Question

The hormone that is primarily responsible for the onset of ovarian activity and puberty, in animals is

• A. LH
• B. FSH
• C. GnRH
• D. Estradiol

Hint:

The onset of puberty is determined by the maturation of the hypothalamus, specifically its ability to produce high-frequency, high-amplitude pulses of GnRH, which then drive the release of LH and FSH.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Puberty in animals is defined as the transition stage when reproductive organs become functional, accompanied by the onset of regular estrous cycles and gametogenesis.
This process is regulated by the hypothalamic-pituitary-gonadal (HPG) axis.

Step 2: Detailed Explanation:
Let us analyze the hierarchy of endocrine triggers in the onset of puberty and ovarian activity:
- During prepubertal development, the hypothalamus is highly sensitive to negative feedback from low levels of estradiol, which keeps the system suppressed.
- The critical step triggering puberty is a decrease in this hypothalamic sensitivity, leading to an increase in the pulsatile secretion of Gonadotropin-Releasing Hormone (GnRH) from the surge and tonic centers of the hypothalamus.
- GnRH is the master regulatory hormone.
- Its increased pulsatile release stimulates the anterior pituitary gland to synthesize and secrete Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH) in a pulsatile manner.
- FSH and LH then act on the ovaries to initiate follicular development (FSH) and stimulate ovulation and corpus luteum formation (LH), resulting in estradiol secretion and the first behavioral estrus.
- Therefore, the primary hormone responsible for initiating the entire cascade of ovarian activity and puberty is GnRH.

Step 3: Final Answer:
The hormone primarily responsible for the onset of ovarian activity and puberty is GnRH.