Which of the following glands is primarily responsible for hair growth?

The gonads are primarily responsible for hair growth due to their production of sex hormones, such as testosterone and estrogen. These hormones play a crucial role in the development and maintenance of secondary sexual characteristics, including body hair. In males, increased levels of testosterone can lead to more prominent hair growth, particularly on the face and body, while in females, estrogen influences hair distribution and density.

The other glands mentioned have different functions. The thyroid gland is primarily responsible for regulating metabolism and does not directly influence hair growth. The pituitary gland, while it produces hormones that can affect other glands, is more of a regulatory center rather than a direct influencer of hair growth. Lastly, the hypothalamus plays a pivotal role in maintaining homeostasis and regulating various bodily functions but does not directly control hair growth. Hence, the gonads are key players in the hormonal control of hair growth.