Gastric And Small Intestinal Motility

Question 1

Orad portion of stomach

Answer 1

. Accepts ingested material during swallowing (receptive relaxation of fundus)
. Stores chyme (adaptive relaxation)

Question 2

Caudad portion of stomach

Answer 2

. Regulates gastric emptying

. Delivering food to the small intestine at a rate appropriate for optimal digestion and absorption of nutrients

Question 3

When does the orad stomach relax during digestion?

Answer 3

. When caudad stomach is distended by gastric contents
. Called adaptive relaxation: short and long neural reflexes
. Provides pressure gradient to promote retropulsion of gastric contents

Question 4

Gastric emptying involves ____

Answer 4

. Peristaltic contractions (sieving and retropulsion) to mix chyme, reduce food size, emulsify fat, and propel contents towards pylorus
. Delivering chyme to SI at the appropriate rate for optimal digestion and absorption of nutrients

Question 5

Peristaltic contractions of caudad stomach

Answer 5

. Begin in body of stomach and move to pylorus
. Inc. in strength and velocity as they approach pylorus
. Leading and trailing peristaltic contractions
. Before leading contraction arrives at pylorus, the pylorus opens (via VIP/NO) and small diameter particles (under 2 mm) and liquids enter duodenum
. Particles sieved according to size
. Leading contraction closes pylorus
. Trailing contraction then forces the retained gastric contents into a small space using great pressure
. Gastric contents forcefully propelled back through small opening

Question 6

Functions of retropulsion

Answer 6

. Mixes gastric contents
. Reduces particle size
. Emulsifiers dietary fat

Question 7

Rate of gastric emptying is determined by ____

Answer 7

. Motility of stomach and duodenum
. Diameter of pylorus
. Composition of particles in lumens of stomach and SI
. All these factors work together to determine overall gastric emptying rate

Question 8

The rate of gastric emptying is inc. when ___

Answer 8

. Distension of orad stomach is inc.
. Force of contractions of caudad stomach is inc.
. Diameter of pylorus is larger
. Segmenting contractions of prox. Duodenum are inhibited
. Activity of PNS n. Is inc.
. Activity of SNS n. Is dec.

Question 9

Particles in stomach

Answer 9

. Liquids begin to empty almost immediately
. Smaller diameter (under 2 mm) solid particles empty faster than larger diameter (over 2mm) solid particles (sieving)
. Peptides inc. the rate of gastric emptying by inc. gastrin secretion
. Distension of orad stomach inc. rate of gastric emptying

Question 10

Effect of duodenum particles on rate of gastric emptying

Answer 10

. Dec. rate of gastric emptying

. Acidic chyme, fat digestion, hypertonic chyme, and distension of duodenum slow gastric emptying

Question 11

Ileal brake

Answer 11

. Nutrients in ileum slow gastric emptying

. Long neural reflexes and GI hormone PYY in charge of this

Question 12

Secretin

Answer 12

. Inhibits peristaltic contractions of caudad stomach
. Further contracts pylorus to ultimately dec. rate of gastric emptying
. Low pH in small intestinal lumen can damage enterocytes
. Emptying is slowed to allow time for neutralization of H ion

Question 13

Gastrin

Answer 13

. Inc strength of antral construction
. Stimulates SI motility
. Inc. frequency of pyloric contractions to ultimately inc. rate of gastric emptying

Question 14

Gastroparesis

Answer 14

. Gastric emptying is impaired or delayed but there is no evidence of obstruction
. Symptoms: include early satiety, bloating, nausea, and vomiting
. Solid emptying is usually affected more than liquid emptying
. Causes: autonomic neuropathy, vagotomy, ICC dysfunction, and med side effects
. Treatment: eating meals that are small in size, more viscous than solid, low in fat
. Prokinetic meds accelerate emptying rate

Question 15

Purposes of phasic contractions of SI

Answer 15

. Thoroughly mix chyme w/ digestive secretions and enzymes
. Expose luminal contents to digestive-absorptive surface of mucosa, the enterocyte brush border
. Net movement: chyme towards colon

Question 16

Small intestinal phasic contractions before food enters occur as result of ____

Answer 16

. Long neural reflex

Question 17

As chyme enters the SI, what reflex is activated?

Answer 17

. Short neural reflex
. Chemosensitive and mechanosensitive IPANS respond to nutrients in lumen and smooth m. Tension to determine rate of phasic contractions required to optimize digestion and absorption

Question 18

Segmentation

Answer 18

. Mixing motility in SI
. Non-propulsive, but redistributes SI contents through mixing and churning and exposes the nutrients to digestive/absorptive surface of the mucosa

Question 19

Peristalsis in small intestine

Answer 19

. Basic propulsive movement
. Involves relaxation of circular m. And contraction of longitudinal m. Ahead of the chyme w/ contraction of circular m. And relaxation of longitudinal m. Behind the chyme
. Spreads out chyme after it first enters the duodenum
. Peristalsis proceeds in aboral direction

Question 20

Migrating motility complex (MMC)

Answer 20

. During fasting
. Sweeps undigested and unabsorbed luminal contents in gastric antrum and small intestine into the large intestine to prevent bacterial overgrowth in SI
. DOES NOT OCCUR IN COLON
. Recurs every 75-90 min
. Replaced by segmentation and peristalsis when person begins to eat

Question 21

Phases of MMC

Answer 21

. 1: no phasic contractions
. 2: random irregular phasic contractions for short time
. 3: 3-6 min of intense phasic contractions w/ propulsion of luminal contends towards the large intestine
. Any undigested particles retain in stomach are emptied into duodenum by phase 3 of MMA
. During each phase, the percent of slow waves assoc. w/ smooth m. Phasic contractions is different but freq. of slow waves doesn’t change

Question 22

APs produced during phases of MMC

Answer 22

. 1: no slow waves produce APs, no smooth m. Phasic contractions
. 2: 50% slow waves produce AP bursts w/ accompanying smooth m. Phasic contractions
. 3: all slow waves produce AP bursts w/ accompanying smooth m. Phasic contractions

Question 23

Concentration of motilin during MMC phases

Answer 23

. 1: low plasma conc. Of motilin
. 2: medium plasma conc. Of motilin
. 3: high plasma conc. Of motilin

Question 24

Nausea is result of ____

Answer 24

. Subthreshold activation of vomiting pathways

. Nausea and salivation accompany vomiting

Question 25

Prolonged vomiting can result in ___

Answer 25

. Fluid and electrolyte imbalances
. Metabolic alkalosis
. Hypokalemia

Question 26

Ways vomiting can be initiated

Answer 26

. Overdistension of stomach and/or duodenum (serotonin released activating afferent vagal nn.)
. Emetic chemical that activate chemoreceptors in stomach duodenum (serotonin released from endocrine cells of upper SI activating afferent vagal nn.)
. Some systemic chemicals may stimulate chemoreceptor trigger zone and initiate vomiting
. Activation of tactile receptors in pharynx
. Vestibular system
. Higher brain center: anticipation, trauma

Question 27

Sequence of events in vomiting reflex

Answer 27

. Reverse peristalsis pushes SI contents from middle of SI towards duodenum
. Orad stomach relaxes and intestinal contents enter stomach due to contraction of duodenum and relaxation of pylorus
. LES and UES relax
. Forces inspiration against closed glottis reduces intra-thoracic pressure
. Diaphragm is lowered, inc. intra-abdominal pressure
. Abdominal mm. Contract ejecting gastric contents into esophagus and out the mouth

Question 28

Etiology of coarsely chewed, undigested food

Answer 28

. Gastric retention: outlet obstruction, gastroparesis

. Esophageal disorder: achalasia, diverticulum

Question 29

Etiology of blood in vomit

Answer 29

. Bleeding from esophagus, stomach, or duodenum