GIT - Lecture 3 Flashcards
What is the upper 1/3 of the UES made of?
striated muscle
What is the lower 2/3 of the UES made of?
smooth muscle
The pharyngeal muscle contraction during the deglutition phase causes the ___ of the upper esophageal sphincter.
relaxation
What nerve releases ACh on the cricopharyngeus muscle?
vagus nerve
The vagus nerve is part of what kind of division?
somatic division
During deglutition relaxation, what happens to impulses?
cessation
During deglutition relaxation, muscles ___.
relax
What are the 4 terms that describe the pharyngeal phase?
- involuntary
- rapid
- stereotyped
- temporospatial coordination
What is the duration of the pharyngeal phase?
around 1/5 second
What activity creates a gradient of pressure that moves food down the esophagus through the lower esophageal sphincter?
peristalsis
Where does the body of the esophageal sphincter lay?
within the thoracic cavity
What is the pressure in the esophagus?
negative (-5mmHg to -10 mmHg)
What is the pressure of the pharynx equal to?
atmospheric pressure
What compartment is the stomach in?
intragastric compartment
What is the pressure in the intragastric compartment (and therefore the stomach)?
positive
What would happen if there were no barriers between the upper GIT pressures?
the higher pressure of the intragastric compartment would be sucked into the esophagus and the air within the pharynx would go down to the esophagus
(because they go down to low pressure)
What are the 2 esophageal forces?
- gravity
- peristalsis
What is the importance of gravity during the esophageal phase?
minor, it has only a small effect for liquids
Each time we swallow, a single ___ peristaltic wave is generated.
primary
How many seconds does it take for food to be propagated the length of the esophagus?
8-10 seconds
What reflex is primary peristalsis part of?
deglutition reflexes
How can we move the peristaltic wave down the esophagus when part of it is made up of smooth muscle and another is made up of striated muscle?
peristalsis is driven by different inputs depending on whether we are talking about striated muscle or smooth muscle
What does the deglutition centre send to the top 1/3 of the esophagus (striated muscle)?
vagus somatic fibres
What does the deglutition centre send to the bottom 2/3 of the esophagus (smooth muscle)?
vagus autonomic fibres
What system is being innervated when the deglutition centre sends vagus autonomic fibres to the bottom 2/3 of the esophagus?
parasympathetic system
Where do the autonomic vagal fibres synapse and activate?
synapse: ENS
activate: ENS neurons
What is the wave of activity in the striated muscle of the esophagus?
sequential: proximal -> distal
What is the wave of activity in the smooth muscle of the esophagus?
synchronous: increased latency of activation in distal esophagus
What is latency?
time between onset of stimulation and the response
What would happen to primary peristalsis if we cut the vagal nerve high up in the neck?
there would be no primary peristalsis
What would happen to primary peristalsis if we cut the vagal nerve transthoracically?
primary peristalsis continues
Why can primary peristalsis occur in an absence of vagal autonomic input?
because the distal esophagus has the enteric circuitry necessary for the propagation
The vagus nerve is essential for ___ peristalsis in the proximal esophagus.
initiating
The intact ENS is essential for ___ and ___ peristalsis in the distal esophagus.
continuing, propagating
What happens when the bolus gets stuck in the esophagus?
local distention
What system senses local distention?
enteric nervous system
What is generated when the bolus gets stuck in the esophagus until it has been displaced?
secondary peristaltic waves
What activates the ENS musculature to help move the bolus down the esophagus during secondary peristalsis?
short, local reflexes (enteric reflexes)
What happens to the afferent fibres of the vagus at the level of esophagus when a bolus gets stuck?
it will send a signal to the deglutition centre which can lead to propagation of a wave down the length of the esophagus
What are vagal-vagal reflexes?
a vagal afferent coming from the GIT going up to the central nervous system leading to activation of
a vagal autonomic fibre which is going to come back further enhance what’s already happening at the level of the ENS.
What system is involved in vagal-vagel reflexes?
parasympathetic system
The lower esophageal sphincter is the last ___ cm of the esophagus.
4
Half of the lower esophageal sphincter is above and half is below the ___.
diaphragm
Is there a visible enlargement of circular muscle in the lower esophageal sphincter?
no
Why is it important that the LES is closed at rest?
because then there would be acid from the stomach burning the esophagus
What is the difference in pH between the esophagus and the stomach?
esophagus: 7
stomach: 2
The ability of the LES to act as a sphincter is a property of the ___.
musculature
Does the LES receive signals from the ENS or autonomic nervous system?
no
What keeps the LES closed?
its residual resistance
Is the LES contracted or uncontracted at rest?
contracted
What kind of relaxation does the LES undergo?
neurogenic
What does the local ENS release to activate ENS neurons to relax the LES?
NANC (-) or vagal stimulation
What reflexes is the LES relaxation part of?
deglutition reflexes
What kind of tone is the LES?
myogenic
Relaxation of the LES is initiated during ___ and mediated by ___ efferent fibres releasing ___.
swallowing, vagal, ACh
What does ACh activate when it is released by vagal efferent fibers during relaxation of the LES?
inhibitory enteric neurons
What do inhibitory enteric neurons release?
NANC transmitters
Any increases in pressure of the intragastric will be felt in the ___.
lower esophageal sphincter
What is the pressure in the esophagus that prevents the movement of contents in either direction?
20 mmHg
What happens to intragastric pressure when you bend over?
it increases
What happens if intraabdominal pressure increases?
pressure increases equally on the stomach and the intraabdominal LES
What are the values of the abdominal cavity pressure and LES pressure when the pressure increases by 100 mmHg?
abdominal cavity: +105 mmHg
LES: 120 mmHg
In hiatus hernias, what happens to intraabdominal pressure and LES pressure (if the LES is displaced into the thorax)?
intraabdominal pressure increases but they do not increase LES pressure
The intrathoracic segment of the LES is subject to ___ pressure.
negative
The intraabdominal segment of the LES is subject to ___ pressure.
positive
What does the presence of an intraabdominal segment of the LES allow?
the sphincter to maintain an effective barrier between the stomach and the esophagus
If the intraabdominal pressure is raised, the pressure in the terminal segment of the LES and the intragastric compartment are ___ equally.
raised
What kind of sphincter is the LES?
intrinsic
What is the anti-reflux mechanism of the LES assisted by?
the presence of an intraabdominal segment
What happens to the sphincter is there is an incompetent LES
it fails to close
What causes pyrosis (heartburn)
acid reflux into the esophagus
Why do women in their last trimester often have problems with acid reflux?
because their high levels of progesterone decrease the resistance of the LES
What are the 3 motor functions of the stomach?
- temporary storage
- physical disruption and mixing of contents
- propulsion into duodenum
How much does the stomach store?
1-2 L
Bolus -> semi-liquid consistency =
chyme
What are the 3 main regions of the stomach?
- fundus
- body
- antrum
What is the function of the proximal part of the stomach?
storage
What is the function of the distal part of the stomach?
mixing and propulsion
What kind of walls are found in the upper portion of the stomach?
thin walls
What kind of walls are found in the lower portion of the stomach?
thick walls
What is the stomach wall composed of?
the same four layers as the rest of the GI tract
What does gastric mucosa consist of?
folds called rugae
What kind of cell types are found in the gastric mucosa of the stomach?
epithelial cells in origin
How are the cells of the gastric mucosa of the stomach arranged?
in pits and glands
What does the muscularis externa of the stomach contain an extra layer of? What is it called?
smooth muscle called oblique muscle
What is receptive relaxation?
increase in volume without significant increase in intraluminal pressure
What is receptive relaxation restricted to?
the proximal stomach
What kind of reflex is receptive relaxation?
deglutition reflex
What happens during receptive relaxation?
the deglutition centre send vagal efferents and these excitatory neurons are going to activate inhibitory ENS neurons, which will lead to relaxation in the musculature of the proximal stomach
What would happen if the vagi to the proximal stomach are cut?
receptive relaxation is limited
What happens to intragastric pressure if the vagi to the proximal stomach are cut?
it increases greatly
What further activates the inhibitory neurons?
vagal-vagal reflexes
What happens with the intake of the meal and the stimulation of the deglutition centre?
you have a wave of activation and relaxation that carries the bolus along the upper GIT
What is the transmitter released by the inhibitory enteric neurons activated by the vagus?
NANC
What does local distention activate?
- local reflexes (enteric)
- long reflexes (vago-vagal)
What happens to the proximal stomach before the meal arrives?
it relaxes
What happens when the meal arrives?
further stomach relaxation (stretch)
What reflex does the stretch in the stomach produce?
vago-vagal reflexes
