Gastrointestinal Motility

Q-1. Pacemaker of the GIT is located in
a) Cardiac end of stomach
b) Long muscle of small intestine
c) Pyloric end of stomach
d) Fundus of stomach

Answer: Pyloric end of stomach
Explanation:
Basic electrical rhythm in GI is initiated by interstitial cells of Cajal, stellate mesenchymal pacemaker cells with smooth muscle like features.
Except in the esophagus and proximal portion of the stomach, smooth muscle of the gastro-intestinal tract has basic electrical rhythm.
Important point:
These cells are located in the circular muscle layer.

Q-2. Migratory motor complex reappear after an interval of
a) 30 min
b) 70 min
c) 90 min
d) 120 min

Answer: 90 min
Explanation:
The migrating motor complex is a distinct pattern of electromechanical activity observed in gastrointestinal smooth muscle during the periods between meals.
The migrating motor complex is initiated by motilin, migrates aborally at the rate of about 5 cm/min and occurs at intervals of approximately 90 min.
Important point:
Gastric secretion, bile flow and pancreatic secretion increase during each MMC.

Q-3. Entero-gastric reflex is caused by all, except
a) Duodenum distension
b) Alkaline pH in duodenum and hormones
c) Increased osmolality of Chyme
d) Products of protein digestion and H+ bathing duodenal mucosa

Answer: Alkaline pH in duodenum and hormones
Explanation:
Enterogastric reflex is the reflexive inhibition of gastric secretion; initiated by the arrival of Chyme in the small intestine.
Fats, carbohydrates and acid in duodenum inhibit gastric acid and pepsin secretion and gastric motility via neural and hormonal mechanisms. The hormone involved is probably peptide YY. CCK has also been implicated as an inhibitor of gastric emptying.
Important point:
Hyper-osmolality of duodenal contents initiates decrease in gastric emptying which is probably neural in origin.

Q-4. Factors responsible for causing diarrhoea after vagotomy are A/E
a) Rapid gastric emptying
b) Hypo-acidity in duodenum
c) Irregular peristalsis
d) None

Answer: None
Explanation:
Causes of post vagotomy diarrhoea:
Irregular peristalsis
Rapid gastric emptying
Decreased gastric acid secretion (Lead to hypo-acidity in duodenum)

Q-5. Chyme is propelled forward in small intestine by
a) Segmentation
b) Haustrations
c) Peristalsis
d) Migratory motor complex (MMC)

Answer: Peristalsis
Explanation:
Intestinal motility:
There three types of muscular contraction.
Peristalsis:
It propels the intestinal contents (Chyme) toward the large intestines.
Segmentation contractions:
It moves Chyme to and fro and increases its exposure to mucosal surface.
Tonic contractions are relatively prolonged contractions that in effect isolate one segment of the intestine from another.

Q-6. Small intestinal peristalsis is controlled by
a) Myenteric plexus
b) Meissner’s plexus
c) Vagus nerve
d) Para-sympathetic system

Answer: Myenteric plexus
Explanation:
Myenteric plexus (Auerbach’s plexus) is primarily concerned with motor control. It is situated between and innervates outer longitudinal and middle circular muscular layers.
Important point:
Meissner’s plexus (Sub-mucosal plexus) is situated between middle circular layer and mucosa and concerned with control of intestinal secretion.

Q-7. Maximum postprandial motility is seen in:
a) Ascending colon
b) Transverse colon
c) Descending colon
d) Sigmoid colon

Answer: Sigmoid colon
Explanation:
Frequency of basic electrical rhythm of colon, increases along the colon, from about 2/min at the ileo-cecal valve to 6/min at the sigmoid.
The increased postprandial contractility is greater in the sigmoid than in the transverse colon.
Important points:
Colonic motility and transit are quiescent during fasting and the transverse colon acts as a mixing and storage area.
The fat component of meal is the major stimulus to colonic contractions, whereas protein ingestion inhibits colonic contractions.

Q-8. While doing sigmoidoscopy, if the rectum is inflated with gas increased peristalsis is seen in
a) Whole colon
b) Proximal colon
c) Distal colon
d) Whole intestine

Answer: Distal colon
Explanation:
The least amount of air insufflation required to maintain an open lumen is preferable in performing flexible sigmoidoscopy. Air insufflation activates defecation reflex.
Defecation reflex:
Distension of rectum-> stimulates a reflexive contraction in the sigmoid colon (Distal colon) and rectum, relaxation of the internal anal sphincter and contraction of the external anal sphincter