Autonomic nervous system

The autonomic nervous system (ANS) regulates involuntary bodily functions including heart rate, blood pressure, digestion, and respiration. It is traditionally divided into sympathetic (fight-or-flight) and parasympathetic (rest-and-digest) divisions, with the enteric nervous system commonly recognized as a semi-autonomous third division regulating the gastrointestinal tract. In longevity science, ANS function is assessed via HRV, baroreflex sensitivity, and heart rate recovery, since dysautonomia and chronic sympathetic dominance are implicated in cardiovascular disease and accelerated biological aging.