**Question:** Serum inhibin B is secreted by ovarian granulosa cells staying at:

**Core Concept:** Inhibin B is a glycoprotein hormone produced by granulosa cells in the ovaries, primarily in response to follicle-stimulating hormone (FSH) inhibition. It plays a role in regulating follicle development and ovulation.

**Why the Correct Answer is Right:** Inhibin B is produced primarily by granulosa cells in the antral follicles, which are the growing follicles within the ovaries. These follicles are under the influence of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Inhibin B secretion decreases as FSH levels increase, and vice versa.

**Why Each Wrong Option is Incorrect:**

A. Inhibin B is not secreted by ovarian theca cells; this option is incorrect because inhibin B is produced by granulosa cells, not theca cells.
B. This option is incorrect because inhibin B is not secreted by luteinizing hormone-releasing hormone (LHRH) neurons; inhibin B is produced by granulosa cells in response to FSH and LH secretion.
C. This option is incorrect because inhibin B is not secreted by luteinizing hormone (LH); inhibin B is produced in response to LH inhibition, not directly by LH.
D. This option is incorrect because inhibin B is not secreted by the corpus luteum, but rather is produced by granulosa cells in response to FSH and LH inhibition.

**Clinical Pearl:** Monitoring serum inhibin B levels can be useful in assessing ovarian reserve and predicting fertility outcomes. In general, a decrease in inhibin B levels indicates reduced ovarian function, which is associated with decreased fertility potential. This test is often used in fertility clinics as a complementary tool alongside other tests like antral follicle count and anti-Müllerian hormone (AMH) to evaluate ovarian reserve and guide fertility treatment decisions.

**Correct Answer:** D. Inhibin B is secreted by the corpus luteum.

**Explanation:** Inhibin B is a protein hormone produced primarily by granulosa cells in the antral follicles and in response to FSH and LH inhibition. The corpus luteum is a secondary response to the luteinizing hormone (LH) surge during the follicle maturation process. Inhibin B levels decline as the corpus luteum begins to degenerate after ovulation, indicating decreased ovarian function and reduced fertility potential.