Which of the following is NOT a function of the testicles?

The choice regarding the production of estrogen as a function of the testicles is indeed correct because the primary roles of the testicles predominantly revolve around male reproductive functions.

The testicles are responsible for spermatogenesis, which is the process of producing sperm cells. This is a critical function in male fertility. They also secrete testosterone, the main male sex hormone, which plays a vital role in the development of male secondary sexual characteristics, libido, and overall reproductive health. Additionally, the testicles contain structures known as the epididymis, which are responsible for the storage and maturation of sperm.

While the testicles can produce small amounts of estrogen, particularly from the conversion of testosterone, they are not primarily recognized for this function as it is more significant in females. Estrogen production occurs mainly in the ovaries in females, and in males, it is generally produced in peripheral tissues from androgens. Thus, the production of estrogen is not a primary function of the testicles, making this the correct choice for the question.