Which gland is primarily responsible for producing testosterone?

The testes are the primary gland responsible for producing testosterone, a crucial hormone for the development of male reproductive tissues, such as the testes and prostate, and for promoting secondary sexual characteristics, including increased muscle and bone mass, and the growth of body hair. Testosterone production in the testes is stimulated by luteinizing hormone, which is produced by the pituitary gland. However, it is the testes that are the main site of testosterone synthesis, specifically by the Leydig cells within the testes.

The adrenal gland does contribute a small amount of testosterone production, but it is not the primary source. The pituitary gland plays a crucial regulatory role by producing hormones that stimulate the testes but does not produce testosterone itself. Similarly, the thyroid gland is involved in regulating metabolism and does not have a direct role in testosterone production. Thus, the correct answer highlights the specific and primary function of the testes in male hormone production.