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Questions and Answers
Which type of smooth muscle is primarily responsible for the function of sphincters?
Which type of smooth muscle is primarily responsible for the function of sphincters?
What is a primary mechanism that maintains smooth muscle in a partially contracted state?
What is a primary mechanism that maintains smooth muscle in a partially contracted state?
In the gastrointestinal tract, how would the application of norepinephrine or epinephrine impact the state of smooth muscle contraction?
In the gastrointestinal tract, how would the application of norepinephrine or epinephrine impact the state of smooth muscle contraction?
What is the primary effect of an atropine blockade on acetylcholine receptors within the GI tract?
What is the primary effect of an atropine blockade on acetylcholine receptors within the GI tract?
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Which of these is NOT a common trigger of peristalsis?
Which of these is NOT a common trigger of peristalsis?
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What is the immediate consequence of a peristaltic trigger in the GI tract?
What is the immediate consequence of a peristaltic trigger in the GI tract?
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Which of the following correctly describes segmentation in the context of smooth muscle contractions?
Which of the following correctly describes segmentation in the context of smooth muscle contractions?
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How do digestive hormones like VIP, cholecystokinin, gastrin, and secretin generally affect blood vessels in the GI tract?
How do digestive hormones like VIP, cholecystokinin, gastrin, and secretin generally affect blood vessels in the GI tract?
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Which of the following accurately describes the effect of cholecystokinin (CCK) on gastrin?
Which of the following accurately describes the effect of cholecystokinin (CCK) on gastrin?
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What primary function do peristaltic waves serve in the small intestine beyond propelling chyme?
What primary function do peristaltic waves serve in the small intestine beyond propelling chyme?
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Which reflex results in increased peristaltic activity in the small intestine after a meal, and what primarily causes it?
Which reflex results in increased peristaltic activity in the small intestine after a meal, and what primarily causes it?
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What is the primary purpose of the ileocecal valve in digestive function?
What is the primary purpose of the ileocecal valve in digestive function?
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What is the primary purpose of haustrations in the colon?
What is the primary purpose of haustrations in the colon?
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What are the primary stimuli for triggering the defecation reflex?
What are the primary stimuli for triggering the defecation reflex?
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What is the primary etiology of peptic ulcers?
What is the primary etiology of peptic ulcers?
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Which of the following best describes the term 'sprue'?
Which of the following best describes the term 'sprue'?
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What is the initial physiological event in the vomiting process?
What is the initial physiological event in the vomiting process?
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Which of the following factors does NOT usually cause nausea?
Which of the following factors does NOT usually cause nausea?
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Which of the following is the primary cause of vasodilation in the GI tract due to a drop in partial pressure of oxygen?
Which of the following is the primary cause of vasodilation in the GI tract due to a drop in partial pressure of oxygen?
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What is the primary function of the heavy, alkaline mucus secretions in the cardiac region of the stomach?
What is the primary function of the heavy, alkaline mucus secretions in the cardiac region of the stomach?
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What is the main effect of the enterogastric reflex on gastric emptying?
What is the main effect of the enterogastric reflex on gastric emptying?
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In an individual experiencing achalasia, what is the primary physiological issue?
In an individual experiencing achalasia, what is the primary physiological issue?
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Which of the following actions is considered a voluntary aspect of swallowing?
Which of the following actions is considered a voluntary aspect of swallowing?
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What is the primary purpose of mastication in the digestive process?
What is the primary purpose of mastication in the digestive process?
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What is the main function of intrinsic factor produced by the stomach?
What is the main function of intrinsic factor produced by the stomach?
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What is the primary trigger for initiating a secondary peristaltic wave in the esophagus?
What is the primary trigger for initiating a secondary peristaltic wave in the esophagus?
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Which of the following best describes the sequence of actions in the chewing reflex?
Which of the following best describes the sequence of actions in the chewing reflex?
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Why does food move through the esophagus faster when a person is standing up rather than sitting down?
Why does food move through the esophagus faster when a person is standing up rather than sitting down?
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Which part of the digestive system contains skeletal muscle in its walls and receives innervation via alpha motor neurons?
Which part of the digestive system contains skeletal muscle in its walls and receives innervation via alpha motor neurons?
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What causes the stomach to make rumbling sounds?
What causes the stomach to make rumbling sounds?
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Where are the oxyntic and pyloric glands located?
Where are the oxyntic and pyloric glands located?
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What is the result of increased intensity of peristaltic contractions in the stomach as they approach the pylorus when the pyloric sphincter is closed?
What is the result of increased intensity of peristaltic contractions in the stomach as they approach the pylorus when the pyloric sphincter is closed?
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After the primary peristaltic wave, how much liquid chyme is typically squirted into the duodenum with each stomach contraction?
After the primary peristaltic wave, how much liquid chyme is typically squirted into the duodenum with each stomach contraction?
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Study Notes
Smooth Muscle Contraction
- Single-unit smooth muscle is important for peristalsis and segmentation.
- Multi-unit smooth muscle is important for sphincters.
- Smooth muscle can contract due to:
- Neural innervation
- Hormonal stimuli
- Stretch
- Slow wave potentials cause smooth muscle to be partially contracted.
GI Tract Smooth Muscle Control
- In the GI tract, stretch, acetylcholine, and some hormones stimulate smooth muscle contraction by producing slow wave depolarization.
- Norepinephrine and epinephrine inhibit smooth muscle contraction by hyperpolarizing slow waves.
- The autonomic nervous system alters contraction and secretion in the GI tract by modulating enteric nervous system activity.
- Sphincters are primarily contracted until being relaxed.
Peristalsis
- Peristalsis propels food through the GI tract (oral to anal).
- The enteric nervous system coordinates and regulates peristalsis.
- Two things that can disturb peristalsis:
- Destroying the myenteric plexus
- Blocking acetylcholine receptors (e.g., by atropine)
- Three things that can trigger peristalsis:
- Local distension (smooth muscle stretch)
- Local irritation
- Parasympathetic discharge
- The myenteric (peristaltic) reflex has 4 steps:
- Reflex occurs; GI tract contracts.
- Contraction backtracks towards the mouth.
- Smooth muscle on the anal side relaxes.
- Contractile ring moves forward towards the anal direction.
Mixing Movements (Segmentation)
- Mixing movements (e.g., segmentation) produce non-peristaltic rings in different segments.
- In the large intestine, small pouches are called haustra.
Digestive Hormones and Vasodilation
- Digestive hormones (e.g., VIP, CCK, gastrin, secretin) are vasodilators.
- Locally released compounds (e.g., kallidin, bradykinin) are potent vasodilators.
- A drop in oxygen in the GI tract causes vasodilation.
- Parasympathetic innervation causes vasodilation in GI blood vessels.
- Heavy exercise after a meal decreases blood flow to digestive cells, potentially causing cramps or shock.
Mastication (Chewing)
- Mastication is a loop reflex controlled by conscious initiation.
- Benefits of mastication:
- Increases surface area.
- Breaks down food structure.
- Prevents food scrapes.
- Five steps of the chewing reflex:
- Bolus touches mouth receptors.
- Masticatory muscles inhibit.
- Jaw drops.
- Masticatory muscles stretch.
- Masticatory muscles reflexively contract.
Swallowing
- Conscious swallowing involves voluntary tongue pushing.
- Involuntary swallowing is triggered by pharyngeal material.
- Six steps after swallowing receptor stimulation:
- Soft palate moves to protect nasal passages.
- Palatopharyngeal folds approximate to block large masses.
- Larynx moves up and anterior; epiglottis covers larynx.
- Upper esophageal sphincter relaxes.
- Pharyngeal muscles contract to move food to esophagus.
- Primary peristaltic waves are triggered by food distension.
Esophagus
- Mucus glands are concentrated at the gastric end of the esophagus to prevent acid reflux.
- Food reaches the stomach faster when standing than sitting.
- A secondary peristaltic wave is generated if food sticks after the primary wave.
- The pharynx and top third of esophagus are skeletal muscle innervated by alpha motor neurons.
- The lower two-thirds of the esophagus up to the external anal sphincter is smooth muscle.
- The enteric and autonomic nervous systems regulate the smooth muscle.
- The lower esophageal sphincter relaxes as each peristaltic wave approaches the stomach.
- Achalasia is poor lower esophageal sphincter relaxation, causing food accumulation.
- Two main muscles protecting against gastric reflux are the lower esophageal sphincter and intra-abdominal pressure.
Stomach
- Three parts of the stomach: cardiac region, fundus (body), antrum.
- The cardiac region has heavy alkaline mucus secretions.
- Weak gastric peristaltic waves are triggered by material entering the fundus; the waves spread to the antrum.
- Peristaltic contractions increase as they approach the pylorus.
- Chyme squirts into the duodenum sparingly, with closed pyloric sphincter.
- Hunger pains result from fundal contractions. Stomach rumbling is from gas movement.
- Important stomach secretions are mainly in the fundus and antrum from oxyntic and pyloric glands.
- The only indispensable function of the stomach is producing intrinsic factor for vitamin B12 absorption.
- Chyme becomes more fluid in the stomach and intense peristaltic waves are triggered closer to the duodenum. This is mildly stimulated by gastrin.
Duodenum and Small Intestine
- The duodenum tends to inhibit gastric emptying.
- The enterogastric reflex inhibits gastric emptying.
- Four stimuli trigger the enterogastric reflex: low pH, amino acids/peptides, hypotonic/hypertonic chyme, fat.
- CCK is released due to fat in the duodenum. CCK (and secretin) block gastrin's effects.
- Peristaltic waves mix and layer chyme in the small intestine for absorption.
- Peristaltic waves increase after a meal due to the gastroenteric reflex.
- Secretin and glucagon can inhibit the gastroenteric reflex and small intestine motility.
Large Intestine
- The myenteric plexus is the nervous supply between the inner and outer muscle layers.
- The peristaltic rush is strong long waves caused by local irritation, quickly moving chyme to the anus.
- The ileocecal valve connects the small and large intestines.
- The colon absorbs water and ions.
- Enteritis is inflammation of the intestine, causing diarrhea.
- Mixing movements in the colon are hausrations, to absorb water and ions and propel chyme.
Defecation
- The defecation reflex is triggered by feces in the rectum.
- The rectum relaxes, internal and external anal sphincters relax.
- Cortical and subcortical control regulates defecation by consciously relaxing the external anal sphincter.
Other Digestive Issues
- Peptic ulcers are caused by H. pylori bacteria.
- Sprue causes malabsorption.
- Constipation is suppression of defecation reflexes, potentially causing megacolon.
- Flatus is gas in the GI tract (swallowed or produced). Primary gases are CO2, methane, and hydrogen gas.
- Nausea is caused by the chemoreceptor trigger zone in the brainstem, triggered by blood contents.
- Vomiting has 10 steps: distension, triggering the vomiting center, antiperistalsis, chyme distension, strong contractions, sphincter relaxation, airway protection, diaphragm and abdominal muscle contractions, and chyme expulsion.
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Description
This quiz explores the mechanisms of smooth muscle contraction in the gastrointestinal tract, focusing on single-unit and multi-unit smooth muscle. Learn about the factors that influence contraction and the role of the autonomic nervous system in regulating peristalsis and sphincter functions.
