Gastric And Small Intestinal Motility Flashcards
Orad portion of stomach
. Accepts ingested material during swallowing (receptive relaxation of fundus)
. Stores chyme (adaptive relaxation)
Caudad portion of stomach
. Regulates gastric emptying
. Delivering food to the small intestine at a rate appropriate for optimal digestion and absorption of nutrients
When does the orad stomach relax during digestion?
. 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
Gastric emptying involves ____
. 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
Peristaltic contractions of caudad stomach
. 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
Functions of retropulsion
. Mixes gastric contents
. Reduces particle size
. Emulsifiers dietary fat
Rate of gastric emptying is determined by ____
. 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
The rate of gastric emptying is inc. when ___
. 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.
Particles in stomach
. 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
Effect of duodenum particles on rate of gastric emptying
. Dec. rate of gastric emptying
. Acidic chyme, fat digestion, hypertonic chyme, and distension of duodenum slow gastric emptying
Ileal brake
. Nutrients in ileum slow gastric emptying
. Long neural reflexes and GI hormone PYY in charge of this
Secretin
. 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
Gastrin
. Inc strength of antral construction
. Stimulates SI motility
. Inc. frequency of pyloric contractions to ultimately inc. rate of gastric emptying
Gastroparesis
. 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
Purposes of phasic contractions of SI
. 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
Small intestinal phasic contractions before food enters occur as result of ____
. Long neural reflex
As chyme enters the SI, what reflex is activated?
. 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
Segmentation
. 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
Peristalsis in small intestine
. 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
Migrating motility complex (MMC)
. 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
Phases of MMC
. 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
APs produced during phases of MMC
. 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
Concentration of motilin during MMC phases
. 1: low plasma conc. Of motilin
. 2: medium plasma conc. Of motilin
. 3: high plasma conc. Of motilin
Nausea is result of ____
. Subthreshold activation of vomiting pathways
. Nausea and salivation accompany vomiting
