Final answer:
External control of GI tract motility and secretion is regulated by the autonomic nervous system, with sympathetic activation reducing and parasympathetic activation increasing these activities.
Step-by-step explanation:
The external control of motility and secretion in the gastrointestinal (GI) tract is primarily managed by the autonomic nervous system, which includes the sympathetic and parasympathetic nervous systems. Sympathetic activation, often associated with the fight-or-flight response, tends to decrease GI secretion and motility, conserving energy for immediate physical demands. Conversely, parasympathetic activation, related to the rest-and-digest state, leads to an increase in GI secretion and motility, enhancing the digestion and absorption process. Neural controls within the alimentary canal include various sensors like mechanoreceptors, chemoreceptors, and osmoreceptors that help regulate digestive functions by sensing changes and stimulating appropriate reflexes. Intrinsic control involves the enteric nervous system, with its myenteric and submucosal plexuses, which governs the GI tract's local reflexes and plays a role in the gut's peristaltic movements and secretion regulation.