Question

When does peristalsis start?

- at the voluntary phase of the swallowing reflex

- At the involuntary phase of the swallowing reflex

- In the middle of esophagus

- As soon as ingestion starts

Answer 1

Peristalsis is the contractions and relaxation of the food resulting in wave like movement. Contraction is due to contraction of circular muscles and relaxation of longitudinal muscles. Relaxation is caused by simultaneous contraction of longitudinal muscles and relaxation of circular muscles. Peristalsis starts from esophagus and proceed down to stomach and then to intestine. The mechanism of initiation of peristalsis in esophagus can be summarized as below:

After the food is chewed into bolus via mastication, it gets swallowed and enters esophagus. Waves of contraction or peristaltic waves started to act upon the food. Two types of peristalsis occurs in esophagus namely primary and secondary peristalsis. Primary peristalsis starts in the upper portion of esophagus which is under the voluntary control and is devoid of both Auerbach and Meissner's plexus, so it belongs to the voluntary phase of the swallowing reflex. It starts when the bolus enters the esophagus during swallowing and forces it downward to enter into the stomach. The process of food movement downwards often may stuck due to slow peristaltic wave of contraction, hence it induces the strectch receptors in the esophagus to stimulate a response in the form of secondary peristalsis where the left over food particles start to move downward in this process. Thus the secondary peristalsis is under the involuntary phase of the swallowing reflex. Hence, peristalsis starts from the upper portion of esophagus at the voluntary phase of the swallowing reflex.