63 Questions
What is the function of the sphincter of Oddi in the GI tract?
Delivers stored bile to the intestine
How long does it take for significant absorption of nutrients to occur in the GI tract, based on the information provided?
7-10 hours
Which part of the GI tract mixes and grinds food while it stays in it for 1-4 hours?
Stomach
What is the purpose of mastication of food in the digestive process?
Creates bolus that can be swallowed
Which organ is essential for secreting digestive enzymes in the GI tract?
Pancreas
What is the main purpose of the large intestine in the digestive process?
Transports fluids and electrolytes
What is the main function of internal and external anal sphincters?
Maintain positive resting pressure
Which stimuli induce sphincteric contraction?
Distal stimuli
What innervates most muscles of mastication?
Motor branch of CN V
What is the purpose of chewing in digestion?
Act on food particle surface only
What happens when a bolus of food is in the mouth?
Jaw drops
During swallowing, what prevents food from entering the trachea?
Epiglottis covering the glottis
What initiates mixing waves in the stomach after food ingestion?
Antral peristaltic contractions
What is the function of the pyloric pump in the stomach?
To force chyme into the duodenum
When do hunger contractions typically begin post-prandially?
12-24 hours after eating
What triggers the receptive relaxation of the stomach?
Movement of pharynx and esophagus
Which factor most prominently enhances the activity of the pyloric pump?
Gastrin secretion
What is one factor that inhibits gastric emptying according to the text?
Inhibitory signals from the duodenum
Which of the following can inhibit gastric emptying?
Excessive acidity in the chyme
What is the role of CCK in the hormonal feedback related to gastric emptying?
Inhibiting gastric emptying
What is the main function of Ileocecal valve?
To resist reflux from the cecum
Which signals greatly increase peristalsis in the small intestine after meals?
Nervous signals
What types of movements help to propel chyme in the small intestine?
Segmentation and peristalsis
How does the mucosal muscle contribute to the movement of lymph in the small intestine?
By extending into intestinal villi to facilitate lymph flow
Which sphincter is most critical for preventing aspiration of stomach contents?
Lower esophageal sphincter
What process involves signaling between the pharynx and the swallowing center in the brain stem?
Deglutition
Which structure is responsible for determining if a food bolus is small enough to be swallowed?
Epiglottis
What increases barrier pressure to reduce the likelihood of aspiration during medical procedures?
Administering cricoid pressure during induction
Which movement involves signaling between the pharynx and the brain stem?
Pharyngeal peristalsis
What is the main function of the sphincter of Oddi in the GI tract?
Regulate bile and pancreatic juice entry into the duodenum
Which structure is responsible for determining if a food bolus is small enough to be swallowed?
Pharynx
What triggers the receptive relaxation of the stomach?
Swallowing
During swallowing, what prevents food from entering the trachea?
Larynx movement
What increases barrier pressure to reduce the likelihood of aspiration during medical procedures?
Glottis closure
What is one factor that inhibits gastric emptying according to the provided content?
High barrier pressure
What role do internal and external anal sphincters play in the digestive system?
Maintain positive resting pressure to prevent involuntary defecation
What stimulates mass movements in the colon after a meal?
Distention of the stomach
What prevents fecal matter from dribbling through the anus?
Tonic constriction of the internal anal sphincter
Which stimuli induce sphincteric contraction in the digestive system?
Distal stimuli
What is the primary purpose of mastication in the digestive process?
To aid in the digestion of cellulose membranes
Why are newborns and individuals with transected spinal cords unable to control their external anal sphincter?
Weak intrinsic myenteric reflex
What is the primary function of large circular contractions in the colon?
Mixing of chyme
How many times is a typical food bolus chewed before passing through the esophagus without pain?
25-30 times
Which reflex is essential for fortifying the parasympathetic defecation reflex?
Duodenocolic reflex
What triggers the stretch reflex leading to rebound contraction during chewing?
Jaw dropping when a bolus of food is in the mouth
Which muscle group is primarily responsible for mastication and is innervated by a motor branch of CN V?
Muscles of mastication
What is the main function of teniae coli in the colon?
Propulsion of feces into the rectum
What is the role of migrating motor complexes (MMCs) in the small intestine?
Interrupt at 90-minute intervals to move indigestible components
What is the main function of the ileocecal valve?
Prevent backflow from the colon to the small intestine
How does the mucosal muscle contribute to intestinal function?
Increase barrier pressure to reduce aspiration risk
Which signals greatly increase peristalsis in the small intestine after meals?
Gastrin, CCK, insulin, motilin
What factor primarily affects gastric emptying based on the information provided?
Tonicity of the chyme
Which type of movements help propel chyme in the small intestine?
Peristaltic movements
What is the primary action of the soft palate during the pharyngeal stage of deglutition?
Prevent food reflux
How does the cricopharyngeus muscle behave during the pharyngeal stage of deglutition?
Relaxes to allow food passage
What is the main function of the upper esophageal sphincter (UES) during deglutition?
Prevents gastric reflux
Which structure plays a significant role in preventing regurgitation and aspiration of gastric contents?
LES pressure
How is the barrier pressure calculated in the context of gastroesophageal reflux prevention?
LES pressure - Intragastric pressure
What effect does pregnancy have on the lower esophageal sphincter (LES)?
Decreases LES tone
Which condition is characterized by the failure of smooth muscle motility and relaxation of the lower esophageal sphincter (LES)?
Achalasia
'Barrett's esophagitis' is associated with which transformation in the lower esophagus?
'GI metaplasia'
'Carcinoma of upper esophagus' is most commonly related to which lifestyle factor?
'Smoking/alcohol use'
'Gastroesophageal Reflux Disease (GERD)' can lead to which critical issue for patients with heartburn?
'Lower barrier pressure'
Study Notes
Propulsion and Mixing of Food in the Alimentary Tract
Ingestion of Food
- Ingestion of food involves the breakdown of food into smaller particles and mixing with digestive enzymes and acids
- Mastication (chewing) is important for breaking down cellulose membranes, allowing digestive enzymes to act on food particles
Three Main Functions of GI Tract
- Churning: enhances digestion and absorption of nutrients
- Propulsion: caudal movement of food/waste
- Acts as a reservoir: facilitated by sphincters
Sphincters
- Specialized circular muscles that act as one-way valves
- Regulate antegrade and retrograde movement
- Proximal stimuli cause sphincteric relaxation, distal stimuli induce sphincteric contraction
- Separate low-pressure organs, maintain positive resting pressure, and coordinate with adjacent organs by intrinsic and neurohumoral stimuli
Mastication
- Most muscles of mastication are innervated by the motor branch of CN V
- Chewing is important for breaking down cellulose membranes
- A bolus of food in the mouth causes the jaw to drop, followed by a stretch reflex and rebound contraction
Deglutition
- Three stages: voluntary, pharyngeal, and esophageal
- Pharyngeal stage: involuntary, stimulated by sensitive epithelial swallowing receptor areas, and controlled by CNs IX, X, and XII
- Esophageal stage: involuntary, assisted by gravity, and controlled by primary and secondary peristalsis
Structures of the Esophagus
- Upper esophageal sphincter (UES): skeletal muscle, controlled by extrinsic cranial nerves
- Esophageal body: skeletal and smooth muscle, remains relaxed
- Lower esophageal sphincter (LES): circular smooth muscle, controlled by ENS, and tonically constricted
Motor Functions of the Stomach
- During fasting, the stomach is quiescent
- With ingestion of food, the stomach undergoes receptive relaxation, mixing waves, and gastric emptying
- Gastric emptying is regulated by signals from the duodenum and stomach
Regulation of Stomach Emptying
- Factors promoting emptying: stretching of the stomach wall, gastrin, and activity of the pyloric pump
- Factors inhibiting emptying: inhibitory signals from the duodenum, including CCK and hormonal feedback
Movements of the Small Intestine
- Segmentation movements: "chop" the chyme
- Peristalsis: propels chyme, increased after meals
- Migrating motor complexes (MMCs): interrupt at 90-minute intervals to move indigestible components
Ileocecal Valve
- Prevents backflow from the colon to the small intestine
- Forcefully closed when excess pressure builds in the cecum
- Resists reflux, and normally 1500-2000 ml of chyme empty into the cecum each day
Principle Functions of the Colon
- Absorption of water and electrolytes from chyme to form solid feces
- Storage of fecal matter until expelled
- Mixing movements: haustrations, and large circular contractions
Defecation
- Rectum is usually empty of feces
- Dribble of fecal matter through the anus is prevented by tonic constriction of the internal and external anal sphincters
- Defecation is stimulated by the gastrocolic and duodenocolic reflexes, and occurs 1-3 times a day
Test your knowledge on the sequence of events in the digestive system, from mouth to stomach to small intestine. Identify the process of mastication, secretion of gastric acid, and food movement through different organs.
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