAY HEALTHY AND PLEASE MARK ME BRAINLIST