The parasympathetic nervous system's purpose is often referred to as "rest and digest." As part of this purpose, parasympathetic innervation increases motility in the digestive tract to move food through. However at the same time, slowing gastric motility and peristalsis is important for absorbing nutrients, which is accomplished by enterogastrones like secretin.
So on one hand, the PSNS promotes more motility to move things through the digestive tract. On the other, certain hormones are released in response to the presence of food that slow down motility for better absorption.
- If one of the main purposes of the PSNS is to promote digestion (and thus I would subsequently think absorption), why does it cause increased motility, which gives less time for digestion and absorption?
- Is it important during digestion to sometimes increase or decrease motility? If so, how does it related to the PSNS and SNS in terms of when either happens?