Question

The function of pyloric sphincter is to prevent the backflow of food to foodpipe. Then how does vomiting happen?

Answer 1

Vomiting happens due to retroperistalsis which is a reverse peristalsis of the stomach. So cardiac sphincter between stomach and oesophagus relaxes to allow emesis, not the pyloric sphincter between stomach and small intestine.

Explanation:

Vomiting is an involuntary act of forcefully throwing up the contents of stomach through mouth. It occurs due to contraction of smooth muscles present in stomach wall; the contraction may actually originate in wall of duodenum.

There is a vomiting centre in hind brain's medulla oblongata. Irritation of stomach sends afferent impulses to the vomiting centre and the centre in turn sends autonomic (motor) impulse to gastrointestinal wall to initiate retroperistalsis, the reverse of peristalsis and the smooth muscles contract.

Contraction of abdominal wall and diaphragm also take place during vomiting. The cardiac sphincter relaxes, allowing food to move up.