What is the role of ACTH (adrenocorticotropic hormone)?

The role of ACTH, or adrenocorticotropic hormone, primarily involves stimulating the adrenal cortex, which is crucial for the synthesis and release of corticosteroids, particularly cortisol. This hormone is secreted by the anterior pituitary gland in response to corticotropin-releasing hormone (CRH) from the hypothalamus and plays a vital part in the body's response to stress.

When ACTH is released, it acts on the outer layer of the adrenal glands, leading to increased production of cortisol and other hormones involved in metabolism, immune response regulation, and blood pressure maintenance. This stimulating effect on the adrenal cortex is essential for the body's ability to respond to stress, making it a central component of the hypothalamic-pituitary-adrenal (HPA) axis.

The other options, while they relate to various hormones and functions in the body, do not pertain to the specific role of ACTH. For instance, ACTH does not directly impact skin pigmentation, growth, or breast development. Instead, those functions are mediated by other hormones, such as melanocyte-stimulating hormone for pigmentation, growth hormone for growth, and estrogen for breast development.