The ovarian cycle is initiated by :
The ovarian cycle has two phases: the follicular phase and the luteal phase. The follicular phase starts with the development of ovarian follicles, which is driven by follicle-stimulating hormone (FSH). FSH stimulates the growth of the follicles in the ovary. Then, as the follicles mature, they produce estrogen. Once estrogen levels are high enough, this triggers a surge in luteinizing hormone (LH), which leads to ovulation. After ovulation, the ruptured follicle becomes the corpus luteum, which is maintained by LH during the luteal phase.
So the initiation of the ovarian cycle would be the start of the follicular phase, which is driven by FSH. The options might include FSH, LH, estrogen, progesterone, or maybe another hormone. Since the correct answer is FSH, I need to explain why that's the case.
Common wrong options might be LH, because it's involved in ovulation, but the cycle starts with FSH. Estrogen and progesterone are produced by the follicles and corpus luteum, not initiating the cycle. Maybe another option is hCG, but that's related to pregnancy, not the normal cycle.
The core concept here is the role of FSH in initiating follicular development. The clinical pearl is to remember that FSH starts the follicular phase, leading to estrogen production and the LH surge. High-yield fact: FSH is the key hormone for starting the cycle each month.
**Core Concept**
The ovarian cycle begins with the follicular phase, which is initiated by follicle-stimulating hormone (FSH). FSH stimulates the growth and maturation of ovarian follicles, leading to estrogen production and eventual ovulation. This process is part of the hypothalamic-pituitary-ovarian axis.
**Why the Correct Answer is Right**
FSH is secreted by the anterior pituitary gland and acts on granulosa cells of the ovarian follicles. It promotes follicular development, increases estrogen synthesis via aromatase enzyme activity, and supports theca cell recruitment. This follicular growth culminates in a midcycle LH surge, triggering ovulation. FSH is the primary driver of the follicular phase, making it the correct initiation signal.
**Why Each Wrong Option is Incorrect**
**Option A:** *Luteinizing hormone (LH)* is incorrect because it primarily triggers ovulation and corpus luteum formation, not the initial follicular phase.
**Option B:** *Estrogen* is incorrect as it is a product of follicular development, not the initiating hormone.
**Option C:** *Progesterone* is incorrect because it dominates the luteal phase post-ovulation, not the follicular phase.
**Clinical Pearl / High-Yield Fact**
Remember the sequence: **FSH starts follicles → estrogen rises → LH surge triggers ovulation**. Confusing FSH with LH is a common exam trap—FSH initiates the cycle, while LH completes it. Use the mnemonic **"