Describe the physiology of gastric emptying (80% of marks). Outline the gastrointestinal effects of erythromycin (20% of marks).

[Click here to toggle visibility of the answers]

College Answer

This question was best answered by using a classification system, or systematic approach to 
gastric emptying. Receptive relaxation (triggered by movement of food through the pharynx 
and oesophagus), vagally mediated relaxation of fundus and upper body of stomach, the 
pyloric pump (being intense peristalsis in lower body of the stomach that results in stomach 
emptying) and the pyloric sphincter(a circular muscle that allows water and fluids to easily 
pass through but restricts solids until it is mixed in chime to almost fluid consistency).
Candidates were also expected to mention regulatory factors e.g. food volume through 
myenteric reflexes / gastrin stimulatory motor effects and enhanced pyloric pump, acidity 
and osmolality of chyme in duodenum, presence of breakdown products of protein and fat 
through enteric nervous system, sympathetic and parasympathetic nervous systems and 
hormones such as cholecystokinin, secretin and gastric inhibitory peptide. Erythromycin is a 
commonly used prokinetic and some knowledge of effects was expected (e.g. the fact that it 
stimulates motilin receptors on GI smooth muscle and promote onset, frequency and 
duration of migrating motor complex, from stomach and spreading caudally thus increasing 
gastric emptying).