Which phase of deglutition involves contraction of the longitudinal muscle layer of the muscularis?

Correct Answer: D

Rationale: The correct answer is D: esophageal phase. During the esophageal phase of deglutition, the longitudinal muscle layer of the muscularis contracts to help propel the bolus of food downwards towards the stomach. This contraction occurs in a coordinated manner to create peristaltic waves that push the food along the esophagus. In contrast, the voluntary phase (A) involves the conscious initiation of swallowing, the buccal phase (B) involves the tongue pushing the bolus towards the pharynx, and the pharyngeal phase (C) involves the initiation of the swallowing reflex and closure of the airway to prevent aspiration.

Correct Answer: A

Rationale: The correct answer is A: gastrin. Gastrin is a hormone produced by G cells in the stomach lining that stimulates the release of gastric acid. It acts directly on parietal cells to increase acid secretion. Secretin (B) stimulates pancreatic bicarbonate secretion, not gastric acid. Insulin (C) regulates blood sugar levels, not gastric acid secretion. Cholecystokinin (D) stimulates the release of bile from the gallbladder and pancreatic enzymes, not gastric acid.

Correct Answer: C

Rationale: The correct answer is C: chemical digestion of starch. In the mouth, salivary glands secrete enzymes like amylase to break down starch into simpler sugars. This process initiates the digestion of carbohydrates. Mechanical digestion (Choice B) occurs in the mouth through chewing and mixing food with saliva, but it does not involve chemical breakdown. Chemical digestion of proteins (Choice A) primarily occurs in the stomach and small intestine with the help of enzymes like pepsin and trypsin. Choice D is incorrect because not all the processes listed occur in the mouth.

Correct Answer: B

Rationale: The correct answer is B: storing bile. The gallbladder functions to store bile produced by the liver and release it into the small intestine to aid in digestion. Bile helps in the breakdown of fats. Choices A, C, and D are incorrect because the gallbladder does not produce bile (the liver does), secrete digestive enzymes (pancreas does), or neutralize stomach acid (function of the stomach and duodenum).

Correct Answer: A

Rationale: The correct answer is A: Mouth. In the mouth, salivary amylase is secreted, which starts breaking down carbohydrates into simpler sugars like maltose. This initial breakdown of carbohydrates through the enzyme amylase marks the beginning of chemical digestion. The stomach primarily digests proteins, not carbohydrates (eliminating option B). The small intestine is where most of the carbohydrate digestion and absorption occurs, but the process begins in the mouth (eliminating option C). The large intestine is responsible for absorbing water and electrolytes, not carbohydrate digestion (eliminating option D).