What does the autonomic nervous system control?

The autonomic nervous system (ANS) plays a crucial role in regulating involuntary physiological functions that maintain homeostasis within the body. It primarily controls activities that are not consciously directed, such as heartbeat and contractions of the heart muscle, which are essential for circulating blood. Additionally, the ANS influences bronchial diameter, facilitating proper airflow and gas exchange during respiration.

The correct answer emphasizes these specific functions, highlighting the heart's rhythm and the respiratory system's mechanics, both of which are critical in emergency medical situations. The other options address functions that are indeed important but fall under different body systems or are encompassed by other regulatory mechanisms. For example, blood calcium levels and reflex actions (mentioned in another option) are primarily regulated by the endocrine and reflex pathways, while pupil dilation and body temperature regulation involve additional systems and processes outside the main scope of the ANS's primary responsibilities.