GI Motility Flashcards
What is motility?
Motility is the movement of food down our GI track. The walls and sphincters of the GI tract will contract and relax.
Contraction of the ___________ mix and circulate the food inside the lumen and propels them through the GI tract.
Muscularis propria (inner circular muscle and outer longitudinal muscles, with the myenteric plexus in between)
What is the purpose of the muscularis mucosae?
Has SM. When it contracts, it changes the shape and SA of the epithelium.
The inner circular muscles and the outer longitudinal muscles have DIFFERENT functions.
What are they?
During contraction:
- Inner circular muscles: decrease the diameter of the tract
- Outer longitudinal muscles: decrease the length of the tract
What is a unique feature of GI smooth muscle?
Slow waves: depolarizations and repolarization of the membrane potential, but they are NOT an AP.
When do action potentials occur in the GI smooth muscle?
when the depolarization caused by slow waves moves the membrane potential above the threshold.
In GI smooth muscle, do mechanical responses (tension) and electrical responses occur at the same time?
No. Mechanical responses (tension) occur AFTER the electrical response.
What type of contractions of smooth muscle are KEY for motility in the GI tract?
- Phasic contractions- periods of contraction, followed by relaxation. Thus, they are resp for mixing and propelling food.
- Tonic contractions- constant levels of contraction, without regular times of relaxation.
Mechanical responses (contraction) follows the electrical response. What is in charge of the frequency of contraction and what is in charge of the strength of the contraction?
Frequency is controlled by slow waves,
while the strength of contraction is controlled by how many action potentials/spike potentials are on each wave.
Phasic and tonic are contraction of smooth muscle that are key for motility along the GI tract. What are phasic contractions and where do they occur? (4)
phasic is periodic contractions WITH relaxation
occurs in
- esophagus,
- stomach (antrum),
- SI and ALL tissues involved in mixing
What are tonic contractions and where do they occur? (4)
Tonic maintain a constant level of contraction without relaxation
Eg:
- Stomach (orad),
- LES,
- ileocecal valve,
- internal anal sphincter
How do stretch, ACh, and parasympathetics affect slow waves?
- Increase the amplitude of the slow wave
- Increase the number of AP on the slow wave, creating a larger contraction.
- RESULT: increase motility.
How does NE ( sympathetics) affect slow waves?
- Decrease the amplitude of the slow wave, causing HYPERPOLARIZATION.
–> decrease AP–> decrease motility and digestion
While the frequency of the slow waves is usually set, we can change the magnitude of the __________ in order to change the significance of the action potentials.
slow waves
G.I. movement is primarily controlled by the ____________
myenteric plexus (Auerbach).
bc it has ICC cells
G.I. movement is primarily controlled by the myenteric plexus (Auerbach). What does the submucosal plexus mainly do?
controls GI gland secretions and blood flow
Generally speaking, in the enteric nervous system, sensory information from the ______________ starts a signal, which passes to a _______ neuron, then an __________, then a ________ neuron, creating the output.
Generally speaking, in the enteric nervous system, sensory information from the wall of the gut starts a signal, which passes to a sensory neuron, then an interneuron, then a motor neuron.
Pacemaker cells in the ________ plexus create the spontaneous slow wave activity. What are these cells and what plexus are they located in?
Insterstitial cells of cajal (ICC), located in the myenteric plexus are the pacemaker cells for the GI smooth muscle.
Electrical activity in the ICC drives the frequency of slow waves–> frequency of contractions.
How do the slow waves of the ICC spread rabidly to smooth muscle?
Gap junctions
Mastication, or chewing, is controlled by muscles that are innervated by the?
5th CN (trigeminal)
Mastication is caused by a chewing reflex which is controlled by?
Nuclei in the brain stem. Thus, we mastication is BOTH voluntary and involuntary.
Is swallowing voluntary or involuntary?
Swallowing is a process with both voluntary and involuntary components. It begins voluntary in the mouth at the end of chewing and after that, is involuntary.
What are the 3 phases of the swallowing process and list if they are voluntary or involtary.
1. Oral phase (voluntary)
2. Pharyngeal phase (involuntary)
3. Esophageal phase (involuntary)
Describe the swallowing process.
- Oral phase (voluntary) occurs after we finish chewing.
2 Pharyngeal phase (involuntary): the soft pallate moves upward, moving the epiglottis. This allows the UES to relax. The pharynx initiates peristalsis and the food moves through the UES.
- Esophageal phase (involuntary): now that the food is inside the ESO, the swallowing reflex will initiate [primary peristaltic waves]. If those do not clear it, then it wil move via [secondary peristaltic waves] initate by th ENS caused by distention of the ESO.
The pharynx and the first 1/3 of the esophagus is comprised of what type of muscle?
How about the later 2/3 of the esophagus?
- skeletal muscle
- smooth muscle
During what stage are there two types of peristaltic contraction?
Esophageal
After the oral and pharyn phase, the last phase is the esphageal phase, which is involuntary. What is this phase controlled by? (2)
- Swallowing reflex (primary peristaltic contractions)
- ENS (secondary peristaltic contractions)
Primary peristaltic wave: what is it, what is it controlled by, cannot it occur after a vagotomy. Why or why not?
- The primary peristaltic wave is a continuation of the pharyngeal peristalsis.
- Controlled by: medulla
- Cannot occur after a vagotomy because afferent sensory information from the Vagus nerve is needed for the swallowing reflex to occur.
Secondary peristaltic wave: what is it, what is it controlled by, when does it occur and can it occur after a vagotomy?
- Secondary peristalitic wave will occur if the primary peristaltic wave fails.
- Controlled by: medulla and ENS
- Can occur with or without the oral and pharyngeal phases
- CAN occur after a vagotomy, because controlled by ENS.
The involuntary swallowing reflex is controlled by the _______
medulla
The involuntary swallowing reflex is controlled by the medulla.
What are the steps in the reflex: Starting with food in the pharynx and ending with efferent input to pharynx?
- Food in pharynx
- Somatosensory receptors located near the pharynx, detect the afferent sensory informttion (food in mouth)
- Vagus/glosspharyngeal N. both send sensory information –> swallowing center.
- Swallowing center–> sends efferent info to pharynx to initiate swalling reflex :)
. We can see as the food bolus passes down the esophagus the pressure at that level markedly ________.
increases
Here we can see various pressures in the esophagus at different levels. We can see as the food bolus passes down the esophagus the pressure at that level markedly increases.
Interestingly, the pressure of the LES _________ (why) before the food bolus arrives in the segment above it.
- Pressure of the LES will decrease, indicating that the sphincter is relaxing: Vasoactive intestinal peptide (VIP) is released by the vagus n, causing the smooth muscle in the LES to relax.
What is “receptive relaxation”?
At the same time that the LES relaxes, the top (orad) portion of the stomach relaxes as well to accommodate food.
During swallowing there are changes in pressure along the esophagus as the food bolus passes through it.
What is the main difference between throacic pressure and sphincter pressure?
- The thoracic pressure would be sub-atmospheric (below 0), cause they are normally relaxed. When food passes, pressure increases d/t constriction.
- The sphincter pressure (UES, LES, fundus) would be above 0 because they are normally constricted (closed). When food passes, pressure decreases d/t relaxation.
draw the mono whatever for the UES, 1 part of the pharynx, LES and fundus of the stomach.
Two problems with the location of the intrathoracic esophagus:
- keeping air out of the upper end of the esophagus.
- keeping acid out of the lower end.
How are these problems solved?
UES/LES are closed except when food is passing through :)
What is achalasia?
What happens?
Achalasia- When you swallow, the LES does not fully relax.
What happens:
- Peristalsis is impaired
- LES says closed during swallowing, causing food to back up.
- Increases LES resting pressure (V tight)
Why does achalasia happen?
- Lack of VIP
- ENS was KO’d
- Damage to nerves in the ESO, preventing it from squeezing food into stomach.
achalasia can result in
- Regurgitation
- Dysphagia- difficulty swallowing liquids and solids
- chest pain
Draw mono with achalasia and GERD
Achalasia (orange): LES pressure is set higher; when bolus reaches, it does not go to 0 bc does not relax
How do GERD and achalasia differ?
GERD is much the opposite of achalasia in that it is a RELAXATION of the LES (barrier between the esophagus and stomach).
GERD is d/t?
- low pressure in the LES
- intragastric pressure increases (commonly after a big meal)
GERD is when there are changes in the barrier between the esophagus and the stomach (LES weak/relaxes). This occurs due to low pressure in the LES or if intragastric pressure increases.
What are the results from GERD?
Acid, pepsin, bile in the esophagus= heartburn
If this continues for a while, barrett’s esophagus can occur where there is a transition of the cells