University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

145

Pages:

2
Author:

Mariam A. A.

• • • Stomach Emptying Most of the stomach contractions mix the food with gastric juices Pylorus is tonically contracted to a point where fluid easily passes, but unprocessed food does not Small volumes of food lead to weaker contractions, large volumes trigger stronger contractions Regulation of stomach emptying by the duodenum • Control by duodenum prevents the movement of excess food into intestine (too much food limits absorptive capacity) • Inhibition of stomach emptying by duodenum is mediated by nervous reflexes and hormones o Nerve reflexes that inhibit stomach emptying are triggered by: ▪ Distention of duodenum ▪ High acidity of the chyme ▪ Hypertonic and hypotonic chyme (particularly hypertonic) ▪ Breakdown products of proteins and to a lesser extent, fat ▪ Irritation of the duodenum • Clinician’s corner: Gastroparesis is where there is paralysis of the stomach or delayed gastric emptying → most commonly women, caused by diabetes, post-surgery, idiopathic Movement in small intestine • Stretching of the intestine causes peristaltic contractions that cause forward movement and mixing • Movement is slow to allow greater absorption of nutrients (1cm/min) → takes 3-5 hours for food to pass through small intestine • Hormones that increase peristaltic activity: gastrin, CCK, insulin, motilin, serotonin • Hormones that inhibit intestinal motility are secretin and glucagon • Peristaltic rush o Normally peristalsis in small intestine is weak (slow movement of food) o Irritation (e.g. during infectious diarrhoea) causes rapid and powerful peristalsis o Involves ANS and intrinsic control of myenteric plexus Defaecation • Faeces entering the rectum stretches the walls and stimulates the myenteric plexus to initiate peristaltic contractions in the descending colon downward • Myenteric plexus relaxes the internal sphincter + external sphincter is voluntary relaxed → defaecation • This is augmented by parasympathetic activity • There is relaxation of the puborectalis muscle → anal-rectal angle straightens