Physiological Changes in Pregnancy
The following correlate with menstrual changes except? (AIPG 2011)
|B||Vaginal cytology changes|
The ESTROUS CYCLE (also oestrous cycle; derived from Latin oestrus) comprises the recurring physiologicchanges that are induced by reproductive hormonesin most mammalian placental females. Humans undergo a menstrual cycleinsteaD. Estrous cycles start after pubertyin sexually mature females and are interrupted by anestrous phases or pregnancies. Typically estrous cycles continue until death.
The relative pattern of ovarian, uterine, and hormonal variation along the normal menstrual cycle is typical:
a. At the beginning of each monthly menstrual cycle, levels of gonadal steroids are low and have been decreasing since the end of the luteal phase of the previous cycle.
b. With the demise of the corpus luteum, FSH levels begin to rise and a cohort of growing follicles is recruited. These follicles each secrete increasing levels of estrogen as they grow in the follicular phase. This, in turn, is the stimulus for uterine endometrial proliferation.
c. Rising estrogen levels provide negative feedback on pituitary FSH secretion, which begins to wane by the midpoint of the follicular phase. Conversely, LH initally decreases in response to rising estradiol levels, but late in the follicular phase the LH level is increased dramatically (biphasic response).
d. At the end of the follicular phase (just prior to ovulation), FSH-induced LH receptors are present on granulosa cells and, with LH stimulation, modulate the secretion of progesterone.
e. After a sufficient degree of estrogenic stimulation, the pituitary LH surge is triggered, which is the proximate cause of ovulation that occurs 24 to 36 hours later.
f. Ovulation heralds the transition to the luteal-secretory phase.
g. The estrogen level decreases through the early luteal phase from just before ovulation until the midluteal phase, when it begins to rise again as a result of corpus luteum secretion.
h. Progesterone levels rise precipitously after ovulation and can be used as a presumptive sign that ovulation has occurred.
i. Both estrogen and progesterone levels remain elevated through the lifespan of the corpus luteum and then wane with its demise, thereby setting the stage for the next cycle.