By the end of this lesson
- Describe a peristaltic wave.
- Explain roles of circular and longitudinal muscle.
- Relate peristalsis to mixing and directed movement.
BIG QUESTION
How can food travel through the oesophagus even when a person is upside down?
Peristaltic waves are active muscular movements; gravity may assist but does not drive transport.
A wave moves the bolus
peristalsisWaves of muscle contraction in the wall of the gut (or other tubes) that push food along. is a coordinated wave of contraction and relaxation in the gut wall. Circular muscle contracts behind a bolus, narrowing the lumen and pushing contents forward.
Circular muscle ahead relaxes, while longitudinal contraction can shorten and widen the receiving section.
The movement is active
Gut smooth muscle uses energy and is coordinated by nerves and local signals. Peristalsis can move contents against gravity.
Mucus reduces friction and protects the lining, helping the bolus move without damaging tissue.
Mixing improves digestion
Contractions also mix contents with digestive secretions and bring products into contact with the absorptive epithelium.
Sphincters regulate passage between regions, preventing uncontrolled movement or reflux.
Muscle actions during a wave
Use position relative to the bolus.
| Location/action | Effect on lumen | Consequence |
|---|---|---|
| Circular muscle behind contracts | Lumen narrows. | Pushes bolus forward. |
| Circular muscle ahead relaxes | Lumen remains open. | Allows bolus to enter. |
| Longitudinal muscle ahead contracts | Section shortens/widens. | Helps receive and advance bolus. |
| Sphincter contracts | Passage closes. | Controls regional flow. |
Language that earns precision
- peristalsis
- Coordinated muscular waves moving contents along the alimentary canal.
- circular muscle
- Muscle arranged around the gut that narrows the lumen when contracted.
- longitudinal muscle
- Muscle arranged along the gut that shortens a section when contracted.
- bolus
- A lubricated mass of chewed food that has been swallowed.
- sphincter
- A ring of muscle controlling passage between regions.
Common misconceptions
Claim: Gravity moves food down the oesophagus.
Correction: Peristalsis actively propels it and can work against gravity.
Claim: Muscles in front of the bolus contract shut.
Correction: The region ahead relaxes or widens to receive it.
Claim: Peristalsis occurs only in the oesophagus.
Correction: Coordinated movements occur throughout much of the alimentary canal.
Match the answer to the command word
Use “behind” and “ahead” of the bolus to make direction unambiguous.
Link muscle contraction to lumen diameter and pressure.
Use peristalsis—not gravity—to explain movement in any body position.
Recall, apply, then justify
Explain how peristalsis moves a bolus through the oesophagus.
Hint
Contrast the gut wall behind and ahead.
Suggested marking points
- Circular muscle contracts behind the bolus.
- This narrows the lumen and raises pressure behind it.
- Muscle ahead relaxes/longitudinal muscle shortens the section.
- A coordinated wave propels the bolus forward.
Explain one way gut contractions improve digestion besides transport.
Hint
Think contact.
Suggested marking points
- Contractions mix food with digestive secretions.
- This increases contact between enzymes and substrates or products and the absorptive surface.
Why can swallowing still move food when a person is inverted?
Hint
Active muscular wave.
Suggested marking points
- Peristalsis is generated by coordinated muscle contraction.
- It can create pressure and movement independently of gravity.
Explain why uncoordinated muscle contraction could impede rather than accelerate gut transport.
Planning hint
A wave needs spatial order.
What a strong design includes
- Contraction on both sides could trap the bolus.
- Contraction ahead could close the lumen.
- Loss of sequential timing removes the pressure gradient.
- Poor mixing can reduce enzyme–substrate contact.
- Coordination, not simply force, determines effective movement.