Peristalsis

In the syllabus and the exam

Peristalsis is used to explain how food moves through the alimentary canal independently of gravity, driven by alternating contraction and relaxation of circular and longitudinal muscle layers in the gut wall. Exam questions typically ask candidates to describe how a bolus of food is squeezed forward, with circular muscle contracting behind the food while longitudinal muscle contracts ahead of it, creating a wave that travels along the oesophagus, stomach and intestines. Candidates are also expected to connect peristalsis to the general theme of adaptation for function, since the layered muscular wall of the gut is one of a small set of digestive-system adaptations tested alongside villi and enzyme secretion. A common mistake is describing peristalsis only as the gut squeezing food forward, without mentioning the two muscle layers or the coordinated wave-like pattern, which SPM mark schemes specifically reward.

Example

Peristalsis continues to push a swallowed mouthful of food down the oesophagus even if a person is lying upside down.

Related terms

DigestionVillusAssimilation

Source:SRC-DSKP-EN