Gastrointestinal Physiology: Motility I Flashcards
The only exception to the net mouth to anus (aboral) movement
Vomiting
Generate the force to move material along the GI tract
Phasic contractions
Create resistance to movement
-normally in the sphincters or pathologically elsewhere
Tonic contractions
What are the three primary functions of mastication?
- ) Reduction in particle size
- ) Mixing
- ) Enhance stimulation of taste buds and other receptors
Mixing of the food with saliva is needed to libricate the mass and increase the exposure to which two things?
- ) Salivary amylase (carbohydrate digestion)
2. ) Lingual lipase (lipid digestion)
Mastication enhances stimulation of taste buds and other receptors in the oral cavity to increase salivation and appreciation of the food. Some of these receptors initiate the
Cephalic phase of digestion
Control of mastication is primarily
Reflexive
Plays a much larger role in indigestion than most people realize
Impaired chewing
Moving food and liquid from the mouth into the stomach, is an example of integration within the neural system. This is referred to as
Swallowing
Swallowing is divided into which 3 phases?
- ) Oral
- ) Pharyngeal
- ) Esophageal
When not swallowing (i.e. at rest), the upper esophageal sphincter (UES) and the lower esophageal sphincter (LES) are
Contracted
-effectively isolates the esophagus
The esophageal muscles do not maintain any tonic contractions, thus the esophagus is
Flaccid
The pressures in the upper and lower esophagus reflect the pressure in the
Thoracic and abdominal cavities respectively
The buccal or oral phase of swallowing is under
Voluntary control
A bolus, approx. 5-15 cm3, is moved to the back of the mouth by elevating the front of the tongue against the surface of the hard palate in the
Buccal (oral) phase
In the buccal (oral) phase of swallowing, the bolus is moved into the oropharynx by
Retraction and depression of the tongue
The driving force for movement of the bolus in the buccal phase is a pressure gradient of approximately
4-10 mmHg
An involuntary reflex coupled to the primary esophageal peristaltic wave
Pharyngeal phase of swallowing
Pharyngeal phase is an involuntary reflex coupled to the primary esophageal peristaltic wave. Both are controlled by the
Swallowing center
The pharyngeal phase is initiated by the bolus touching the pillars of fauces, tonsils, soft palate, base of tongue and
Posterior wall of the pharynx
When this happens, afferent impulses go to the swallowing center. Efferent fibers convey impulses back to the
Pharyngeal muscles, UES, esophageal muscles, LES, and orad portion of the stomach
The swallowing center also interacts with other centers controlling
Respiration and speech
Relaxes as the pharyngeal peristaltic wave starts (pressure gradient up to 100 mm Hg), and the bolus is propelled into the esophagus
UES
At the end of the pharyngeal contraction, the UES contracts to a level above resting tone. This prevents
Reflux
The air passages close simultaneously with the onset of the
Pharyngeal wave
The soft palate presses against the posterior pharyngeal wall sealing the
Nasopharynx
In the pharyngeal phase, the vocal cords come together, the epiglottis deflects horizontally and the larynx moves forward and upward under the base of the tongue closing the
Larynx
A primary peristaltic wave is initiated by the swallowing center, and mediated by the vagus to the striated circular and longitudinal muscles in the
Esophageal phase
This peristaltic wave goes to the myenteric plexus in the smooth muscle, thus, activating the
Enteric System
The primary peristaltic wave starts just below the sphincter and spreads downwards pushing the bolus toward the stomach when the
UES pressure is high
Almost simultaneously, a wave of inhibition starts in the
Proximal LES (LES relaxes)
The likely neurotransmitters for this LES inhibition are
VIP and NO
This continues into the stomach (receptive
relaxation), and is mediated by
Vagal inhibitory fibers acting on ENS
The temporary inhibition of resting tone in the fundus and orad area
Receptive Relaxation
This maintains the esophageal-gastric pressure gradient to prevent
Reflux during swallowing
After the peristaltic wave passes the LES, the LES contracts to a level above resting tone. This is mediated by
-prevents reflux
ACh and enkephalins
May move through the LES before the peristaltic wave in response to gravity
Liquids
Air in the pharynx at the start of a swallow passes into the
Trachea
Air trapped in saliva and food, or voluntarily swallowed, passes into the stomach. This results in
Burping
A peristaltic wave not preceded by pharyngeal activity or relaxation of the UES
Secondary Peristalsis
Functions to clear the esophagus of retained food and/or refluxed gastric contents
Secondary peristalsis
Initiated by distention in the body of the esophagus that stimulates stretch receptors in the wall
Secondary peristalsis
What is secondary peristalsis mediated by in
- ) Striated muscle?
- ) Smooth muscle
- ) Vagus
2. ) Vagus and ENS
Is there any sensation associated with secondary peristaltic contractions?
No (little to none)
Normally maintains a pressure that is 20-40 mmHg higher than the stomach which prevents reflux
LES
This anti-reflux mechanism is particularly important during the third-trimester pregnancy as other mechanisms are weakened
Secondary peristalsis
Another anti-reflux mechanism is the pinching action of the diaphragm on the
Esophagus
Infants rely primarily on this anti-reflux mechanism, while awaiting other mechanisms to develop
Pinching of diaphragm on esophagus
Another anti-reflux mechanism is that increases in intra-gastric and intra abdominal pressures lead to increased
LES pressure
Occur in humans and are centrally controlled (does not occur in rats)
Retching and Vomiting
However, reverse esophageal peristalsis does not usually occur in
Humans
Starts with orally directed peristalsis in the small intestine that leads to movement of intestinal
contents into the stomach
Retching and Vomiting
Then forceful contractions of duodenal and gastric antral muscles, coupled with deep inspiration and decreased LES tone leads to
Retching
Movement of contents into the esophagus but with inadequate force to move contents through UES
Retching
Subsequent additional contraction of the\ diaphragm and abdominal muscles (increases intraabdominal pressure), coupled with further decreases in LES and UES tone leads to
Vomiting
Storage in the stomach is accomplished by both
- ) Receptive relaxation
2. ) Accommodation
Muscle relaxation in response to stretching or distension by food
Accommodation
Gastric filling leads to changes in volume with little to no change in
Wall pressure
Increasing gastric volume with 1.6L of air increases intragastric pressure by
10mmHG or less
Allows digestion of foo by salivary and gastric enzymes, as well as controlled gastric emptying
Gastric storage
The storage site in the stomach
Upper stomach
Causes the mixing of food, salivary secretions and gastric secretions
Antral muscle contraction
Mixing facilitates gastric
Digestion
The antrum grinds the solid food into small particles which the pylorus allows to pass into the
Duodenum
The rate of gastric emptying is controlled to deliver chyme to the small intestine for optimized
Digestion and absorption
Sweep luminal contents (e.g. undigestible materials) out of the stomach, down through the small intestine and into the large intestine
Migrating Myoelectric Complexes (MMCs)
MMCs are only active during the
Interdigestive period
At the onset of eating, shallow and slow peristaltic contractions start over the corpus, and increase in strength and velocity as they move into the
Antrum
With increased time after eating, contractions start higher up in the corpus and are
Stronger
The simultaneous contraction of the terminal antrum and pylorus
Antral Systole
Results in 1) retrograde movement of chyme back into the stomach, leading to effective mixing, and 2) shearing forces, which reduces particle size
Antral systole
Leave the stomach prior to antral systole
Chyme and liquids
During the interdigestive period, when the stomach and small intestine empty, they generate
Strong peristaltic waves (MMCs)
Results in semi-liquid chyme or liquids passing through the pylorus prior to antral systole and closure of pyloric sphincter
Gastric Emptying
The emptying rate is controlled by the interactions of gastric and duodenal motilities, and pyloric sphincter tone, which are modified by
Enteric, spinal, and vago-vagal reflexes and GI peptides
Increased gastric volume increases gastric emptying rate via
Gastric stretch receptors
Particle size: 0.25 mm3 empty faster than 10 mm3 due to the
Pyloric lumenal diameter
What empties faster, carbohydrates or proteins?
Carbohydrates
What empties faster, proteins or fats?
Proteins
Duodenal chemo-receptors, CCK, GIP and secretin, all have what effect on the rate of gastric emptying?
Decrease rate
What empties faster, acidic or neutral species?
Neutral
What empties faster, hypotonic, isotonic, or hypertonic solutions?
Isotonic faster than hypotonic
Hypotonic faster than hypertonic
The duodenogastric reflex i.e. excessive duodenal distention activates duodenal stretch receptors, leading to
Reduced gastric contraction and emptying rate
Ileal distension decreases
Gastric emptying
Functions in gastric and small intestine interdigestive motility
Migrating myoelectric complex (MMC)
The strongest peristaltic contractions observed in healthy individuals are from
MMCs
“Clean out” residual material from the stomach and small intestine and moves it into the large intestine
MMCs
MMCs require an intact
Enteric nervous system
The beginning of the MMC is associated with rising blood levels of
Motilin
Stop with rising blood gastrin levels and feeding
MMCs
Not related to ‘hunger pangs’ but could contribute to the discomfort and pain of ulcers
MMCs
Slow movement of the chyme through the intestine maximizes
Absorption of nutrients
Mixing in the small intestine facilitates intraluminal digestion by mixing chyme with secretions and facilitates absorption by increasing exposure of the chyme to the
Epithelial surface
In the small intestine, functions to empty unabsorbed residue and secreted material into the large bowel
MMCs
Muscularis mucosae and villus muscle activity is responsible for movement of the
Mucosa and Villi of small intestine
Muscularis mucosae and villus muscle contractions are independent of contractions in the
Muscularis externa
Activity in these muscles serves to increase absorption and aids
Lymph flow
Sympathetic stimulation and chyme stimulating touch receptors on the epithelial surface of the small intestine induces
Rapid shifts in mucosal surface
This can be seen in X-rays after administering
Barium salts
Responsible for intraluminal mixing and propulsion
Muscularis externa
