CHAPTER 15. QUIZ 2. GI Tract Motility and Transit Time

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Questions and Answers

What is the primary function of mixing movements in the GI tract?

To prevent food from entering the nasal passages

To keep the contents of the intestine appropriately and thoroughly mixed (correct)

To produce pressures around 30–200 mm Hg

To move the contents of the intestine along the tract

What prevents food from entering the nasal passages during swallowing?

The tongue

The muscles of the nasopharynx (correct)

The dorsal vagal complex

The epiglottis

What is the purpose of the epiglottis moving upward during swallowing?

To prevent aspiration (correct)

To facilitate the passage of food into the esophagus

To relax the striated muscle of the esophagus

To stimulate the respiratory center

What is the range of pressures produced by the LES?

20–60 mm Hg Signup and view all the answers

What neurotransmitters relax the muscle of the esophagus?

VIP and nitric oxide Signup and view all the answers

What is the function of the dorsal vagal complex in the swallowing process?

To activate efferent fibers that terminate on the enteric nervous system Signup and view all the answers

What is the main function of propulsive movements in the GI tract?

To move the contents of the intestine along the tract Signup and view all the answers

What structure constricts to prevent reflux back into the pharynx during swallowing?

UES Signup and view all the answers

What is the role of the tongue in the swallowing process?

To squeeze and roll food into the posterior pharynx Signup and view all the answers

What inhibits the respiratory center during swallowing?

The act of swallowing Signup and view all the answers

What is the function of the nasopharynx during swallowing?

To prevent food from entering the nasal passages Signup and view all the answers

What type of muscle is contracted by the release of acetylcholine during swallowing?

Striated muscle Signup and view all the answers

What is the primary effect of anatomical abnormalities in the esophagus?

Disruption of the normal pathway of food to the stomach Signup and view all the answers

Which of the following conditions is associated with changes in the luminal pressures of the esophagus?

all are correct Signup and view all the answers

What is the potential consequence of increased luminal pressures in the esophagus?

Reflux of food into the pharynx Signup and view all the answers

Which of the following is an example of a mechanical etiology of esophageal disease?

Hiatal hernia Signup and view all the answers

What is the relationship between anatomical, mechanical, and neurologic etiologies of esophageal diseases?

They often overlap Signup and view all the answers

What is the primary effect of uncoordinated muscle contractions in the esophagus?

Difficulty in moving food downward Signup and view all the answers

What is the characteristic of a hypertensive LES?

Mean pressure of 45 mm Hg or higher Signup and view all the answers

What is the result of the inability of the esophagus to relax properly for food travel?

Dysphagia, regurgitation, and significant pain Signup and view all the answers

What is the effect of neurologic disorders on the esophagus?

Disruption of nerve pathways and sensing Signup and view all the answers

What is the common result of mechanical etiologies, such as achalasia and diffuse esophageal spasm?

Dysphagia Signup and view all the answers

What is the characteristic of muscle contractions in diffuse esophageal spasm?

Uncoordinated and irregular Signup and view all the answers

What is the pressure threshold for defining a hypertensive LES?

45 mm Hg Signup and view all the answers

What is the common symptom of both achalasia and hypertensive LES?

Dysphagia Signup and view all the answers

What is the primary purpose of an esophageal manometry study?

To evaluate changes in pressure in the esophagus at various levels Signup and view all the answers

Which type of study is best suited for evaluating questionable anatomical abnormalities in the esophagus?

Upper GI series with ingested barium Signup and view all the answers

What is recorded first during an esophageal manometry study?

The pressure of the LES Signup and view all the answers

What is evaluated during the withdrawal of the catheter in an esophageal manometry study?

The pressure of the esophagus at different levels Signup and view all the answers

During which state does the migrating motor complex occur?

During fasting Signup and view all the answers

What is the primary function of the migrating motor complex?

To move residual undigested food through the GI tract and bacteria from the small intestine to the large intestine Signup and view all the answers

What is the duration of the migrating motor complex cycle?

45-180 minutes Signup and view all the answers

Which phase of the migrating motor complex is characterized by peak electrical and mechanical activity?

Phase III Signup and view all the answers

What triggers the migrating motor complex?

Vagal stimulation releasing motilin Signup and view all the answers

What triggers the release of motilin, leading to the migrating motor complex?

Vagal stimulation Signup and view all the answers

What is the characteristic of phase III of the migrating motor complex?

Peak electrical and mechanical activity Signup and view all the answers

What interrupts the migrating motor complex?

Feeding Signup and view all the answers

What is the effect of feeding on the migrating motor complex?

It interrupts the migrating motor complex Signup and view all the answers

What is the origin of the waves of electrical activity in the migrating motor complex?

The stomach Signup and view all the answers

What is the main purpose of the stomach's motility?

To break down food into small particles and mix it with digestive juices Signup and view all the answers

Which nerve stimulates the stomach to increase the number and force of contractions?

Vagus nerve Signup and view all the answers

What is the effect of duodenal distention on the stomach's motility?

It decreases the gastric tone to slow emptying Signup and view all the answers

Which hormone increases the strength and frequency of contractions in the stomach?

Gastrin Signup and view all the answers

What is the effect of increased fat content in the small intestine on the stomach's motility?

It triggers the release of cholecystokinin to slow emptying Signup and view all the answers

What is the approximate time it takes for solids to empty from the stomach?

3-4 hours Signup and view all the answers

What can increase the incidence of gastroesophageal reflux disease?

Gastric motility disorders that slow emptying Signup and view all the answers

What is a common effect of vasoactive drugs on gastric motility?

increase catecholamine concentrations and decreased motility Signup and view all the answers

Which of the following conditions can decrease gastric motility?

Hyperglycemia Signup and view all the answers

What is the purpose of using drugs like erythromycin and metoclopramide in patients with gastric motility disorders?

To increase gastric motility Signup and view all the answers

What type of patients are often given vasoactive drugs that can decrease gastric motility?

Critically ill patients Signup and view all the answers

What is the primary function of the small intestine?

To circulate the contents and expose them to the mucosal wall Signup and view all the answers

What is the purpose of using a radiotracer in a gastric emptying study?

To track the movement of the ingested meal Signup and view all the answers

What is the duration of the gastric emptying study?

60 to 120 minutes Signup and view all the answers

What is a limitation of gastric emptying scintigraphy?

It is affected by multiple factors including meal composition and data acquisition parameters Signup and view all the answers

What is the purpose of the gastric emptying study?

To evaluate the function of the stomach Signup and view all the answers

gastric motility studies can be paired with which study?

small intestinal motility Signup and view all the answers

What is the primary function of segmentation in the intestine?

To allow the contents to remain in the intestine long enough for absorption Signup and view all the answers

How do the circular and longitudinal muscle layers work to achieve segmentation?

They work in a coordinated fashion to achieve segmentation Signup and view all the answers

What system controls segmentation in the intestine?

The enteric nervous system Signup and view all the answers

What is the result of the process of segmentation in the intestine?

The contents of the intestine are divided into smaller segments Signup and view all the answers

What happens to the isolated segments of intestine after segmentation?

They are further divided into smaller segments Signup and view all the answers

What is the primary cause of muscle dysfunction in the small intestine due to mechanical obstruction?

The physical blockage that prevents muscle contraction Signup and view all the answers

What is the typical concentration of bacteria in the small intestine?

Fewer than 100,000 organisms per milliliter Signup and view all the answers

What is the result of bacterial overgrowth in the small intestine?

Alterations in absorptive function leading to diarrhea Signup and view all the answers

How are reversible causes of small bowel dysmotility, such as bacterial overgrowth, typically treated?

Antibiotics to eliminate the bacterial overgrowth Signup and view all the answers

What is another reversible cause of small bowel dysmotility, besides mechanical obstruction and bacterial overgrowth?

All of the above Signup and view all the answers

What is the main reason for decreased nutrient absorption in patients with IBD?

Structural abnormalities in the mucosa Signup and view all the answers

What is the primary consequence of short bowel syndrome?

Diarrhea, malnutrition, and weight loss due to insufficient functional compensation Signup and view all the answers

Which type of abnormality is associated with scleroderma and connective tissue disorders?

Structural abnormality in the intestinal smooth muscle Signup and view all the answers

What is the primary symptom of neuropathic alterations in the small intestine?

Bloating, nausea, vomiting, and abdominal pain Signup and view all the answers

What is the result of small intestinal dysmotility?

Malnutrition due to decreased nutrient absorption Signup and view all the answers

What is the primary use of small bowel manometry in patients?

Evaluating patients with unexplained nausea, vomiting, and abdominal pain Signup and view all the answers

How long is the recording time for the fasting period in a small bowel manometry study?

4 hours Signup and view all the answers

What is the characteristic of a myopathic result in small bowel manometry?

Phase III exhibits very low amplitudes Signup and view all the answers

What is the percentage of patients with unexplained symptoms in which small bowel manometry results in a change of diagnosis?

8-15% Signup and view all the answers

What is the purpose of the small bowel manometry study?

To evaluate the contractions of the small intestine Signup and view all the answers

What is the characteristic of a neuropathic result in small bowel manometry?

Uncoordinated contractions or inappropriate postprandial response Signup and view all the answers

What is the primary function of the giant migrating complexes in the large intestine?

To produce mass movements across the large intestine Signup and view all the answers

What is the result of rectal distention, VIP, and NO release in the large intestine?

Promotion of the urge to defecate Signup and view all the answers

What is the effect of distention of the ileum on the ileocecal valve?

It relaxes the valve Signup and view all the answers

What is the frequency of the giant migrating complexes in a healthy individual per 24 hours?

What is the average amplitude of the giant migrating complexes in the large intestine?

115 mm Hg Signup and view all the answers

What is the origin of the giant migrating complexes that produce the urge to defecate?

Sigmoid colon Signup and view all the answers

What are the two primary symptoms of colonic dysmotility?

Altered bowel habits and intermittent abdominal cramping Signup and view all the answers

Which of the following conditions is associated with a decrease in the amplitude and frequency of giant migrating complexes?

Irritable bowel syndrome (IBS) with constipation Signup and view all the answers

What is the effect of stress on the colon in individuals with IBS?

It causes motor dysfunction and visceral hypersensitivity Signup and view all the answers

What is the characteristic of Rome II criteria for diagnosing IBS?

Abdominal pain/discomfort plus at least two of three features Signup and view all the answers

What is the effect of inflamed mucosa in the colon in IBD?

It suppresses the mixing and propulsive movements and tonic contractions Signup and view all the answers

What is the primary function of giant migrating complexes in the large intestine?

To regulate bowel habits Signup and view all the answers

What is the purpose of a lower GI series in evaluating colonic motility?

To detect anatomical abnormalities in the colon and rectum Signup and view all the answers

What type of patients undergo studies evaluating giant migrating complexes?

Patients with known diagnoses of IBS and IBD Signup and view all the answers

What is the role of barium in a lower GI series?

To outline the intestine and allow for detection of anatomical abnormalities Signup and view all the answers

What is the primary goal of evaluating colonic motility in patients with IBS and IBD?

To understand the physiology and mechanism causing the condition Signup and view all the answers

Study Notes

There are two primary movements within and along the GI tract: mixing movements and propulsive movements.
Mixing movements keep the contents of the intestine appropriately and thoroughly mixed, while propulsive movements, consisting of periodic contractions of certain GI tract segments (peristalsis), move the contents of the intestine along the tract.
Transit through the esophagus starts with swallowing, which begins with the oropharynx pushing food backward and downward while the muscles of the nasopharynx prevent food from entering the nasal passages.
The epiglottis moves upward in a protective mechanism over the larynx and trachea to prevent aspiration.
The act of swallowing inhibits the respiratory center to protect from aspiration, but it is so short-lived it is unnoticeable.
Food enters the esophagus through the UES, which then constricts to prevent reflux back into the pharynx, producing pressures around 30–200 mm Hg.
Two waves of peristalsis move the food into the stomach through the LES, which also produces pressures between 20 and 60 mm Hg.
Afferent nerve fibers transmit to the dorsal vagal complex, activating efferent fibers that terminate either on the striated muscle of the esophagus or on the nerves of the enteric nervous system.
Release of acetylcholine contracts the muscle, while VIP and nitric oxide (NO) relax it.
Diseases of the esophagus can be grouped into anatomical, mechanical, and neurologic etiologies, although many disease states involve overlap between two or all three.
Anatomical etiologies include the presence of diverticula, hiatal hernia, and changes associated with chronic acid reflux.
Mechanical etiologies include achalasia, diffuse esophageal spasm, and hypertensive LES.
Neurologic disorders such as stroke, vagotomy, or hormone deficiencies can alter the nerve pathways, disrupting the appropriate sensing and feedback.
In achalasia, the smooth muscles are unable to relax and move food down, and the increased tone of the LES does not allow for complete relaxation, resulting in dysphagia, regurgitation, and significant pain.
In diffuse esophageal spasm, muscle contractions are uncoordinated, resulting in food not properly moving downward.
A hypertensive LES is defined as an LES with a mean pressure of 45 mm Hg or higher, leading to dysphagia and chest pain.
In evaluating esophageal function, it is important to select a study with an appropriate clinical correlation—is it a problem with motility or is it an anatomical abnormality?
Esophageal manometry studies detect changes in pressure in the esophagus at various levels and evaluate esophageal motor function between swallows.
Upper GI series and ingested barium evaluate the act of swallowing and visualize the lining of the esophagus for anatomic abnormalities.
The migrating motor complex (MMC) occurs only during fasting, and is composed of waves of electrical activity in regular cycles originating in the stomach and terminating in the distal ileum.
Vagal stimulation releases motilin, which triggers an MMC leading to peristaltic waves that occur every 45 to 180 minutes and are composed of four phases.
The MMC is significant because it moves residual undigested food through the GI tract and also moves bacteria from the small intestine to the large intestine.
The stomach is a J-shaped sac that serves as a reservoir for large volumes of food, mixes and breaks down food to form chyme, and slows emptying into the small intestine.
Solids must be broken down into 1 to 2 mm particles before entering the duodenum, and they take approximately 3 to 4 hours to empty from the stomach.
Liquids empty faster than solids.
The motility of the stomach is controlled by intrinsic and extrinsic neural regulation, including parasympathetic stimulation to the vagus nerve, sympathetic stimulation via the splanchnic nerve, and intrinsic nervous system coordination.
Neurohormonal control is also at play, with gastrin and motilin increasing the strength and frequency of contractions, and gastric inhibitory peptide inhibiting them.
Emptying of the stomach is controlled by neural and hormonal mechanisms as well as the composition of ingested food.

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Description

Test your understanding of the mixing and propulsive movements within the gastrointestinal tract, including peristalsis and swallowing. Learn how these mechanisms work together to facilitate transit through the esophagus and intestine.