Guyton Ch. 64 Propulsion and Mixing of Food in the Alimentary Tract
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Questions and Answers

What controls the timing of mixing and propulsion activities in the alimentary tract?

  • Appetite
  • Intrinsic desire for food
  • Hormonal mechanisms
  • Automatic nervous mechanisms (correct)

    • Which chapter discusses the mechanisms of food ingestion, especially mastication and swallowing?

  • Chapter 48
  • Chapter 64 and Chapter 72
  • Chapter 64 (correct)
  • Chapter 72

    • What type of teeth provide a strong cutting action for chewing?

  • Molars
  • Canines
  • Incisors (correct)
  • Premolars

    • What determines the amount of food that a person ingests?

    <p>Hunger</p> Signup and view all the answers

    Which teeth provide a grinding action for chewing?

    <p>Molars</p> Signup and view all the answers

    What is discussed in Chapter 72 in relation to the body's nutrition?

    <p>Mechanisms for maintaining an adequate nutritional supply</p> Signup and view all the answers

    What is the primary function of the intense peristaltic contractions in the stomach during stomach emptying?

    <p>Forcing up to several milliliters of chyme into the duodenum</p> Signup and view all the answers

    What is the role of the pyloric sphincter in stomach emptying?

    <p>To prevent passage of food particles until they become almost fluid consistency</p> Signup and view all the answers

    Which factor promotes increased emptying from the stomach?

    <p>Stretching of the stomach wall</p> Signup and view all the answers

    Which factor can initiate enterogastric inhibitory reflexes from the duodenum?

    <p>Presence of breakdown products of fats in the chyme</p> Signup and view all the answers

    What is the effect of the hormone gastrin on stomach emptying?

    <p>Promotes stomach emptying</p> Signup and view all the answers

    What happens if the pH of the chyme in the duodenum falls below about 3.5 to 4?

    <p>Stops further release of acidic stomach contents into the duodenum</p> Signup and view all the answers

    What is the primary effect of enterogastric inhibitory reflexes?

    <p>Inhibit stomach emptying</p> Signup and view all the answers

    What are the types of factors that are continually monitored in the duodenum to initiate enterogastric inhibitory reflexes?

    <p>Distention of the duodenum, presence of irritation of the duodenal mucosa, and acidity of the chyme</p> Signup and view all the answers

    What is the role of the intense peristaltic contractions in causing stomach emptying?

    <p>Gradually pinching off food in the body of the stomach</p> Signup and view all the answers

    What effect does increased food volume in the stomach have on stomach emptying?

    <p>It elicits local myenteric reflexes that accentuate activity</p> Signup and view all the answers

    What is a significant effect of stretching of the stomach wall on stomach emptying?

    <p>It accentuates activity of the pyloric pump</p> Signup and view all the answers

    Which factor elicits inhibitory enterogastric reflexes to slow or stop stomach emptying?

    <p>Breakdown products of fats</p> Signup and view all the answers

    Which cranial nerve innervates most of the muscles of chewing?

    <p>Fifth cranial nerve</p> Signup and view all the answers

    What force can all the jaw muscles working together close the molars with?

    <p>200 pounds</p> Signup and view all the answers

    What initiates reflex inhibition of the muscles of mastication during chewing?

    <p>Presence of a bolus of food in the mouth</p> Signup and view all the answers

    Why is chewing especially important for most fruits and raw vegetables?

    <p>They have indigestible cellulose membranes around their nutrient portions</p> Signup and view all the answers

    What is the principal reason that grinding the food to a very fine particulate consistency aids digestion?

    <p>Increases surface area exposed to digestive secretions</p> Signup and view all the answers

    What initiates a series of automatic pharyngeal muscle contractions during the involuntary pharyngeal stage of swallowing?

    <p>Bolus of food entering the posterior mouth and pharynx</p> Signup and view all the answers

    What is the main role of the pharynx during swallowing?

    <p>Subserves respiration and swallowing</p> Signup and view all the answers

    What prevents reflux of food into the nasal cavities during the involuntary pharyngeal stage of swallowing?

    <p>Soft palate is pulled upward to close the posterior nares</p> Signup and view all the answers

    What is the function of the valvelike mechanism of the lower esophagus?

    <p>To prevent high intra-abdominal pressure from pushing stomach contents into the esophagus</p> Signup and view all the answers

    What is the role of vagovagal reflex in the stomach?

    <p>To reduce the tone in the muscular wall of the stomach</p> Signup and view all the answers

    What initiates the mixing waves in the stomach?

    <p>Basic electrical rhythm of the stomach wall</p> Signup and view all the answers

    What is the main role of the peristaltic constrictor rings in the antrum of the stomach?

    <p>To squeeze antral contents upstream through retropulsion</p> Signup and view all the answers

    What determines the degree of fluidity of chyme leaving the stomach?

    <p>The degree of digestion that has occurred</p> Signup and view all the answers

    What causes hunger pangs in individuals after prolonged fasting?

    <p>Decreased levels of blood sugar</p> Signup and view all the answers

    What happens when hunger contractions become extremely strong in the body of the stomach?

    <p>They fuse to cause a continuing tetanic contraction</p> Signup and view all the answers

    How are hunger contractions affected by gastrointestinal tonus?

    <p>They are most intense in individuals with high gastrointestinal tonus</p> Signup and view all the answers

    What promotes stomach emptying?

    <p>Intense peristaltic contractions in the antrum</p> Signup and view all the answers

    What is the main role of cholecystokinin (CCK) in inhibiting gastric emptying?

    <p>Inhibiting the pyloric pump and increasing the strength of contraction of the pyloric sphincter</p> Signup and view all the answers

    What stimulates the release of inhibitory hormones from the upper intestine?

    <p>Fats entering the duodenum</p> Signup and view all the answers

    Which hormone has a general but weak effect of decreasing gastrointestinal motility?

    <p>Gastric inhibitory peptide (GIP)</p> Signup and view all the answers

    What are the two main conditions under which the rate of stomach emptying is slowed by inhibitory feedback signals from the duodenum?

    <p>Too much chyme in the small intestine and excessively acidic chyme</p> Signup and view all the answers

    What is the main effect of gastric inhibitory peptide (GIP) at physiological concentrations?

    <p>Stimulates secretion of insulin by the pancreas</p> Signup and view all the answers

    What is the main role of secretin in relation to stomach emptying?

    <p>Inhibiting gastric emptying</p> Signup and view all the answers

    What is one of the factors that can limit the rate of stomach emptying?

    <p>Inhibitory feedback signals from the duodenum</p> Signup and view all the answers

    What is the primary function of the esophagus?

    <p>To conduct food rapidly from the pharynx to the stomach</p> Signup and view all the answers

    Where are the most sensitive tactile areas for initiating the pharyngeal stage of swallowing located?

    <p>Around the pharyngeal opening, with greatest sensitivity on the tonsillar pillars</p> Signup and view all the answers

    Which nerves transmit impulses from the sensitive areas of the mouth and pharynx to the medulla oblongata?

    <p>Trigeminal and glossopharyngeal nerves</p> Signup and view all the answers

    What controls the orderly sequence of swallowing reflex?

    <p>Reticular substance of the medulla and lower portion of the pons</p> Signup and view all the answers

    What term is used to collectively describe the areas in the medulla and lower pons that control swallowing?

    <p>Deglutition center</p> Signup and view all the answers

    Which type of peristalsis results from distention of the esophagus by retained food?

    <p>Secondary peristalsis</p> Signup and view all the answers

    What causes initiation of secondary peristaltic waves in the esophagus?

    <p>Reflexes initiated by vagal afferent fibers to the esophagus</p> Signup and view all the answers

    Which nerves control peristaltic waves in the upper third of the esophagus?

    <p>Glossopharyngeal and vagus nerves</p> Signup and view all the answers

    What happens when vagus nerves to the esophagus are cut?

    <p>The myenteric nerve plexus becomes excitable enough to cause strong secondary peristaltic waves without support from vagal reflexes</p> Signup and view all the answers

    What is receptive relaxation of the stomach?

    <p>'Digestive relaxation' that prepares the stomach for receiving food from the esophagus</p> Signup and view all the answers

    What is another name for the lower esophageal sphincter?

    <p>'Cardiac sphincter'</p> Signup and view all the answers

    What is the main role of segmentation contractions in the small intestine?

    <p>To divide the intestine into spaced segments</p> Signup and view all the answers

    What determines the maximum frequency of segmentation contractions in the small intestine?

    <p>Frequency of electrical slow waves in the intestinal wall</p> Signup and view all the answers

    Under what conditions does the maximum frequency of the segmentation contractions occur?

    <p>When extreme stimulation is exerted on the intestinal wall</p> Signup and view all the answers

    What is the role of electrical slow waves in the intestinal wall?

    <p>To determine the frequency of segmentation contractions</p> Signup and view all the answers

    What effect does stretching of the intestinal wall have on segmentation contractions?

    <p>Initiates a new set of segmentation contractions</p> Signup and view all the answers

    How do segmentation contractions contribute to food mixing with secretions in the small intestine?

    <p>By dividing the intestine into spaced segments</p> Signup and view all the answers

    What is the velocity of peristaltic waves as they move toward the anus in the small intestine?

    <p>0.5 to 2.0 cm/sec</p> Signup and view all the answers

    What is the main cause of the increased peristaltic activity in the small intestine after a meal?

    <p>Beginning entry of chyme into the duodenum</p> Signup and view all the answers

    What is the role of serotonin in relation to small intestinal motility?

    <p>Enhances intestinal motility</p> Signup and view all the answers

    What is the primary function of the peristaltic waves in the small intestine?

    <p>Cause progression of chyme toward the ileocecal valve and spread out the chyme along the intestinal mucosa</p> Signup and view all the answers

    What initiates intense peristaltic contractions called 'peristaltic rush' in the small intestine?

    <p>Intense irritation of the intestinal mucosa</p> Signup and view all the answers

    What is the role of muscularis mucosae in the small intestine?

    <p>Cause short folds to appear in the intestinal mucosa and increase absorption</p> Signup and view all the answers

    What is the function of the ileocecal valve?

    <p>Prevent backflow from the colon to the small intestine</p> Signup and view all the answers

    What is the resistance capability of the ileocecal valve against reverse pressure?

    <p>&gt;50 to 60 centimeters of water</p> Signup and view all the answers

    What causes resistance to emptying at the ileocecal valve?

    <p>Ileocecal sphincter constriction</p> Signup and view all the answers

    What is the typical rate of travel for net movement along the small intestine?

    <p>~1 cm/min</p> Signup and view all the answers

    'Peristaltic rush' is initiated partly by intrinsic enhancement of which reflexes?

    <p>(Myenteric plexus) reflexes in the gut wall</p> Signup and view all the answers

    What is a significant effect of stretching of the stomach wall on stomach emptying?

    <p>Delay stomach emptying</p> Signup and view all the answers

    What prevents continual dribble of fecal matter through the anus?

    <p>Conscious signals inhibiting the external sphincter constriction</p> Signup and view all the answers

    What converts the intrinsic myenteric defecation reflex into a powerful process of defecation?

    <p>Parasympathetic defecation reflex involving the sacral segments of the spinal cord</p> Signup and view all the answers

    What causes automatic emptying of the lower bowel in newborns and some people with transected spinal cords?

    <p>Lack of conscious control exercised through voluntary contraction or relaxation of the external anal sphincter</p> Signup and view all the answers

    What is the role of the peritoneointestinal reflex?

    <p>Strongly inhibits excitatory enteric nerves, causing intestinal paralysis</p> Signup and view all the answers

    Which reflex inhibits intestinal activity as a result of kidney irritation?

    <p>Renointestinal reflex</p> Signup and view all the answers

    What initiates enterogastric inhibitory reflexes to slow or stop stomach emptying?

    <p>Stretching of the stomach wall</p> Signup and view all the answers

    What is one of the functions of vagovagal reflex in the stomach?

    <p>Inhibition of excitatory enteric nerves</p> Signup and view all the answers

    What is one effect of increased food volume in the stomach on stomach emptying?

    <p>Slowing down of stomach emptying</p> Signup and view all the answers

    What is the role of the cecum in controlling the ileocecal sphincter and ileal peristalsis?

    <p>Intensifying contraction of the ileocecal sphincter</p> Signup and view all the answers

    Which factor promotes increased emptying from the stomach?

    <p>Stimulation of intense peristaltic contractions</p> Signup and view all the answers

    How are reflexes from the cecum to the ileocecal sphincter and ileum mediated?

    <p>By both the myenteric plexus and extrinsic autonomic nerves</p> Signup and view all the answers

    What happens when vagus nerves to the esophagus are cut?

    <p>Loss of involuntary control over swallowing</p> Signup and view all the answers

    What characterizes the movements of the colon during absorption and storage functions?

    <p>Slow and sluggish movements</p> Signup and view all the answers

    What is the main effect of gastric inhibitory peptide (GIP) at physiological concentrations?

    <p>Slowing down stomach emptying</p> Signup and view all the answers

    What can be observed during mixing movements in the large intestine?

    <p>Baglike sacs called haustrations due to combined circular and longitudinal muscle contractions</p> Signup and view all the answers

    What is one function of peristaltic constrictor rings in the antrum of the stomach?

    <p>Initiation of intense peristaltic contractions in the stomach</p> Signup and view all the answers

    What is a characteristic of propulsive movements in the colon?

    <p>A series of mass movements persisting for 60-90 minutes</p> Signup and view all the answers

    What initiates mass movements in the colon after meals?

    <p>Distention of the stomach and duodenum</p> Signup and view all the answers

    What contributes to maintaining an empty rectum most of the time?

    <ul> <li>Presence of a weak functional sphincter near the sigmoid colon-rectum juncture</li> </ul> Signup and view all the answers

    What effect does a mass movement have in causing the desire for defecation?

    <ul> <li>Forcing feces into the rectum</li> </ul> Signup and view all the answers

    What stimulates mass movements after meals?

    <p>Constriction at points distended or irritated in the colon</p> Signup and view all the answers

    What contributes to progressive absorption of fluid and dissolved substances in the large intestine?

    <p>Haustral contractions rolling over fecal material</p> Signup and view all the answers

    What is a key characteristic of propulsive movements known as mass movements?

    <p>Contraction force developing progressively for about 30 seconds</p> Signup and view all the answers

    What leads to defecation when a mass movement forces feces into the rectum?

    <p>Relaxation of anal sphincters in response to rectal distention</p> Signup and view all the answers

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