The autonomic nervous system.
D000368:Aged; D001341:Autonomic Nervous System / Q000502:physiology*; D002940:Circadian Rhythm; D005221:Fatigue / Q000150:complications; D006801:Humans; D007022:Hypotension / Q000150:complications; D013564:Sympathetic Nervous System / Q000502:physiology; D014630:Vagus Nerve / Q000502:physiology