L26 Flashcards
what is esophageal manometry
This is a technique where you put a pressure sensing catheter into various parts of the GI tract and then when it contracts the pressure increases and if is sensed by the receptor
This allows for identification of defects in the process by looking for weird pressure contraction relationships in the tract
what is the function of chewing
- mechanical digestion - ingestion
- mixing food with saliva = tasting and start of chemical digestion. it also stimulates olfactory components therefore
- stimulus for cephalic phase
how is chewing controlled
• voluntary - skeletal muscle and involuntary reflex in the brainstem
- initiation – bolus in mouth
- stimulation of taste centers – rhythm (coordinates the process of swallowing)
- strength – consistency of bolus
what is the definition of swallowing
rapid transfer of food from the mouth to stomach
why is swallowing a complex process
Converts mouth and pharynx pathway from gas
transfer function to food transfer function
Prevention of reflux
what processes are involved in swallowing
- Oral events
- Initiation of swallowing reflex
- Cascade of sequential events in
- Pharynx
- esophagous
what is the swallowing reflex
The uvula is part of the stoft pellet and that is what gets pushed up so food doesn’t go into the nasopharynx
Epiglottis does down when swallowing when you are not swallowing it is closed so that acid doesn’t get into the respiratory tract
Open = relax
As food gets pushed down the esophagus then the lower esophageal sphincter open do food can get into the stomach
Peristalsis is also happening at this time. It starts at the skeletal muscle all the way down the esophagus and into the smooth muscle. This wave will last about 9-10 sec and the lower esophageal sphincter will be open for the entire period of this time
in swallowing, what events are under voluntary control
• Oral events are under voluntary control (we decide when to
initiate a swallow)
• Voluntary events activate stretch receptors that activate an involuntary response (i.e. a reflex)
in swallowing what events are under involuntary control
- Swallowing reflex which is caused by the Swallowing center in brainstem response to stretch
- Pharyngeal muscles. this is a Striated muscle controlled directly by swallowing center
• Esophageal muscle = Striated muscles controlled directly by swallowing center
it also consists of Smooth muscle controlled by The Enteric Nervous System which is Modulated/co-ordinated by the
swallowing center
what kind of muscles are the pharyngeal muscles
they are all striated
The cascade started by voluntary control (oral) causes activation of involuntary control which are all coordinated by the swallowing centre in the brainstem which responds to stretch
There is a very specific transition zone where the muscle type transitions from skeletal to smooth
4
what happens when the food arrives in the esophagus
it initiates a primary peristaltic wave which sweeps food down esophagus towards stomach
• If food not cleared from esophagus by primary peristaltic wave a Secondary peristaltic wave is initiated. this process is repeated until food cleared (so you don’t choke)
what does Relaxation of lower esophageal sphincter allow for
Relaxation of lower esophageal sphincter allows passage of food from the esophagus to the stomach
when swallowing what happens at the level of the stomach
• Relaxation of proximal stomach. this is called Receptive relaxation which reduces stomach pressure below esophageal pressure to limit gastric reflux
this is a storage mechanism but is also part of the swallowing reflex
describe the timing of the upper and lower esophageal sphincters in swallowing
At the initiation of swallowing then the upper esophageal sphincter opens
At the esophagogastric junction, which the lower esophageal sphincter is apart of, that the lower esophageal sphincter relaxes and depressurized at the same point that the upper esophageal sphincter opens
Therefore the lower esophageal sphincter stays open the entire time of the peristaltic wave
when is pressure in the esophagus highest
when swallowing
what are some causes of acid reflux
Abnormal relaxation of lower esophageal
sphincter
• Lack of Receptive Relaxation or gastric
accommodation in the stomach
- Conditions that increase gastric pressure
- Excessive gastric secretion
- Infection with H. pylori
what are treatments for heartburn
Antacids (neutralize gastric HCl)
• Antihistamines & proton pump inhibitors
(stop HCl production)
- Lifestyle modifications (E.g. diet) eat smaller meals
- Surgery (depends on cause) there would have to be an anatomical cause
what is the role of the Upper Esophageal Sphincter
- Additional barrier to reflux
* Prevents air entering esophagus
the Lower Esophageal Sphincters zone of high pressure is what
- 3-5 cm zone of high pressure
* 12-30 mmHg greater than gastric pressure
what does the lower esophageal sphincter respond to
• Responds to changes in gastric pressure
• Acts with other structures e.g. diaphragm
(Esophageal/Gastric junction : EGJ)
what are the functions of the stomach
Storage functions maintain pressure as volume increases
- Receptive relaxation
• Reduction of gastric tone with swallowing
- Gastric accommodation
• Reflex relaxation of proximal stomach with
gastric distention
what are the 3 main types of gastric motility
storage
retropulsion
controlled delivery to the duodenum
there are 3 main types of gastric motility
describe the storage function
Allowing food entry during swallowing
Accommodating increased volume during a meal
there are 3 main types of gastric motility
describe the retropulsion function
Combines peristaltic contraction (pushes food forward) and pyloric sphincter contraction (pushes
food back)
therefore it has a mixing function
there are 3 main types of gastric motility
describe the delivery function
Changing contraction/ relaxation of the pyloric
sphincter
It is initially closed – allows mixing to occur
it has short periods of opening which allows the entry of food to match capacity (volume and secretion rate)
describe the functional anatomy of the stomach
Proximal stomach
= Fundus, proximal body. this is the Site of storage
Transitional area = Mid body
Distal stomach = Distal body, Pylorus. is responsible for Movement, Mechanical breakdown and Controlled release
what is the function of the proximal region of the stomach
The proximal parts ( the fundus and the cardia (fist part cyme will enter) is for storage.
This is where you have active modulations of the muscle tone of the stomach during swallowing so that you can maintain the pressure gradient needed for swallowing
what is the function of the distal region of the stomach
The distal body and the pylorus is the parts involved in the retropulsion, movement of cyme, controlled release to the duodenum and mechanical and chemical digestion
what is the vago/vagal reflex
when accommodation of the stomach is initiated by the
long reflex loop from the CNS. (the vagal nerve)
when does peristalsis start
phasic peristaltic contractions occur 5-10 min after the arrival of food in the stomach
what is the results of peristatic contractions
• Spread from greater curvature towards the pylorus
describe the timing of peristalsis
begins 5 -10 min after food arrives
• 0 – 60 minutes of gentle ripples
• 60 – 300 minutes increasing intensity
what is peristalsis coordinated by
the pyloric sphincter
when it is closed = Mechanical breakdown (retropulsion)
open = controlled delivery to duodenum
the duration and intensity of peristalsis depends on
Consistency and composition of food
• Particulate vs homogenized food
- Fat content
- Related to gastric emptying
when does retropulsion occur
retropulsion is depending on peristaltic waves in the stomach therefore it starts at the same time as peristalsis (5-10 min after the arrival of food)
when does reteropulsion occur
Happens when the pyloric sphincter contracts at the same time as peristaltic contractions occur
• Results in a backwards (retrograde) flow of content
toward the fundus.
what is the function of retropulsion
Mixes gastric contents with secretions to produce chyme
Mechanically reduce size of food particles by….
• rebounding wave of retropulsion
• sieve effect of pyloric sphincter
what is retropulsion regulated/controlled by
the gastric phase
Chemical and Stretch receptors
initiate in response to stomach contents
Frequency of contraction doesn’t change (for a given section of GI tract)
Force of contraction depends on the amount of time of each wave is above threshold.
• Frequency determined by slow waves ≈ 3 min
y
what are the different phases regulated
- The GI tract has different functions
at different phases of digestion. - The regulation of the GI tract changes to facilitate these different
functions.
Phases are not absolute but overlap!
Regulation of motility and the rate of gastric emptying changes by phase. how is theis achieved
by modulation of motility in proximal and distal stomach
what happens during the cephalic and gastric phase
• Proximal stomach relaxed (storage)
• Pyloric sphincter closed
• Distal motility increased but most material returns to proximal region
(retropulsion)
Therefore cyme is released to the more distal areas for breakdown
what happens during the intestinal phase
• Tone of muscle in proximal region increased
• Pyloric sphincter opens more frequently (controlled release to the duodenum)
• Antral contractions results in passage of material from stomach to duodenum
• Duodenal contractions are coordinated with stomach and inhibited as chyme is
released into the duodenum.
Pushing cyme away from the proximal regions of the stomach and end the storage function so that you relases more chyme into the intestine
what is the Cephalic Phase
• Prepares stomach for the arrival of food
• In response to the presence of food in the mouth, chewing and swallowing the
CNS
how does the cephalic phase inhibit muscles in the body of the stomach
by modulating the ENS
this is what causes receptive relaxation and accommodation which are storage functions
what do low level stimulation of antral contractions by modulation of ENS to
Activate muscular contractions in preparation for food (increases the amplitude of contraction)
Stimulate the release of gastrin from G Cells
• Has an important role in the regulation of gastric secretion
the gastric phase is mediated by receptors in the stomach wall. what are these receptors and what do they respond to
Mechanoreceptors respond to distention of stomach wall by food
Chemoreceptors response to presence of products of digestion
• Amino acids and short peptides
during the gastric phase, when the receptors in the stomach wall are activated, what happens
• Intrinsic reflexes involving ENS
• Extrinsic reflexes
- eg Vago/vagal reflexes which Mediate activity of ENS
what do the reflexes in the gastric phase do
Inhibit tone in proximal stomach to accommodate food. this is called gastric accommodation
Stimulate contraction in distal stomach through release of Acetylcholine and substance P. this also happens when stimulation of G cells to release gastrin
what is able to stimulate contraction of the distal stomach during the gastric phase
Stimulate contraction in distal stomach through release of Acetylcholine and substance P. this also happens when stimulation of G cells to release gastrin
is the pyloric sphincter open or closed during the cephalic and gastric phase
yes
what is the main functions of the intestinal phase
controlled delivery of food from the stomach to the duodenum
Ensures food is processed correctly in stomach
Matches delivery of food to small intestine to its ability to handle the food
• E.g. duodenal enzyme and bicarbonate release
• Related to physical / chemical properties of food
during the intestinal phase how does the body match the delivery of food to small intestine to its ability to handle the food
- E.g. duodenal enzyme and bicarbonate release
* Related to physical / chemical properties of food
what is happening the the pyloric sphincter during the intestinal phase
Pyloric sphincter open more during peristaltic wave (depending on rate of
release)
what is happening in the duodenum during the intestinal phase (to do with contraction)
• Duodenal contractions inhibited
what impacts the speed of gastric emptying into the duodenum
Size of meal
• Larger is faster
• Stretching of stomach wall (mechanoreceptors)
Composition of meal
• Energy content of meal, higher energy (e.g. fat) is slower
• Liquid meals delivered to SI faster than solid
• Osmolarity, isosmotic faster than hyperosmotic or hypo-osmotic
Rate of delivery of chyme into the
duodenum by negative feedback
inhibition of gastric muscle. If you are wanting to slow down the relase to the duodenum you also want to increase the activation of the sphincter so that it is closed more than i is open
Distal stomach – Peristalsis
(for controlled delivery)
Adrenaline and NOS decreases
(Acetylcholine can increase)
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what happens in the duodenum
Delivers digestive enzymes from the pancreas. Neutralises acid to make food safe for intestinal epithelia - allowing contact digestion and absorption
This is the site where pancreatic enzymes, bicarbonate and bile are released into the cyme. This is important as we need to neutralise the acid so that you dont damage the intestinal epithelial cells
why is Initially delivery to the duodenum is limited
Ensures effective gastric digestion
this is regulated by the Contracted pyloric sphincter
At the start of the intestinal phase – chyme
moves from the stomach to match capacity
of duodenum
Tonic proximal stomach contraction
Phasic distal stomach contraction
Controlled inhibition of the pyloric sphincter
(periodically lets chyme through)
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what is the most common fed motility pattern
segmentation
what is another name for fed state
postprandial
what muscles contract for segmentation
• Circular muscle contraction in segments
how does segmentation aid in digestion
Aids digestion by mixing secretions
Aids contact digestion and absorption by exposing
contents to small intestinal epithelial layer
what is segmentation regulated by
Magnitude of contractions regulated by ENS reflexes (with
input from CNS). Frequency of contraction determined by the
interstitial cells of Cajal (not regulated)
what are the 2 motility patterns of the small intestine
segmentation and peristalsis
describe peristalsis in the small intestine
- Infrequent
- Ascending circular muscle contraction
- Descending circular muscle relaxation
- Longitudinal muscle shortening (contraction)
- Absorption at more distal sites
- Transfer of waste to large intestine
what are the 3 motility pattern of the large intestine
storage
perialstalis (mass movement)
eminination (defecation reflex)
describe the storage motility pattern of the large intestine
5 things
- large intestinal transit is slow (24-48 hrs)
- This inactivity enhances water absorption
- Segmentation (Mixing) occurs during storage
- Short duration contractions – circular muscle
- Turnover of contents aids absorption
describe peristalsis in the large intestine
this is for Mass movements
- high intensity contractions
- propel contents into rectum
describe the elimination motility pattern of the large intestine
this is the defecation reflex which is strong contractions which happen a couple of times per day (when you poop)
describe the deification reflex/elimination motility pattern of the large intestine
(Defecation reflex)
• Relaxation of internal anal sphincter – smooth muscle.
• The rectoanal inhibitory reflex prevents spontaneous opening of
external anal sphincter.
• External anal sphincter is under conscious control - skeletal
muscle – relaxes when defecation is appropriate.
• Valsalva maneuver – closing the airway while exhaling to
increase force for elimination
