Motility of GI Tract Flashcards
Where is the submucosal plexus located?
Between the circular muscle and the submucosa
What is the function of the circular and longitudinal muscles?
- Circular muscle contraction decreases the diameter of the tube
- Longitudinal muslce contraction decreases the length of the tube
What do slow waves do within GI tract?
- Slow waves are depolarization and repolarization of the membrane and it doesn’t always end up in an AP
- They set the frequency of depolarization
- Appearance of an AP determines if there will be a contraction
- Slow waves aren’t APs!
- Neural activity and hormonal activity modulate APs and strength of contraction
What are phasic contractions?
- Periodic contractions followed by relaxation for the mixing and propulsion of food through the GI tract
What are tonic contractions?
- Sustained contractions without regular periods of relaxation, seen in sphincters
- These only need to be opened at certain times, so there is constant contraction closing the valve until something needs to pass
How do slow waves AP and contractions relate in the smooth muscle?
- The greater number of AP’s on top of slow waves results in a larger contraction
How does Ach affect slow waves?
It increasese the amplitude of slow waves and the number of AP’s
How does NE affect slow waves?
Decreases amplitude of slwo waves
What three things cause increase in amplitude of slow waves?
- Stretch
- Ach
- Parasympathetics
What two things cause hyperpolarization decreasing amplitude of slow waves?
- Sympathetics
- NE
What does the submucosal (Meissner’s) plexus control?
GI secretions and local blood flow
What does the myenteric (Auerbach’s) plexus control?
GI movements
What are Interstitial cells of Cajal?
- Pacemaker for GI smooth muscle
- They generate and propagate slow waves, and these occur spontaneously and spread via gap jxn
Describe how swallowing works.
- Oral phase is voluntary and initates the swallowing process
- Pharyngeal phase is involuntary. The soft palate is pulled up moving the epiglottis relaxing the upper esophageal sphincter, peristaltic waves are initiated in the pharynx and food is propelled through the sphincter
- Esophageal phase is involuntary and is controlled by swallowing reflex and ENS
What controls the involuntary swallowing reflex?
Medulla:
- the food moves in the pharynx and afferent sensory input occurs via CN9 and 10 to the swallowing center in the medulla, which sends info to the brainstem nuclei giving efferent input to the pharynx
What are the two types of peristaltic waves? (describe them)
- Primary: continuation of pharyngeal peristalsis controlled by the medulla.
- cant occur with a vagotomy
- Seconday: only occcurs if primary wave fails to empty the esophagus or if gastric contents reflux into esophagus. The medulla and ENS help. This can occur in absence of oral and pharyngeal phases and can occur after a vagotomy
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What are two challenges of the intrathoracic esophagus and how are they solved?
- Keeping air out of the esophagus at the upper end and keeping acidic gastric contents out of lower end
- UES and LES are closed except when food is passing
How does achalasia affect the esophagus, what causes it, what can it result in clinically?
- It impairs peristalsis, the LES relaxation during swallowing is incomplete resulting in a backup of food and increase in LES resting pressure
- Decreased numbers of ganglion cells in myenteric plexus and degeneration involves neurons producing NO/VIP. This results in damage to nerves in esophagus preventing it from passing food into stomach
- Results in regurgitation dysphagia, heart burn and chest pain
What is GERD, what causes it, what happens in GERD, what are the complications?
- Changes the barrier btw the esophagus and stomach because the LES relaxes abnormally or is weak.
- Occurs due to motor abnormalities that result in low pressures in the LES seen if the intragastric pressure increases
- Constant reflux and inflammation leads to GERD resulting in:
- acid, pepsin and bile flowing back up esophagus
- heartburn and acid regurgitation
- Complications:
- GI bleeding, Irritation of esophagus lining, scar tissue, Barrett’s esophagus
43 yr old male with htn and 5 yr history of dyshpagia. Food and occasionally liquids get stuck at upper sternum with every meal. He can get food down with repeated swallowss or drinking water. He has spontaneous regurgitation of clear foamy liquid and undigested food in his mouth especially when bending over. He has lost 8 lbs. He denies heartburn or odynophagia and admits he can’t belch. PMH is unremarkable other than 20 PPY. What is going on? What test would be helpful?
- Achalasia, the lower esophageal sphincter is not opening properly. The food never reaches the stomach which is why he has undigested food regurgitation. There is nerve damage to fibers that produce VIP and NO which cause vasodilation and the nerurons that release Ach are spared.
- Barium swalllow and esophgeal motility study would be helpful
Describe receptive relaxation in the orad region of stomach.
- Decrease in pressure of the stomach and increase in volume of the orad region mediated vagovagal reflex
