Gastrointestinal Physiology Quiz
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Questions and Answers

What primarily determines the rate of gastric emptying?

  • Temperature of the chyme
  • Consistency of chyme
  • Presence of bile in the stomach
  • Strength of antral wave and pyloric sphincter opening (correct)

    • Which factor is NOT associated with gastric emptying?

  • Thickness of stomach wall (correct)
  • Stretch of smooth muscle
  • Gastrin release
  • Duodenal hormone response

    • Which substance is particularly potent in delaying gastric emptying?

  • Carbohydrates
  • Protein
  • Water
  • Fat (correct)

    • What is the role of enterogastrones released from the duodenum?

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

    What occurs when the duodenum is not ready to receive chyme?

    <p>Decreased antral activity</p> Signup and view all the answers

    What is the role of H+/K+ ATPase in parietal cells?

    <p>It transports H+ ions into the gastric lumen.</p> Signup and view all the answers

    Which neurotransmitter is released by parasympathetic cholinergic neurons to stimulate parietal cells?

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

    How does gastrin affect parietal cells?

    <p>It activates PLC upon binding to CCK2 receptors.</p> Signup and view all the answers

    What is the source of histamine in the gastric glands?

    <p>Enterochromaffin-like cells</p> Signup and view all the answers

    Which cellular process occurs when parietal cells are stimulated?

    <p>Activation of PLC leading to acid secretion.</p> Signup and view all the answers

    Which factor does NOT stimulate histamine secretion?

    <p>Increased CO2 levels</p> Signup and view all the answers

    What mechanism initiates the transport of H+ into the gastric lumen by parietal cells?

    <p>Binding of acetylcholine to muscarinic receptors.</p> Signup and view all the answers

    What effect does the activation of PLC have on parietal cells?

    <p>Increases H+ secretion.</p> Signup and view all the answers

    What area of the stomach is primarily responsible for producing hydrochloric acid?

    <p>Oxyntic mucosa</p> Signup and view all the answers

    What is the role of pepsinogen in the stomach?

    <p>It serves as an inactive precursor of pepsin.</p> Signup and view all the answers

    Which cell type in the gastric glands is primarily responsible for producing gastrin?

    <p>G cell</p> Signup and view all the answers

    What function does hydrochloric acid (HCl) serve in the gastric secretions?

    <p>It denatures protein.</p> Signup and view all the answers

    Identifying the components of gastric mucosa, which area includes the chief cells?

    <p>Oxyntic mucosa</p> Signup and view all the answers

    The pyloric gland area is specifically located in which part of the stomach?

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

    What does somatostatin do in the context of gastric secretions?

    <p>Inhibits gastrin secretion.</p> Signup and view all the answers

    Which of the following is NOT a component of the gastric mucosa?

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

    What is the role of the vagus nerve in gastric function?

    <p>It stimulates parietal cells directly through ACh.</p> Signup and view all the answers

    How does gastrin affect parietal cells?

    <p>It stimulates them via endocrine action.</p> Signup and view all the answers

    Which of the following mechanisms does NOT contribute to the stimulation of parietal cells?

    <p>Direct action of GRP on parietal cells.</p> Signup and view all the answers

    What triggers the activation of enteric neurones through mechanoceptors?

    <p>Distension of the stomach.</p> Signup and view all the answers

    Which neurotransmitter is directly released by enteric neurones to stimulate parietal cells?

    <p>Acetylcholine (ACh).</p> Signup and view all the answers

    What is the function of somatostatin in this context?

    <p>It inhibits the action of G cells.</p> Signup and view all the answers

    How does the presence of food affect gastric phase activity?

    <p>It triggers both chemical and mechanical responses.</p> Signup and view all the answers

    Which cell is primarily responsible for the release of histamine in the stomach?

    <p>ECL cell.</p> Signup and view all the answers

    Which aspect is NOT directly related to the gastric phase of digestion?

    <p>Somatic muscle contraction.</p> Signup and view all the answers

    What is the role of GRP in gastric function?

    <p>It promotes gastrin release from G cells.</p> Signup and view all the answers

    What is the primary function of HCO3- in the duodenum?

    <p>To neutralize acidic chyme</p> Signup and view all the answers

    Which transporter is responsible for HCO3- secretion at the basolateral membrane of pancreatic duct cells?

    <p>Na+/Cl- cotransporter/HCO3- exchanger</p> Signup and view all the answers

    What is a possible consequence of cystic fibrosis concerning pancreatic duct cells?

    <p>Reduced fluid secretion</p> Signup and view all the answers

    What role does Cl- play in HCO3- secretion at the apical membrane?

    <p>Cl- is exchanged for HCO3-</p> Signup and view all the answers

    What is the effect of HCO3- on pancreatic enzyme function?

    <p>It provides an optimum pH for their function</p> Signup and view all the answers

    At what secretion rates is the HCO3- content highest?

    <p>At high secretion rates</p> Signup and view all the answers

    Which mechanism describes the entry of Na+ into pancreatic duct cells?

    <p>Na+/Cl- cotransporter</p> Signup and view all the answers

    What happens to H2CO3 in the pancreatic duct cells?

    <p>It is converted into HCO3- and H+</p> Signup and view all the answers

    Study Notes

    Parietal Cell Stimulation and HCl Secretion

    • The parietal cell is stimulated by three main mechanisms:
      • Acetylcholine (ACh) released from parasympathetic cholinergic neurons binds to muscarinic (M3) receptors on parietal cells, leading to the activation of phospholipase C (PLC).
      • Gastrin released from G cells binds to CCK2 receptors on parietal cells, also activating PLC.
      • Histamine secreted by enterochromaffin-like (ECL) cells in the gastric glands is stimulated by acetylcholine and locally activates parietal cells.
    • When stimulated, the parietal cell transports H+ into the gastric lumen using the H+/K+ ATPase on the apical membrane.

    Control of Stomach Emptying

    •  Gastric emptying is controlled by the strength of the antral wave and the opening of the pyloric sphincter.
    • The rate of gastric emptying depends on the volume of chyme in the stomach.
      • Distension of the stomach increases motility, due to:
        • Stretch of smooth muscle
        • Stimulation of intrinsic nerve plexuses
        • Increased vagus nerve activity and gastrin release.
    • The consistency of chyme influences emptying, with thin liquid chyme being emptied faster.

    ### Duodenal Factors Affecting Emptying

    • The duodenum regulates the rate of emptying by delaying it when not ready to receive chyme.
    • This delay is mediated by:
      • Enterogastric reflex: Neuronal signals from intrinsic nerve plexuses and the autonomic nervous system (ANS) decrease antral activity.
      • Hormonal response: Enterogastrones like cholecystokinin (CCK) released from the duodenum inhibit stomach contraction.
    • Stimuli in the duodenum that trigger these responses include:
      • Fat: Fat delays gastric emptying to allow time for digestion and absorption in the small intestine.
      • Acid: Time is needed for neutralization of gastric acid by pancreatic bicarbonate, crucial for proper function of pancreatic enzymes.
      • Hypertonicity: Digestion products of carbohydrates and proteins are osmotically active, drawing water into the small intestine. This can lead to reduced plasma volume and dangerous circulatory disturbances, like 'dumping syndrome'.
      • Distension: Duodenal distension also contributes to the control of gastric emptying.

    Gastric Mucosa

    • The gastric mucosa is divided into two regions:
      • Oxyntic gland area (OM): Proximal stomach, including the fundus and body.
      • Pyloric gland area (PGA): Distal stomach, also known as the antrum.
    • The gastric mucosa is composed of three layers:
      • Surface lining: Lines the stomach.
      • Pits: Invaginations of the surface lining.
      • Glands: At the base of the pits, responsible for secretion.

    Gastric Secretions

    • Different cell types within the gastric glands produce various secretions:
      • Oxyntic mucosa:
        • Parietal cells: Produce HCl, intrinsic factor, and gastroferrin.
        • Chief cells: Produce pepsinogen.
      • Pyloric gland area:
        • G cells: Produce gastrin.
        • D cells: Produce somatostatin.
        • Enterochromaffin-like (ECL) cells: Produce histamine.

    Functions of Gastric Secretions

    • HCl:
      • Activates pepsinogen to pepsin.
      • Denatures proteins.
      • Kills most microorganisms ingested with food.
    • Pepsinogen: Inactive precursor of the peptidase, pepsin.

    Regulation of Gastric Secretion

    • The vagus nerve stimulates enteric neurons, which in turn:
      • Release acetylcholine (ACh) directly activating parietal cells (neurotransmitter action).
      • Release gastrin-releasing peptide (GRP), leading to the release of gastrin from G cells into the systemic circulation, activating parietal cells (endocrine action).
      • Release histamine from ECL cells, locally activating parietal cells (paracrine action).
      • Inhibit D cells, reducing the inhibitory effect of somatostatin (SS) on G cells.

    Gastric Phase of Digestion

    •  The gastric phase is triggered by:
      • Distension of the stomach.
      • Protein digestion products.
      • Smell and taste of food.
    • This phase leads to the release of ACh, gastrin, and histamine, stimulating the secretion of HCl and pepsinogen.

    Pancreatic Duct Cell Secretion

    • Pancreatic duct cells are responsible for secreting bicarbonate (HCO3-), which is essential for neutralizing acidic chyme entering the duodenum.
    • This neutralization:
      • Provides the optimal pH for pancreatic enzyme function.
      • Protects the mucosa from erosion by acid.
    • HCO3- secretion occurs via a Cl-/HCO3- exchanger at the apical membrane facing the lumen of the pancreatic duct.
    • Na+/K+ ATPase at the basolateral membrane facing the interstitium contributes to the supply of HCO3-.
    • Some HCO3- secretion might also occur via the cystic fibrosis transmembrane conductance regulator (CFTR), although not depicted in the figure provided.
    • Patients with cystic fibrosis, lacking functional CFTR, have reduced fluid secretion.

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    Description

    Test your understanding of parietal cell stimulation and HCl secretion, as well as the control of stomach emptying. This quiz covers key mechanisms and physiological processes involved in digestion. Prepare to explore important concepts related to gastric functions and the factors affecting them.

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