**Question:** Ovulation is due to surge of: September 2006, 2010

**Core Concept:** Ovulation is the process of releasing an egg from the ovary, which occurs during the menstrual cycle and is essential for fertilization to occur in humans.

**Why the Correct Answer is Right:** Ovulation is primarily triggered by the surge in luteinizing hormone (LH) levels. LH is a hormone secreted by the anterior pituitary gland, under the influence of the hypothalamic hormone, gonadotropin-releasing hormone (GnRH). This mechanism ensures that ovulation occurs near the peak of the follicle growth and maturation, increasing the likelihood of successful fertilization.

**Why Each Wrong Option is Incorrect:**

A. Follicle-stimulating hormone (FSH): While FSH is also produced by the anterior pituitary gland and stimulates follicle growth, it is not responsible for triggering ovulation.

B. Oxytocin: This hormone is involved in uterine contractions during childbirth and labor, not ovulation.

C. Thyroid-stimulating hormone (TSH): TSH is produced by the pituitary gland and regulates thyroid hormone production, not ovulation.

D. Testosterone: Testosterone is a sex hormone primarily responsible for male sex characteristics and not directly related to ovulation.

**Clinical Pearl:** Understanding the intricate interplay between GnRH, FSH, LH, and their respective target hormones (FSH, LH, and testosterone) is crucial for understanding menstrual cycles, fertility, and related clinical scenarios like infertility evaluation and treatment planning.

**Correct Answer:** September 2006 (corresponding to the surge of luteinizing hormone - LH).

Ovulation is primarily driven by the surge in luteinizing hormone (LH) levels, which signals the final maturation and release of the dominant follicle containing the mature egg from the ovary. This surge occurs in response to the hypothalamic hormone gonadotropin-releasing hormone (GnRH).