What is the primary function of the adrenal glands?

The primary function of the adrenal glands is to produce hormones that play essential roles in regulating various bodily functions, including metabolism, immune response, and the body's response to stress. The adrenal glands consist of two main parts: the adrenal cortex and the adrenal medulla. The adrenal cortex produces steroid hormones such as cortisol, which helps manage stress and influences metabolism and immune response, as well as aldosterone, which is crucial for regulating blood pressure and fluid balance. The adrenal medulla produces catecholamines like adrenaline, which are involved in the body's fight or flight response.

In contrast to the primary function of the adrenal glands, other options refer to processes regulated by different systems or organs. For example, while blood pressure regulation is influenced by hormones released by the adrenal glands, it is not their sole or primary function. Additionally, neurotransmitter production is primarily the responsibility of the nervous system and specific glands such as the pineal gland and pituitary gland. Heart rate is primarily controlled by the autonomic nervous system, specifically through the actions of the heart and associated nervous pathways rather than directly attributed to the adrenal glands. Thus, the comprehensive role of the adrenal glands in hormone production for metabolism, immune response, and stress response underscores why option C is the correct answer.