Final answer:
The sympathetic branch of the autonomic nervous system decreases enzyme secretion by the pancreas as part of the fight-or-flight response.
Step-by-step explanation:
The branch of the autonomic nervous system that acts to decrease enzyme secretion by the pancreas is the sympathetic branch.
The sympathetic nervous system is responsible for the fight-or-flight response and generally restricts the activity of enteric neurons, leading to a decrease in pancreatic enzyme secretion. On the other hand, the parasympathetic nervous system, which promotes the rest-and-digest response, increases GI secretion and motility.
Sympathetic activation is part of the fight-or-flight response and it restricts the activity of enteric neurons, which in turn decreases gastrointestinal (GI) secretion and motility. Therefore, during sympathetic activation, there is a reduction in the secretion of digestive enzymes from the pancreas. In contrast, the parasympathetic nervous system enhances enzyme secretion and GI motility as part of the rest-and-digest response, especially during the cephalic and gastric phases of gastric secretion.