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Questions and Answers
What is the primary function of parietal cells in the stomach?
What is the primary function of parietal cells in the stomach?
What term describes the mixture of ingested food and gastric juice in the stomach?
What term describes the mixture of ingested food and gastric juice in the stomach?
Which cells in the stomach are responsible for the production of mucus?
Which cells in the stomach are responsible for the production of mucus?
What is the role of the proton pump in gastric cells?
What is the role of the proton pump in gastric cells?
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Which stomach enzyme is responsible for protein digestion?
Which stomach enzyme is responsible for protein digestion?
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What structure allows passage of material from the stomach to the small intestine?
What structure allows passage of material from the stomach to the small intestine?
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What is the primary reason for the stomach's acidic environment?
What is the primary reason for the stomach's acidic environment?
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Which component of gastric juice helps in killing microorganisms?
Which component of gastric juice helps in killing microorganisms?
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Which layer of muscle is NOT present in the walls of the stomach?
Which layer of muscle is NOT present in the walls of the stomach?
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What is the role of bicarbonate ions in the context of stomach function?
What is the role of bicarbonate ions in the context of stomach function?
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Which part of the stomach is NOT considered one of its four major sections?
Which part of the stomach is NOT considered one of its four major sections?
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Which factor is essential for the activation of pepsin from its inactive form?
Which factor is essential for the activation of pepsin from its inactive form?
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What is the function of the rugae found in the stomach?
What is the function of the rugae found in the stomach?
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Which of the following hormones is secreted by G cells in the stomach?
Which of the following hormones is secreted by G cells in the stomach?
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What is the primary substance released by chief cells for lipid digestion?
What is the primary substance released by chief cells for lipid digestion?
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What is the effect of stomach acidity on salivary amylase?
What is the effect of stomach acidity on salivary amylase?
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Which part of the pylorus is directly leading into the duodenum?
Which part of the pylorus is directly leading into the duodenum?
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What is required for the carbonic anhydrase enzyme to function effectively?
What is required for the carbonic anhydrase enzyme to function effectively?
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Study Notes
Stomach Structure and Function
- The stomach is a dilated part of the digestive tract, with a capacity of 1.5 to 2 liters.
- Its walls contain three layers of muscle.
- The stomach has four main parts: cardia, fundus, body, and pylorus (pyloric antrum, pyloric canal, pyloric sphincter).
- Its shape gives rise to greater and lesser curvatures.
- The stomach lining (mucosa) has folds called rugae.
Stomach Glands and Secretions
- Surface mucous cells: secrete mucus.
- Mucous neck cells: secrete mucus, 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 the enzyme pepsin) and gastric lipase.
- G cells: secrete the hormone gastrin.
Stomach Mixing and Chyme
- The stomach creates mixing waves, not peristaltic waves, to mix food with gastric juice.
- This mixture of food and gastric juice is called chyme.
- Gastric juice dissolves food and makes it liquid.
Acidic Stomach Secretions
- Stomach acid inactivates salivary amylase.
- Stomach acid activates lingual lipase, which begins fat digestion.
- The potent acid (HCl) eliminates many microorganisms, unfolds proteins, and triggers hormonal responses for bile and pancreatic juice release.
Acid Production (Proton Pump)
- The stomach's proton pump is actually an H+/K+ pump, using ATP.
- It imports potassium and exports hydrogen ions into the stomach lumen.
- Parietal cells permit chloride and potassium to diffuse into the lumen.
- Carbonic anhydrase catalyzes the reaction of water and carbon dioxide to create carbonic acid, decomposing into bicarbonate and hydrogen ions.
- Bicarbonate leaves the cell, creating an alkaline tide in the bloodstream.
- Hydrogen ions are actively exported to the stomach.
Protein Digestion in the Stomach
- Pepsin, secreted by chief cells, digests proteins.
- Pepsin needs an acidic environment (low pH) for maximum activity.
- Pepsinogen is the inactive form of pepsin; it is activated by HCl or already-activated pepsin. This prevents self-digestion.
Lipid Digestion in the Stomach
- Gastric lipase continues lipid digestion.
- Its optimal pH is 5-6.
- Pancreatic lipase becomes the primary lipid-digesting enzyme due to the less easily attained optimal pH range.
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Description
Test your knowledge on the anatomy and physiology of the stomach, including its structure, glands, and the process of chyme formation. This quiz covers the main components and functions of the stomach essential for digestion.
