Gastric Acid Secretion and ECL Cells Quiz
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Questions and Answers

What stimulates the parietal cells to directly secrete acid during the cephalic phase of gastric secretion?

  • Release of gastrin-releasing peptide (GRP) from vagus nerves (correct)
  • Release of somatostatin
  • Release of ACh from nerve endings
  • Distention of the stomach

    • What is the main function of the antrum in the stomach?

  • Storage of food
  • Mixing and propulsion of food (correct)
  • Initiation of receptive relaxation
  • Secretion of alkaline mucus

    • Which phase of gastric secretion is primarily stimulated by the presence of food in the stomach?

  • Cephalic phase
  • Gastric phase (correct)
  • Intestinal phase
  • Postprandial phase

    • What is the effect of protein digestion products in the duodenum on gastric acid secretion?

    <p>Stimulate acid secretion through the action of circulating amino acids on parietal cells</p> Signup and view all the answers

    What is Zollinger-Ellison syndrome characterized by?

    <p>Excessive production of gastrin hormone leading to increased acidity secretions</p> Signup and view all the answers

    What are the glands lining the stomach wall?

    <p>Chief cells</p> Signup and view all the answers

    What is the mechanism of HCl secretion by parietal cells?

    <p>$H^+ + Cl^- \rightarrow HCl$</p> Signup and view all the answers

    What is the source of histamine that stimulates gastric acid secretion?

    <p>Enterochromaffin like (ECL) cells</p> Signup and view all the answers

    Which cells are primarily located in the acid-secreting regions of the stomach?

    <p>Enterochromaffin like (ECL) cells</p> Signup and view all the answers

    Which phase of gastric secretion is associated with the sight, smell, and taste of food?

    <p>Cephalic phase</p> Signup and view all the answers

    What is the role of pepsin in digestion?

    <p>Breaks down proteins into smaller polypeptides</p> Signup and view all the answers

    What controls stomach emptying?

    <p>$Cholecystokinin$</p> Signup and view all the answers

    What is the only essential function of the stomach as it is essential for vitamin B12 absorption?

    <p>Intrinsic Factor (IF) secretion</p> Signup and view all the answers

    What is the pathophysiologic basis of peptic ulcer and gastritis?

    <p>Inadequate mucus production in the stomach lining</p> Signup and view all the answers

    At a low secretion rate, gastric juice contains high concentrations of which electrolytes?

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

    What is the function of the pyloric sphincter in the stomach?

    <p>To prevent food particles larger than 2mm from leaving the stomach</p> Signup and view all the answers

    What happens to food particles larger than 2mm in the stomach?

    <p>They are tumbled back into the antrum for further degradation</p> Signup and view all the answers

    What is the role of the peristaltic wave in the stomach?

    <p>To mix food with digestive juices</p> Signup and view all the answers

    What is chyme in the context of stomach function?

    <p>A clear liquid composed of gastric secretions</p> Signup and view all the answers

    How does food leave the stomach via the pyloric sphincter?

    <p>It should be smaller than 2mm in size</p> Signup and view all the answers

    Which cells are responsible for secreting HCL across parietal cells and into the lumen of the stomach?

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

    What is the primary function of parietal cells in the stomach?

    <p>Secreting HCL</p> Signup and view all the answers

    What stimulates H2 receptors on parietal cells to increase HCL secretion?

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

    What is the primary component of gastric juice?

    <p>$H^+$ and $Cl^-$</p> Signup and view all the answers

    What is the role of carbonic anhydrase in the stomach?

    <p>Converting $HCO_3^-$ to $H_2CO_3$</p> Signup and view all the answers

    Which part of the stomach contains mainly Pyloric and G cells?

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

    Where is the gastric pacemaker region located?

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

    Which cells primarily produce mucus to protect the stomach from acid and digestive juices?

    <p>Mucus cells</p> Signup and view all the answers

    What is the function of the pylorus in the stomach?

    <p>Regulating the emptying of chyme into the small intestine</p> Signup and view all the answers

    What type of muscles make up the stomach wall?

    <p>Outer longitudinal, middle circular, inner oblique muscles</p> Signup and view all the answers

    What is the primary role of parietal cells in the stomach?

    <p>Secreting HCL across parietal cells and into the lumen</p> Signup and view all the answers

    What stimulates H2 receptors on parietal cells to increase HCL secretion?

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

    Which cells primarily produce mucus to protect the stomach from acid and digestive juices?

    <p>Surface mucous cells</p> Signup and view all the answers

    What is the primary function of parietal cells in the stomach?

    <p>Secrete hydrochloric acid (HCl) into the lumen of the stomach</p> Signup and view all the answers

    What stimulates H2 receptors on parietal cells to increase HCl secretion?

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

    What is the source of K+ for exchange with H+ in parietal cells?

    <p>Cell cytoplasm and basolateral membrane</p> Signup and view all the answers

    Which phase of gastric secretion is primarily stimulated by the presence of food in the stomach?

    <p>Gastric phase</p> Signup and view all the answers

    What are the glands lining the stomach wall?

    <p>Parietal glands, chief glands, enteroendocrine glands</p> Signup and view all the answers

    What is the source of histamine that stimulates gastric acid secretion?

    <p>Enterochromaffin-like (ECL) cells in the gastric mucosa</p> Signup and view all the answers

    What is chyme in the context of stomach function?

    <p>$pH &lt; 2.0$ thick, acidic mixture of food and digestive enzymes</p> Signup and view all the answers

    What is the size requirement for food particles to leave the stomach via the pyloric sphincter?

    <p>Less than 2mm</p> Signup and view all the answers

    What is the primary mechanism for movement of chyme into the duodenum?

    <p>Pyloric pump</p> Signup and view all the answers

    What happens if food particles are larger than 2mm in the stomach?

    <p>They are tumbled back into the antrum for further degradation</p> Signup and view all the answers

    What is the composition of chyme in the context of stomach function?

    <p>Murky semi-fluid or paste composed of food mixed with gastric secretions</p> Signup and view all the answers

    What initiates the leading contraction in squeezing food down in the stomach?

    <p>$\text{Peristaltic wave}$ passing from antrum to pylorus</p> Signup and view all the answers

    What triggers the cephalic phase of gastric secretion?

    <p>Sight, smell, and taste of food</p> Signup and view all the answers

    What is the primary mediator of the cephalic phase of gastric secretion?

    <p>Vagus nerve</p> Signup and view all the answers

    What triggers the gastric phase of HCL secretion?

    <p>Distention and chemical stimuli in the stomach</p> Signup and view all the answers

    What accounts for minimal stimulation of HCL secretion in the stomach?

    <p>Intestinal phase</p> Signup and view all the answers

    What triggers the mixing/propulsion waves in the stomach?

    <p>Gut wall's basic electrical rhythm</p> Signup and view all the answers

    Which region of the stomach is responsible for generating slow waves leading to contractions?

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

    Which part of the stomach contains mainly Parietal and Chief cells?

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

    What is the primary function of the pylorus in the stomach?

    <p>Regulating the emptying of chyme into the small intestine</p> Signup and view all the answers

    Which cells primarily produce mucus to protect the stomach from acid and digestive juices?

    <p>Mucus cells</p> Signup and view all the answers

    What type of muscles make up the stomach wall?

    <p>Outer circular, middle longitudinal, inner oblique muscles</p> Signup and view all the answers

    Which of the following cells release somatostatin, secretin, and glucose-dependent insulinotropic peptide (GIP) to inhibit acid secretion in the stomach?

    <p>D cells</p> Signup and view all the answers

    What is the primary function of intrinsic factor (IF) secreted by parietal cells in the stomach?

    <p>Necessary for vitamin B12 absorption</p> Signup and view all the answers

    Which of the following hormones indirectly stimulates gastrin release from G cells to increase HCl secretion in the stomach?

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

    What is the main function of mucus in the stomach?

    <p>Protecting the stomach from damage by acid and forming a barrier for the gastric surface</p> Signup and view all the answers

    Which of the following is responsible for modifying gastric juice's composition based on the secretion rate?

    <p>Parietal cells</p> Signup and view all the answers

    What is the primary mechanism for allowing food to enter the stomach and increase its volume without a significant increase in pressure?

    <p>Receptive relaxation</p> Signup and view all the answers

    What is the maximum amount of food that the stomach can store?

    <p>1.5 L</p> Signup and view all the answers

    Which reflex is triggered by swallowing and allows the stomach to relax as food enters, facilitating storage?

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

    What is the function of receptive relaxation in the stomach?

    <p>To allow food to enter and increase stomach volume without increasing pressure</p> Signup and view all the answers

    What triggers a reduction in muscular wall tone in the stomach, allowing for storage of food?

    <p>$Vagovagal$ reflex</p> Signup and view all the answers

    What is the primary function of mixing propulsion of food in the stomach?

    <p>To transform food into a form that can pass through the pylorus and be easily dealt with by the intestine</p> Signup and view all the answers

    What is the primary function of the antrum in the stomach?

    <p>Initiating weak peristaltic constrictor waves</p> Signup and view all the answers

    What triggers hunger contractions in the stomach?

    <p>Long-term fasting</p> Signup and view all the answers

    What is the primary role of adaptive relaxation in the stomach?

    <p>Accommodating greater quantities of food</p> Signup and view all the answers

    What is the effect of loss of adaptive relaxation in patients undergoing vagotomy?

    <p>Impaired mixing and movement of chyme towards pylorus</p> Signup and view all the answers

    What happens to food particles larger than 2mm in the stomach?

    <p>They are forced back into the antrum to be further degraded</p> Signup and view all the answers

    When does the stomach relax during digestion?

    <p>In the presence of nutrients in the small intestine</p> Signup and view all the answers

    What initiates adaptive relaxation in the stomach?

    <p>Stretch receptors</p> Signup and view all the answers

    What triggers the antral contractions responsible for stomach emptying?

    <p>Ca$^{2+}$ influx triggering two types of contractions</p> Signup and view all the answers

    What is the primary role of the pylorus in stomach emptying?

    <p>Control point influenced by nervous and humoral reflux signals</p> Signup and view all the answers

    What is the frequency of action potentials generated by the pacemaker region?

    <p>Three per minute</p> Signup and view all the answers

    What triggers the two types of contractions in the stomach due to the long duration of the action potential?

    <p>$Ca^{2+}$ influx</p> Signup and view all the answers

    What facilitates propagation of action potentials in the gastric musculature?

    <p>$Ca^{2+}$ influx</p> Signup and view all the answers

    What phenomenon results from activation of the vomiting center during antral contractions?

    <p>Retropulsion phenomena</p> Signup and view all the answers

    What is responsible for decreased compliance of the gastric wall after vagotomy?

    <p>Pressure-volume curves</p> Signup and view all the answers

    What is the primary role of the hormone gastrin in stomach function?

    <p>Stimulates the release of gastric juices and enhances stomach emptying</p> Signup and view all the answers

    What triggers enterogastric nervous reflexes that inhibit stomach emptying?

    <p>Release of inhibitory hormones such as Cholecystokinin (CCK)</p> Signup and view all the answers

    What stimulates the release of Glucose-dependent insulinotropic polypeptide (GIP) in females?

    <p>Enterogastric reflex initiated by the duodenum</p> Signup and view all the answers

    What percentage of consumed starch does the stomach digest?

    <p>$30-40%$</p> Signup and view all the answers

    Where does the remaining digestion occur for food partially digested by the stomach?

    <p>Small intestine</p> Signup and view all the answers

    Which factor directly promotes stomach emptying?

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

    What inhibits stomach emptying through direct routes from the duodenum?

    <p>Inhibitory hormones such as Cholecystokinin (CCK)</p> Signup and view all the answers

    What is released from the duodenum in response to food to inhibit stomach emptying?

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

    What is a function shared by both the stomach and duodenum?

    <p>Digest and absorb nutrients from food.</p> Signup and view all the answers

    Study Notes

    • Stomach is a J-shaped organ located in the upper left side of the abdomen, responsible for storing and digesting food.

    • Anatomically, the stomach consists of the following parts: Fundus, Antrum, Body, Caudad (Antral Pump), and Upper region. The lower third of the body plus the antrum and pylorus is called the caudad region, while the upper half is called the orad region.

    • The stomach wall is composed of three layers: outer longitudinal, middle circular, and inner oblique muscles. The muscle thickness increases as we move from the proximal to distal regions.

    • The gastric pacemaker region is located at the upper part of the stomach, where slow waves are generated, leading to contractions.

    • The gastric mucosa is formed of columnar epithelium folded into "pits," which are the openings of gastric glands. Gastric glands are distributed differently throughout the stomach, with different types found in specific regions.

    • The pylorus is a slightly tonically contracted region, acting as a sphincter, which is controlled by nervous and hormonal reflexes.

    • The stomach has several functions: Storage of large food quantities, preparing chyme for digestion, absorption of water and lipid-soluble substances, and regulating the emptying of the chyme into the small intestine.

    • The gastric glands secrete various substances, such as mucus, hydrochloric acid (HCl), pepsinogen, intrinsic factor (IF), and gastrin.

    • The stomach lining is lined by various cell types, including: Mucus cells, Parietal cells (Oxyntic cells), Chief cells (Peptic cells), Enteroendocrine cells, and G cells. The distribution and functions of these cells vary throughout the stomach.

    • Oxyntic glands are the most abundant gastric glands in the fundus and corpus (body), containing both Parietal and Chief cells.

    • The pylorus, the lower part of the antrum and pylorus, contains mainly Pyloric and G cells. The functions of the cells vary, with Parietal cells producing HCl and IF, and Chief cells secreting pepsinogen.

    • The neck region of the gastric glands contains mucus cells, which produce mucus to protect the stomach from acid and digestive juices.

    • Gastric glands secrete specific substances to aid in the digestion and absorption process.

    • The stomach functions as a storage tank, a mixing chamber, and a churning mechanism, transforming food into chyme before it enters the small intestine.

    • Enterochromaffin-like (ECL) cells in the stomach release histamine, stimulating gastric acid secretion. Their activation mechanisms are not well understood.

    • Histamine activates H2 receptors on parietal cells, increasing hydrochloric acid (HCl) secretion. H2 blockers, like cimetidine, reduce acid secretion, demonstrating histamine's role in gastric acid secretion.

    • Vagus nerve acetylcholine (Ach) acts directly on parietal cells to increase HCl secretion. Indirectly, Ach stimulates gastrin release from G cells, which acts on parietal cells' CCKB receptors to increase HCl secretion.

    • Histamine (paracrine secretion) and gastrin (endocrine secretion) both increase HCl secretion. H2 receptors on parietal cells are activated by histamine, while gastrin binds to receptors on parietal cells, directly stimulating acid secretion.

    • D cells in the antrum and corpus release somatostatin, secretin, and glucose-dependent insulinotropic peptide (GIP), which inhibit acid secretion.

    • Mucus covers the stomach's mucosa, protecting it from damage by acid and forming a barrier for the gastric surface, which is rich in bicarbonate.

    • Pepsinogen, which is secreted by chief cells, is converted into pepsin by HCl. Pepsin breaks down proteins into smaller peptides and polypeptides, activating more pepsinogen in the process. It is essential for protein digestion and stimulates gastrin release.

    • Parietal cells secrete intrinsic factor (IF), a glycoprotein necessary for vitamin B12 absorption. Damage to parietal cells can lead to pernicious anemia, as B12 can't be absorbed without IF.

    • Gastric juice's composition is modified based on the secretion rate. At a low secretion rate, gastric juice contains high concentrations of sodium (Na+) and chloride (Cl-) and low concentrations of potassium (K+) and hydrochloric acid (H+). As the secretion rate increases, H+ concentration significantly increases, and Cl- concentration increases. The secretions of parietal cells, which contribute mainly to the changes in electrolyte composition, are responsible for these changes.

    • The stomach transforms food into a semi-liquid mix called "chyme" through mixing activities in the antrum

    • Weak peristaltic constrictor waves called mixing/constrictor waves initiate from the stomach wall's basic electrical rhythm and force the chyme to mix and move towards the pylorus

    • Food particles larger than 2mm cannot pass through the pyloric sphincter and are forced back into the antrum to be further degraded

    • The stomach stores food in the upper part (reservoir) and mixes it in the lower part (mixing and grinding)

    • Hunger contractions occur when the stomach has been empty for several hours and are more frequent in young, healthy individuals

    • The stomach has a poor absorptive capacity and relaxes during swallowing and the presence of nutrients in the small intestine

    • Adaptive relaxation, triggered by stretch receptors, allows the stomach to accommodate greater quantities of food and delay gastric emptying

    • The text notes that adaptive relaxation is lost in patients undergoing vagotomy.

    • The hormone gastrin, released from the antral mucosa in response to the presence of digestive products of meat, activates oxyntic cells to secrete gastric juices (HCl) and enhances the activity of the pyloric pump and motor stomach function, promoting stomach emptying.

    • The presence of food in the stomach causes distension, triggering neural responses by the Vagus nerve and the Enteric Nervous System, which increase the motility of the stomach and promote stomach emptying.

    • Proteins in the food stimulate the release of gastrin.

    • Gastric factors that promote emptying include distension and proteins.

    • The duodenum, upon receiving food, initiates enterogastric nervous reflexes that inhibit stomach emptying through three routes: directly from the duodenum to the stomach, through extrinsic nerves to the prevertebral sympathetic ganglia, and through the vagus nerves.

    • The duodenum releases inhibitory hormones such as Cholecystokinin (CCK) in response to fat or acidity of chyme or excess quantities, leading to decreased stomach emptying.

    • The duodenum also releases other inhibitory hormones such as secretin and gastric inhibitory peptide (GIP) in response to food.

    • In females, the duodenum initiates an Enterogastric reflex, which decreases stomach emptying, and stimulates the release of Glucose-dependent insulinotropic polypeptide (GIP) in response to carbohydrates.

    • The stomach digests 30-40% of consumed starch and some fat.

    • The duodenum receives food that is already partially digested by the stomach, with the remaining digestion occurring in the small intestine.

    • The duodenum receives and processes carbohydrates, fats, and proteins from the diet.

    • The stomach and duodenum work together to digest and absorb nutrients from food.

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    Description

    Test your knowledge about the mechanisms of gastric acid secretion and the role of enterochromaffin-like (ECL) cells in histamine release. Explore the impact of H2 blockers on acid secretion.

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