Gastric and Small intestine Motility Flashcards
2 functional areas of the stomach
Orad and Caudad
Orad
fundus and upper portion; receptive relaxation to receive bolus, Adaptive relaxation to store chyme
Caudad
lower portion and antrum; regulates gastric emptying at a rate appropriate for digestion and absorption
Receptive relaxation (long neural reflex)
the orad stomach is highly compliant and can receive large volumes of food without increasing gastric pressure
Adaptive relaxation (short and long neural pathway)
the orad stomach relaxes when the caudad stomach is distended by gastric contents
adaptive relaxation promotes retropulsion by
providing a pressure gradient
Peristaltic contractions of the caudad stomach function to
mix chyme, emulsify fats, reduce food particle size, amd propel contents toward pylorus, delivery to small intestine at appropriate rate
Sieving (emptying the stomach)
pylorus opens and SMALL (<2mm) particles enter duodenum
Retropulsion
trailing contraction forces larger particles near pylorus through a small opening to forcefully break them up
Leading contraction
closes pylorus
trailing contraction
forces contents through small space with great pressure
Retropulsion function
mix gastric contents, reduce particle size, and emulsify fats
Factors that determine gastric emptying
motilities of stomach and duodenum, diameter of pylorus, composition of particles in the lumen of stomach and small intestine
Factors that increase gastric emptying
increased orad distention, increased caudad contractions, large pylorus diameter, increased PNS, decreases SNS
Factors that decrease gastric emptying
increased SNS, decreased PNS, duodenal distention
Particles in stomach - liquids
empty immediately
Particles in stomach - smaller particles <2 mm
empty faster than larger particles
Particles in stomach - peptides
increased gastrin = increased gastric emptying
Particles in duodenum
decrease gastric emptying via feedback inhibition
Particles in duodenum - Acidic chyme
H+ by secretin
Particles in duodenum - Fat
slows for digestion by CCK
Particles in duodenum - hypertonic chyme
long and short reflexes slow for reabsorption
How do particles in the ileum affect gastric emptying?
decreases it via long reflexes and GI hormones
Gastroparesis
impaired or delayed gastric emptying w/o obstruction
Causes of gastroparesis
Autonomic Neuropathy, vagotomy, and medications
Treatments for gastroparesis
small meals, viscous foods, low fat diet, protokinetic meds (erythromycin)
Diabetic with gastroparesis
erythromycin treatment
Type I diabetic eats meal high in fat, his insulin delivery should be
20% at beginning of meal, 80% afterwards
Function of phasic contractions in small intestine
mix chyme, expose chyme to enterocyte brush border for digestion-secretion, move chyme towards colon
2 types of phasic contractions in the small intestine during digestive period
segmentation and peristalsis
Long neural reflexes in small intestine
cause phasic contractions before chyme enters small intestine
Short neural reflexes ins mall intestine
due to chemosensitive and mechanosensitive IPANs that determine the rate of phasic contractions to optimize digestion and absorption
Segmentation phasic contraction functions to
mix contents of small intestine and to expose contents to mucosa for digestion and reabsorption (NON-PROPULSIVE)
Peristalsis phasic contraction functions to
propel chyme through the small intestine; ahead of chyme, longitudinal muscle contracts while circular relaxes, and behind the chyme, longitudinal relaxes and circular contracts (PROPULSIVE)
Phasic contraction frequency is limited by
slow waves
Slow waves control maximal frequency of phasic contractions during
digestive phase and fasting
Location of Migrating Motility Complex
gastric antrum and small intestine (not colon)
Function of Migrating Motility Complex
Sweep undigested and unabsorbed contents into the large intestine
MMC sweeps
undigested particles from stomach to ileum (80-120 min) and recurs every 75-90 min
3 phases on MMC during fasting
- no phasic contractions
- random, irregular phasic contractions
- 3-6 min of intense phasic contractions
Activity front
phase 3 of MMC
Phase 1
no slow waves produce AP, no phasic contractions, low motilin
Phase 2
50% of slow waves are accompanied by AP and phasic contractions, medium motilin
Phase 3
100% of slow waves produce AP with phasic contractions, high motilin
Motilin follows pattern of phases
low concentration during phase 1, medium during phase 2, and high during phase 3
Emesis (vomiting)
reflex controlled by brainstem; accompanied by nausea and salivation, nausea only if sub threshold, to remove noxious substances, can lead to hypokalemia and metabolic alkalosis
Causes of vomiting
overdistention (stomach or duodenum), emetic chemicals, activation of chemoreceptor trigger zone, tactile receptos in pharynx, vestibular system, higher brain centers (trauma, anxiety)
Serotonin
released by endocrine cell of upper small intestine, activates afferent vagal nerves
Emetic chemicals
activate chemoreceptors in stomach and duodenum
Chemoreceptor Trigger zone (area postrema)
stimulated by chemicals triggers vomiting
Vomiting reflex
reverse peristalsis, relaxation of pylorus and contraction of duodenum, contents flow backwards, LES and UES open, increased intra-abdominal pressure and decreased intra-thoracic pressure
What determines the rate of phasic contractions once food enters small intestines?
IPANs and short neural reflexes
Purpose of MMC
during fasting (interdigestive period) sweep unabsorbed contents into colon to prevent bacteria overgrowth
Plasma concentration of motilin is directly related to ___________ during MMC
frequency of phasic contractions, phase of MMC during fasting
During MMC, the slow wave frequency
does NOT change
Erythromycin
motilin agonist, causes gastric emptying, diarrhea