**Question:** FSH acts on which of the following:

A. Ovarian follicles
B. Testicular germ cells
C. Sertoli cells
D. Leydig cells

**Correct Answer:** A. Ovarian follicles

**Core Concept:** Follicle-Stimulating Hormone (FSH) is a glycoprotein hormone secreted by the anterior pituitary gland, specifically the anterior pituitary gland's follicle-stimulating hormone-releasing hormone (FSHR) receptor. FSH plays a crucial role in regulating the development and function of ovarian and testicular cells.

**Why the Correct Answer is Right:** FSH primarily acts on ovarian follicles, which are small cavities in the ovaries that contain oocytes (egg cells). In females, FSH helps stimulate the growth and maturation of ovarian follicles, leading to the release of an egg during ovulation. In males, FSH plays a role in the development and function of Sertoli cells, which support the growth of germ cells (spermatogenesis), but this is not the primary action of FSH.

**Why Each Wrong Option is Incorrect:**

A. Ovarian follicles: As mentioned above, FSH does stimulate ovarian follicles, but the correct answer is A, not D.
B. Testicular germ cells: FSH does play a role in testicular germ cell development, but the primary action is on ovarian follicles.
C. Sertoli cells: While FSH does affect Sertoli cells, the primary action is on ovarian follicles, making D the correct answer.
D. Leydig cells: FSH does stimulate Leydig cells in males, but the primary action is on ovarian and Sertoli cells, not Leydig cells.

**Clinical Pearl:** Understanding the specific actions of hormones like FSH helps in diagnosing and treating endocrine disorders, such as oligospermia (low sperm count in men) and polycystic ovary syndrome (PCOS) in women. In PCOS, elevated FSH levels indicate impaired ovarian responsiveness to FSH, which may lead to the development of multiple small follicles instead of a single large one.