During the gastric phase of digestion

Correct Answer: C

Rationale: Rationale: 1. Gastric phase starts when food enters the stomach. 2. Chemoreceptors detect bolus composition to initiate gastric secretions. 3. This detection triggers release of gastric juices for digestion. 4. Neural stimulation also occurs during gastric phase, but not exclusively. 5. Contractility increases during gastric phase for mixing and churning. In summary, choice C is correct as chemoreceptors detect bolus composition during the gastric phase, while the other choices are incorrect because they do not accurately reflect the physiological processes during this phase.

Correct Answer: B

Rationale: The correct answer is B because the normal concentration of bilirubin in the plasma is about 0.8 gm%, which is a commonly accepted fact in medicine. Bilirubin is a product of hemoglobin breakdown and is typically measured in the blood to assess liver function and detect certain medical conditions. A, C, and D are incorrect: A: Myenteric plexus controls GIT motility, not secretion. C: Submucosal plexus controls GIT secretion, not motility. D: Pepsinogen activation needs hydrochloric acid (HCl) in the stomach, not calcium.

Correct Answer: B

Rationale: Step 1: CCK (Cholecystokinin) is released in response to the presence of fats and proteins in the small intestine. Step 2: CCK inhibits stomach motility to allow enough time for the gallbladder to release bile. Step 3: This slowing down of stomach motility aids in the digestion and absorption of fats. Step 4: Choices A, C, and D are incorrect as CCK does not directly affect gastric secretion, pancreatic enzyme secretion, or increase pancreatic secretions rich in bicarbonate.

Correct Answer: D

Rationale: The correct answer is D, Cholecystokinin (CCK). CCK is produced in the small intestine in response to the presence of fats and proteins. It stimulates the release of digestive enzymes from the pancreas to aid in digestion. Insulin (A) and Glucagon (B) are involved in regulating blood sugar levels, not digestive enzyme release. Secretin (C) primarily stimulates the release of bicarbonate from the pancreas to neutralize stomach acid, not digestive enzymes.

Correct Answer: B

Rationale: The correct answer is B: peristalsis. Peristalsis is the coordinated, rhythmic muscle contractions that propel food through the esophagus and digestive tract. This process helps move food downward towards the stomach. Gravity (choice A) is not the primary mechanism for moving food through the esophagus. Rugae (choice C) refers to folds in the stomach lining, not muscle action in the esophagus. Chyme (choice D) is the partially digested food mixed with stomach acids and enzymes, not a process of moving food down the esophagus. Therefore, peristalsis is the correct answer as it accurately describes the muscle action involved in pushing food downward through the esophagus.