Which sequence correctly lists the parts of the HPG axis?

Which sequence correctly lists the parts of the HPG axis?

• A. Hypothalamus, pituitary gland, and gonads (testes and ovaries).
• B. Gonads, hypothalamus, pituitary.
• C. Pituitary, hypothalamus, gonads.
• D. Gonads, pituitary, hypothalamus.

Answer: (A)

The main concept here is how the HPG axis is organized in a directional signaling cascade: hypothalamus → pituitary gland → gonads. The hypothalamus releases GnRH, which prompts the pituitary to secrete gonadotropins (LH and FSH). Those hormones then act on the gonads (testes or ovaries) to stimulate the production of sex hormones and gametes. This order—brain initiating the signal, pituitary relaying it, gonads executing the response—is the reasoning behind the correct sequence: hypothalamus first, then the pituitary, then the gonads. In puberty, this cascade ramps up, leading to increased sex hormone production and maturation. Sequences that start with the gonads or place the hypothalamus after the pituitary don’t reflect how the axis is regulated, since the hypothalamus is the starting point that controls the rest of the pathway.

The main concept here is how the HPG axis is organized in a directional signaling cascade: hypothalamus → pituitary gland → gonads. The hypothalamus releases GnRH, which prompts the pituitary to secrete gonadotropins (LH and FSH). Those hormones then act on the gonads (testes or ovaries) to stimulate the production of sex hormones and gametes. This order—brain initiating the signal, pituitary relaying it, gonads executing the response—is the reasoning behind the correct sequence: hypothalamus first, then the pituitary, then the gonads. In puberty, this cascade ramps up, leading to increased sex hormone production and maturation.

Sequences that start with the gonads or place the hypothalamus after the pituitary don’t reflect how the axis is regulated, since the hypothalamus is the starting point that controls the rest of the pathway.