GI Peristalsis and Motility MCQs

During swallowing when the peristaltic wave sweep down the esophagus the gastroesophageal sphincter relaxes so that the bolus of food can pass into the stomach. Distance of the Lower Esophageal Sphincter from the upper incisors is 37.5cm the lower esophageal sphincter is tonically active but relaxes on swallowing. This tonic activity of the LES between meals prevents reflux of gastric contents into the esophagus. its tone is under neural control by the parasympathetic nervous system. Contraction of LES is caused by the release of acetylcholine from the vagus and release of NO and VIP from interneurons innervated by other vagal fibers causes it to relax. Ref: Fundamentals of Human Physiology By Lauralee Sherwood page 447. Ganong's Review of Medical Physiology, 24e CHAPTER

Ans. D: Medulla Vomiting is believed to be controlled by two distinct brain centres— the vomiting centre and the chemoreceptor trigger zone—both located in the medulla oblongata. The vomiting centre initiates and controls the act of emesis, which involves a series of contractions of the smooth muscles lining the digestive tract

MMC aids in clearing the stomach and small intestine of luminal contents in preparation for the next meal Reference: Ganong, 25th edition page no.497

MMC is initiated by motilin. Circulating level of motilin increases at intervals of approximately 90-100 min in the interdigestive state Reference: Ganong, 25th edition page no.497

Functions of nitric oxide Vasodilation Inhibition of platelet aggregation vascular remodeling Penile erection Glutamate release in hippocampus - Has got a role in synaptic plasticity (learning and memory) Relaxation of lower esophageal sphincter (LES) - defective release of nitric oxide in lower end of esophagus leads to Achalasia cardia GI smooth muscle relaxation Reference: Ganong, 25th edition page. 593

Contracting segment behind the bolus - neurotransmitters responsible are substance P and acetylcholine Relaxing segment in front of the bolus neurotransmitters responsible are nitric oxide and vasoactive intestinal peptide Reference: Ganong, 25th edition page no.501

Most important stimulus for peristalsis is the stretch of the gut wall Reference: Ganong, 25th edition page no.501

The movements of the colon are coordinated by the BER of the colon. The frequency of this wave, unlike the wave in the small intestine, increases along the colon, from about 2/min at the ileocecal valve to 6/min at the sigmoid. Reference: Ganong, 25th edition page no.503