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Figure 2. Follicular phase diagram of hormones and their origins. Follicle-stimulating hormone (FSH) is secreted by the anterior pituitary gland (Figure 2). FSH secretion begins to rise in the last few days of the previous menstrual cycle, [3] and is the highest and most important during the first week of the follicular phase [4] (Figure 1).
Follicle-stimulating hormone is typically measured in the early follicular phase of the menstrual cycle, typically day three to five, counted from last menstruation. At this time, the levels of estradiol (E2) and progesterone are at the lowest point of the menstrual cycle .
During the early and mid-follicular phase, FSH is secreted to promote growth and proliferation of the granulosa cells, which increases GnSAF concentrations. [14] Once the dominant ovarian follicle has been selected at mid-follicular phase, the non-dominant follicles undergo atresia. [15]
A rise in pituitary FSH caused by the disintegration of the corpus luteum at the conclusion of a menstrual cycle precipitates the recruitment of five to seven class 5 follicles to participate in the next cycle. These follicles enter the end of the prior menstrual cycle and transition into the follicular phase of the next one. The selected ...
The follicular phase (or proliferative phase) is the phase of the menstrual cycle during which the ovarian follicles mature. The follicular phase lasts from the beginning of menstruation to the start of ovulation. [12] [13] For ovulation to be successful, the ovum must be supported by the corona radiata and cumulus oophorous granulosa cells. [14]
During the follicular phase, inhibin B is the predominant form, with its levels rising in parallel to the growth of the dominant follicle. This increase in inhibin B, along with rising estrogen levels, contributes to the suppression of FSH secretion, which is critical for the selection of a single dominant follicle.
The sex steroid production begins with follicle-stimulating hormone (FSH) from the anterior pituitary, stimulating granulosa cells to convert androgens (coming from the thecal cells) to estradiol by aromatase during the follicular phase of the menstrual cycle. [1]
In the early follicular phase, uterine contractions in the non-pregnant woman occur 1–2 times per minute and last 10–15 seconds with a low intensity of usually 30 mmHg or less. This sub-endometrial layer is rich in estrogen and progesterone receptors. [3] The frequency of contractions increases to 3–4 per minute towards ovulation.