What is the primary hormone secreted by the zona fasciculata of the adrenal cortex?

The primary hormone secreted by the zona fasciculata of the adrenal cortex is cortisol. This layer of the adrenal cortex is responsible for producing glucocorticoids, which play critical roles in metabolism, immune response regulation, and stress response.

Cortisol acts to increase glucose availability in the bloodstream by promoting gluconeogenesis in the liver and influencing the metabolism of carbohydrates, proteins, and fats. It helps the body respond to stress and maintain homeostasis. This hormone also has anti-inflammatory properties, making it essential in regulating the immune system.

In contrast, the zona glomerulosa, which lies above the zona fasciculata, primarily secretes aldosterone, a mineralocorticoid involved in sodium and water retention. The zona reticularis, located beneath the zona fasciculata, is where androgens and small amounts of estrogens are produced, but these hormones are not the primary products of the zona fasciculata itself. Thus, the function and secretions of these other zones are distinct from the cortisol produced in the zona fasciculata.