GI Reflexes Overview L8
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Questions and Answers

What is the primary function of the entero-gastric reflex?

  • To enhance digestion in the colon
  • To stimulate stomach secretion
  • To inhibit stomach motility and secretion (correct)
  • To promote peristalsis in the small intestine

    • Which reflex is primarily responsible for the evacuation of the colon in response to signals from the stomach?

  • Gastrocolic reflex (correct)
  • Defecation reflex
  • Colonoileal reflex
  • Enterogastric reflex

    • Which type of GI reflex is responsible for long-distance signaling between different areas of the GI tract?

  • Reflexes that involve the spinal cord or brainstem
  • Reflexes integrated within the gut wall
  • Local inhibitory reflexes
  • Reflexes involving prevertebral sympathetic ganglia (correct)

    • Pain reflexes within the GI system typically result in what type of reaction?

    <p>General inhibition of GI tract activity</p> Signup and view all the answers

    Which reflex is associated with the contractions necessary for defecation?

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

    What are examples of a type one GI reflex?

    <p>Those that control GI secretion, such as peristalsis, mixing contractions, and local inhibitory effects</p> Signup and view all the answers

    What are the three types of Type 2 GI reflexes?

    <p>They are the gastrocolic reflex, enters gastric reflex and colonoileal reflex</p> Signup and view all the answers

    The pain and defecation reflex are which type of GI reflex?

    <p>Type 3</p> Signup and view all the answers

    Which of the following best describes the pathway of the defecation reflex?

    <p>Signals move from the colon and rectum to the spinal cord and back, triggering colonic, rectal, and abdominal contractions for defecation</p> Signup and view all the answers

    What initiates the peristaltic reflex in the intestinal wall?

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

    What is primarily responsible for the smooth muscle contraction proximal to the site of distention during peristalsis?

    <p>Acetylcholine and substance P</p> Signup and view all the answers

    How do the longitudinal and circular musculature work together during peristalsis?

    <p>They perform opposite actions in coordination</p> Signup and view all the answers

    What role do afferent neurons play in the peristaltic reflex?

    <p>They relay the sensation of stretching and initiate reflexive actions</p> Signup and view all the answers

    What is the function of the inhibitory motor neurons distal to the site of distention in the peristaltic reflex?

    <p>They promote relaxation of the circular muscle</p> Signup and view all the answers

    What type of neurons in the peristaltic reflex are stimulated proximal to the site of extension?

    <p>Excitatory motor neurons are stimulated.</p> Signup and view all the answers

    Distal to the site of distention (in peristaltic reflex), (inhibitory/excitatory) motor neurons are stimulated to release NO, ATP or VIP for smooth muscle relaxation of circular muscle?

    <p>Inhibitory motor neurons are stimulated distal to the site of distension</p> Signup and view all the answers

    Which of the following best describes the vagovagal reflex ?

    <p>Coordinates contraction of GI muscles in response to chyme digestion</p> Signup and view all the answers

    What role do the afferent fibers of the vagus nerve play in the vagovagal reflex?

    <p>They transmit sensory signals from the gastric mucosa.</p> Signup and view all the answers

    During which process is the vagovagal reflex particularly active?

    <p>The active relaxation of the stomach during digestion.</p> Signup and view all the answers

    What stimulates the vagal afferent fibers to activate the vagovagal reflex?

    <p>Mechanical receptors in the gastric mucosa.</p> Signup and view all the answers

    Which part of the central nervous system is involved in coordinating the vagovagal reflex?

    <p>The dorsal vagal complex.</p> Signup and view all the answers

    Which of the following best represents the path of the vagovagal reflex?

    <p>From the stomach to the brain and back to the stomach.</p> Signup and view all the answers

    What primary function does the distal region of the stomach serve?

    <p>Grinding and sieving of food particles</p> Signup and view all the answers

    What is the main role of the proximal region of the stomach?

    <p>Storing food until it moves to the small intestine</p> Signup and view all the answers

    Which characteristic distinguishes the grinding function of the stomach?

    <p>It reduces food into particles small enough for digestion</p> Signup and view all the answers

    Which statement about the stomach's anatomical regions is correct?

    <p>The corpus has distinct functions between its proximal and distal parts.</p> Signup and view all the answers

    The main purpose of the “gastric pump” in the stomach’s distal region is to:

    <p>Grind food into smaller particles for digestion.</p> Signup and view all the answers

    What initiates the influx of contents into the gastric pump?

    <p>Tonic contraction of the fundus</p> Signup and view all the answers

    Which cellular structures are responsible for causing slow waves in the stomach's smooth muscle cells?

    <p>Interstitial cells of Cajal</p> Signup and view all the answers

    Which statement correctly describes the relationship between spike potentials and smooth muscle contraction in the stomach?

    <p>Contraction of smooth muscle cells occurs when spike potentials occur</p> Signup and view all the answers

    What is the sequence of events that occurs after strong peristaltic waves in the corpus of the stomach?

    <p>Transport to the pylorus followed by emptying into the duodenum</p> Signup and view all the answers

    Which of the following describes the primary mechanism by which fluids and solid particles are emptied from the stomach into the duodenum?

    <p>Fluid moves in faster due to lower viscosity</p> Signup and view all the answers

    The grinding action occurs in the proximal region

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

    What are the three things that can trigger the vagus center to relax the stomach?

    <p>It is the receptive relaxation, adaptive relaxation and feed-back relaxation</p> Signup and view all the answers

    What occurs primarily during the digestive period of intestinal motility?

    <p>Fast aboral migrating contractions</p> Signup and view all the answers

    Which of the following accurately describes segmentation contractions in the small intestine?

    <p>They enhance nutrient absorption by mixing food with digestive juices.</p> Signup and view all the answers

    What is the primary function of peristalsis in the small intestine?

    <p>To propel chyme in the aboral direction</p> Signup and view all the answers

    Which statement best describes the differences in the motility of the small intestine's regions?

    <p>The duodenum has faster contraction patterns than the jejunum.</p> Signup and view all the answers

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

    <p>To enhance the mechanical breakdown of food by evenly mixing it with digestive juices</p> Signup and view all the answers

    During which phase is the migrating motor complex (MMC) primarily active?

    <p>During the interdigestive period when the intestine is empty between meals</p> Signup and view all the answers

    In which segment of the small intestine are peristaltic waves the fastest?

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

    What is the primary contribution of the non-propulsive pattern in intestinal motility?

    <p>To help in the absorption of nutrients when concentration is high</p> Signup and view all the answers

    What is the function of the MIgrating Motoric Complex (MMC)?

    <p>It helps pushing undigested material out of the intestine and controls bacterial population</p> Signup and view all the answers

    How many phases does the Migrating Motoric Complex consist of?

    <p>3</p> Signup and view all the answers

    What occurs during Phase 2 of the migrating motor complex?

    <p>Intermittent and irregular contractions, with some stronger than others.</p> Signup and view all the answers

    Which statement best describes the function of Phase 3 in the migrating motor complex?

    <p>It triggers strong peristaltic contractions starting from the stomach.</p> Signup and view all the answers

    Which of the following phases of the migrating motor complex demonstrates no contractions?

    <p>Phase 1</p> Signup and view all the answers

    How does Phase 2 of the migrating motor complex differ from Phase 3?

    <p>Phase 2 has irregular contractions, while Phase 3 has strong peristaltic contractions.</p> Signup and view all the answers

    Which phase serves primarily as a preparatory phase before intense digestive action occurs in the migrating motor complex?

    <p>Phase 1</p> Signup and view all the answers

    Which type of contraction is primarily responsible for diarrhea due to an increase in frequency or volume of defecation?

    <p>Secretory contractions</p> Signup and view all the answers

    What physiological mechanism is involved during vomiting that leads to the relaxation of the lower esophageal sphincter?

    <p>Contraction of abdominal musculature</p> Signup and view all the answers

    Which condition is associated with inadequate absorption of secreted water due to destruction of villi?

    <p>Malabsorptive diarrhea</p> Signup and view all the answers

    What is the primary function of oral migrating contractions in the context of gastrointestinal motility?

    <p>Impeding the movement of ingesta</p> Signup and view all the answers

    Which statement correctly describes the sequence of events that lead to vomiting?

    <p>Increase in abdominal pressure followed by relaxation of the upper esophageal sphincter</p> Signup and view all the answers

    Which of the following would NOT typically induce vomiting?

    <p>Flatulence caused by gastrointestinal gas</p> Signup and view all the answers

    What structural component primarily ensures continence during the defecation reflex?

    <p>Internal and external sphincters</p> Signup and view all the answers

    In the context of gastrointestinal motility, what is the primary cause of secretory diarrhea?

    <p>Increased intestinal secretion due to enterotoxins</p> Signup and view all the answers

    Study Notes

    GI Reflexes

    • Three main types of GI reflexes control gastrointestinal function.
    • Intrinsic reflexes: These are integrated within the gut wall and control local functions such as secretion, peristalsis, mixing contractions, and inhibition.
    • Extrinsic reflexes: These involve the prevertebral sympathetic ganglia and transmit signals long distances within the GI tract. Examples include:
      • Gastrocolic reflex: Signals from the stomach trigger colonic evacuation.
      • Enterogastric reflex: Signals from the colon and small intestine inhibit stomach motility and secretion.
      • Colonoileal reflex: Signals from the colon inhibit ileal emptying into the colon.
    • Central reflexes: These involve the spinal cord or brainstem and regulate GI activity.
      • Reflexes from the stomach and duodenum to the brainstem control gastric motor and secretory activity.
      • Pain reflexes can cause general inhibition of the entire GI tract.
      • The defecation reflex originates in the colon and rectum, travels to the spinal cord, and returns to stimulate contractions for defecation.

    Peristaltic Reflex Overview

    • The passage of a bolus through the intestinal wall triggers a reflex that constricts the lumen behind the bolus and dilates the lumen ahead.
    • This coordinated movement of the longitudinal and circular musculature propels the chyme along the digestive tract.
    • Peristalsis is a characteristic of many syncytial smooth muscle cells.
    • Stimulation of a point in the gut can cause a contractile ring to form in the circular muscle, which then spreads along the gut tube.
    • This phenomenon also occurs in other tissues like the bile duct and ureters.

    Peristalsis Mechanism

    • Stretching of the intestinal wall stimulates afferent sensory neurons. These mechanosensitive neurons communicate with interneurons, triggering two effects:

      • Proximal to the site of distention: Excitatory motor neurons are stimulated, releasing acetylcholine (Ach) and substance P (SP). This leads to smooth muscle contraction, specifically in the circular muscle layer.
      • Distal to the site of distention: Inhibitory motor neurons are stimulated, releasing nitric oxide (NO), adenosine triphosphate (ATP), and vasoactive intestinal peptide (VIP). This results in smooth muscle relaxation, particularly in the circular muscle layer.

    • The direction of chyme propulsion is from the oral (mouth) end towards the aboral (anus) end.

    • For the coordinated movement, circular and longitudinal musculature exhibit opposite actions: one contracts while the other relaxes.

    Vago-vagal Reflex

    • The vagovagal reflex is a gastrointestinal reflex circuit.
    • The reflex is coordinated by afferent and efferent fibers of the vagus nerve.
    • The dorsal vagal complex in the brain is involved in the reflex.
    • Stimulation of mechanical receptors in the gastric mucosa stimulates the vagus afferent fibers.
    • The vagovagal reflex is active during receptive relaxation of the stomach in response to food mastication and deglutition.
    • Once food is in the stomach, the vagovagal reflex causes active relaxation of smooth muscle in the stomach wall.
    • The reflex involves the stomach, brain, and then back to the stomach.

    Functional and Motor Subdivision of the Stomach

    • The stomach can be divided into two main regions: the distal region and the proximal region.
    • The distal region, also known as the antrum or lower part of the corpus, is responsible for grinding and sieving food.
    • This function is often referred to as the "gastric pump."
    • The distal region breaks down solid food particles into smaller pieces suitable for digestion in the small intestine.
    • The proximal region, also known as the fundus or upper part of the corpus, acts as a storage compartment for food.
    • It retains food until it is ready to be passed into the small intestine.

    Gastric Pump Dynamics

    • Inflow into the "gastric pump" is orchestrated by a series of sequential events:

      • Tonic contraction of the fundus (gastric store)
      • Strong peristaltic wave in the corpus
      • Passage into the grinder and then into the pylorus
      • Emptying of fluid and pre-digested particles into the duodenum, with fluids emptying faster than solid particles.

    • Interstitial cells of Cajal (ICC) act as pacemakers, generating slow waves in smooth muscle cells.

    • Contraction of smooth muscle cells occurs when spike potentials occur. This is crucial for the peristaltic wave and the movement of food through the stomach.

    Intestinal Motility Functions

    • Mixing and Contact: Intestinal motility mixes food with digestive juices and enhances contact between the intestinal wall and food.
    • Propulsion: Peristalsis propels chyme (partially digested food) distally (toward the anus).

    Small Intestine Motility Phases

    • Digestive Period:
      • Propulsive pattern: peristaltic waves move chyme distally.
      • Peristaltic wave speed varies: fastest in the duodenum, medium in the jejunum, and slowest in the ileum.
    • Interdigestive Period:
      • Non-propulsive pattern: segmentation contractions occur.
      • Segmentation contractions: localized contractions of circular muscle, dividing the gut into constricted and dilated segments.
      • Segmentation contractions are important for nutrient absorption when concentration is high, but do not contribute significantly to propulsion.

    Intestinal Motility Functions

    • Facilitates mixing of food with digestive juices
    • Enhances contact between food and the intestinal wall
    • Propels chyme (partially digested food) towards the anus through peristalsis

    Small Intestine Motility Phases

    • Digestive Phase:
      • Characterized by both propulsive and non-propulsive contractions
      • Propulsive Pattern: Peristaltic waves propel chyme aborally (towards the anus)
        • Fastest in the duodenum
        • Moderate speed in the jejunum
        • Slowest in the ileum
      • Non-Propulsive Pattern: Segmentation contractions
        • Localized contractions of circular muscle divide the intestine into constricted and dilated segments
        • Promotes mixing and nutrient absorption
        • Does not contribute to significant aboral propulsion
    • Interdigestive Phase:
      • Occurs when the stomach and small intestine are empty (between meals)
      • Characterized by the "Migrating Motoric Complex" (MMC)
        • Sweeps undigested material towards the colon
        • Regulates bacterial population and growth

    Migrating Motor Complex (MMC)

    • Comprises three phases characterized by distinct contraction patterns
    • Phase 1: Resting phase - no contractions.
    • Phase 2: Intermittent and irregular contractions, characterized by varying strengths.
    • Phase 3: Strong peristaltic contractions originating in the stomach and moving distally.

    Large Intestine Motility

    • Peristaltic waves move ingesta forward.
    • Antiperistaltic waves move ingesta backward, leading to more intense mixing.

    Pathologic Contractions

    • Oral migrating contractions cause vomiting.
      • A defense mechanism that eliminates gastrointestinal content.
      • Uses striated muscle and non-digestive structures coordinated by the brainstem.
    • Aboral migrating contractions cause diarrhea.
      • Increases the frequency or volume of defecation, often due to increased water content.
      • Occurs when there is a mismatch between water secretion and absorption.

    Causes and Sequence of Vomiting

    • Causes include:
      • Stimuli before food intake (smell, emotions, appearance).
      • Stimuli after food intake (visceral afferents to the vomiting center).
      • Stimuli after absorption (drugs and toxins stimulate the chemoreceptor trigger zone).
    • Sequence of events:
      • Antiperistaltic waves from the duodenum propel ingesta toward the stomach.
      • Contraction of the abdominal musculature increases intra-abdominal pressure.
      • Expansion of the chest cavity with a closed glottis lowers intrathoracic pressure.
      • The lower esophageal sphincter relaxes.
      • The upper esophageal sphincter opens.

    Types of Diarrhea

    • Malabsorptive Diarrhea:
      • Inadequate absorption of secreted water.
      • Can be caused by viral, bacterial, or protozoan infections.
      • Destruction of villi and reduced length lead to decreased surface area and less absorption.
    • Secretory Diarrhea:
      • Increased intestinal secretion overwhelms absorptive capacity.
      • Caused by enterotoxins.
      • No destruction of villi, but interference with absorption.

    Defecation Reflex

    • Involves the internal (smooth muscle) and external (striated muscle) sphincters.
    • Internal Sphincter:
      • Para- and sympathetic innervation.
      • Normally tonically contracted, providing continence.
    • External Sphincter:
      • Voluntarily constricted, allowing for potty training.
    • Rectosphincteric Reflex:
      • Feces accumulate in the rectum, a reservoir.
      • Peristaltic movement of feces into the rectum leads to relaxation of the internal sphincter.
      • Triggers the urge to defecate.

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    Description

    Explore the fascinating world of gastrointestinal reflexes that regulate various bodily functions. This quiz covers intrinsic, extrinsic, and central reflexes, including examples like the gastrocolic and enterogastric reflexes. Test your knowledge on how these reflexes impact digestion and gut health.

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