Which hormone is primarily produced by the ovaries?

The hormone primarily produced by the ovaries is estrogen. In females, estrogen plays a crucial role in the development and regulation of the reproductive system and secondary sexual characteristics. It is responsible for the menstrual cycle, influencing the growth of the uterine lining during the menstrual cycle, and is also involved in various other functions such as bone health and cardiovascular health.

In contrast, testosterone is predominantly produced by the testes in males but is also present in smaller amounts in females, primarily for functions related to muscle strength and libido. Cortisol is produced by the adrenal glands and is involved in the stress response and metabolism regulation. Insulin is produced by the pancreas and is critical for regulating blood glucose levels.

The prominence of estrogen in ovarian function highlights its essential role in female reproductive health and development, making it the correct answer.