Which hormone directly stimulates the adrenal gland's cortex?

The hormone that directly stimulates the adrenal cortex is adrenocorticotropic hormone (ACTH). ACTH is produced by the pituitary gland and its primary role is to regulate the production of cortisol by the adrenal cortex. Cortisol is essential for various bodily functions, including the stress response, metabolism, and immune response. ACTH acts on specific receptors in the adrenal cortex, triggering the release of cortisol and other glucocorticoids, thereby playing a critical role in maintaining homeostasis during times of stress.

In contrast, growth hormone primarily affects growth and metabolism but does not have a direct effect on the adrenal cortex. Thyrotropin, also known as thyroid-stimulating hormone (TSH), is responsible for stimulating the thyroid gland to produce thyroid hormones and does not influence the adrenal glands. Luteinizing hormone plays a key role in reproductive function, particularly in regulating the menstrual cycle and ovulation in females, and it does not have a direct relationship with the adrenal cortex. This context helps to clarify why ACTH is the correct choice among the options provided.