Stomach Structure and Function Quiz

Stomach Structure and Function

• The stomach is an enlarged portion of the digestive tract, storing 1.5-2 liters of ingested food.
• Its wall contains three layers of muscle.
• The stomach has four main parts: cardia, fundus, body, and pylorus (pyloric antrum, pyloric canal, pyloric sphincter).
• The stomach's curved shape defines 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 (inactive form of pepsin) and gastric lipase.
• G cells: Secrete gastrin hormone.

Stomach Motility and Chyme

• The stomach mixes ingested food with gastric juice via mixing waves (not peristaltic waves).
• The resulting mixture of food and gastric juice is called chyme.
• Gastric juice breaks down food, making it more liquid.

Stomach Acid Secretion and Enzyme Activation

• Stomach acid (HCl) inactivates salivary amylase but activates lingual lipase, which begins triglyceride digestion.
• The proton pump (H+/K+ pump) actively transports hydrogen ions into the stomach lumen.
• This process uses ATP and creates an "alkaline tide", since bicarbonate ions enter circulation.
• Stomach acid kills microorganisms, denatures proteins, and stimulates the release of bile and pancreatic juice.

Protein Digestion in Stomach

• The stomach secretes pepsin, a protein-digesting enzyme, from chief cells.
• Pepsinogen (inactive form of pepsin) is initially secreted, becoming active in acidic conditions (low pH).
• Activation is triggered by HCl or pre-existing active pepsin.

Lipid Digestion in Stomach

• The stomach also secretes gastric lipase to continue lipid digestion.
• Optimal pH for gastric lipase activity (5-6). Pancreatic lipase becomes more important for efficient lipid breakdown.

Acid Secretion Mechanism

• Carbonic anhydrase in parietal cells converts carbon dioxide and water to carbonic acid.
• Carbonic acid then dissociates into bicarbonate ions and hydrogen ions.
• Hydrogen ions are actively transported into the stomach lumen via the H+/K+ ATPase pump.
• Chloride ions passively diffuse into the lumen, combining with the hydrogen ions to form HCl acid.
• Bicarbonate ions leave the parietal cells to the blood, creating an alkaline tide.