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Questions and Answers
What is the main function of the surface mucous cells in the stomach?
What is the main function of the surface mucous cells in the stomach?
Which part of the stomach is responsible for the secretion of HCl and intrinsic factor?
Which part of the stomach is responsible for the secretion of HCl and intrinsic factor?
What role does carbonic anhydrase play in the function of parietal cells in the stomach?
What role does carbonic anhydrase play in the function of parietal cells in the stomach?
What is chyme?
What is chyme?
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Which type of cell is primarily responsible for secreting pepsinogen?
Which type of cell is primarily responsible for secreting pepsinogen?
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How does the acidic environment of the stomach affect salivary amylase?
How does the acidic environment of the stomach affect salivary amylase?
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What structure prevents the backflow of chyme from the duodenum into the stomach?
What structure prevents the backflow of chyme from the duodenum into the stomach?
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Which hormone secreted by G cells stimulates gastric acid secretion?
Which hormone secreted by G cells stimulates gastric acid secretion?
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Which ion is actively exported from the parietal cells of the stomach into the lumen?
Which ion is actively exported from the parietal cells of the stomach into the lumen?
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What is the significance of pepsinogen being released in an inactive form?
What is the significance of pepsinogen being released in an inactive form?
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Study Notes
Stomach Anatomy and Function
- The stomach holds approximately 1.5-2 liters of ingested food.
- It has three layers of muscle tissue.
- The stomach has four major parts: cardia, fundus, body, and pylorus (pyloric antrum, pyloric canal, pyloric sphincter).
- Stomach's curved shape gives rise to greater and lesser curvatures.
- The stomach lining (mucosa) has folds called rugae.
Stomach Glandular Cells
- Surface mucous cells: Secrete mucus.
- Mucous neck cells: Secrete mucus, found deeper in gastric pits.
- Parietal cells: Secrete hydrochloric acid (HCl) and intrinsic factor (for vitamin B12 absorption).
- Chief cells: Secrete pepsinogen (an inactive form of pepsin) and gastric lipase.
- G cells: Secrete the hormone gastrin.
Stomach Function and Processes
- The stomach mixes ingested food with gastric juice through mixing waves (not peristaltic waves).
- Gastric juice dissolves food, making it more liquid (chyme).
- Acidic stomach secretions inactivate salivary amylase but activate lingual lipase, the beginning of lipid digestion..
- Stomach acid (HCl) kills many microorganisms and denatures proteins it also stimulates the release of bile and pancreatic juice.
- Protein digestion begins with pepsin, an enzyme secreted as pepsinogen (in its inactive form) by chief cells. Pepsin requires an acidic environment for optimal activity. Activation of pepsinogen happens through contact with HCl or already activated pepsin; this mechanism prevent the stomach from digesting itself.
HCL Secretion Mechanism
- HCL production utilizes a proton pump (actually an H+/K+ pump) and ATP energy.
- Potassium ions go into parietal cells, and hydrogen ions exit into stomach lumen through the H+/K+ pump.
- Chloride and potassium ions passively diffuse into the lumen.
- Carbonic anhydrase catalyses carbon dioxide and water to produce carbonic acid, which then dissociates into bicarbonate ions and hydrogen ions.
- Bicarbonate ions leave the cell, which is followed by alkaline tide (movement of alkaline bicarbonate into the circulatory system).
- Hydrogen ions are actively transported into the stomach lumen.
Lipid and Enzyme Details
- Gastric lipase is also produced by the stomach and plays a role in lipid digestion. However, its optimal pH range (5-6) isn't easily maintained which results in pancreatic lipase becoming a more crucial lipid degrading enzyme.
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Description
Test your knowledge on stomach anatomy including its structure, glandular cells, and physiological functions. This quiz covers topics such as the main parts of the stomach, types of cells, and the processes that occur within the stomach during digestion.
