Where does the majority of carbohydrate digestion occur?

Correct Answer: C

Rationale: The majority of carbohydrate digestion occurs in the mouth. This is because the enzyme amylase, present in saliva, begins breaking down carbohydrates into simpler sugars like maltose. The process starts in the mouth as the food is chewed and mixed with saliva, creating a bolus that can be easily swallowed. In the stomach, the acidic environment actually inhibits amylase activity, so minimal carbohydrate digestion occurs there. The small intestine is where further digestion and absorption of carbohydrates primarily happen, but the initial breakdown in the mouth is crucial. The esophagus is not involved in digestion, but rather in the transportation of food to the stomach.

Correct Answer: B

Rationale: The correct answer is B: Chemical digestion of proteins. The stomach produces hydrochloric acid and enzymes like pepsin to break down proteins into peptides and amino acids. This process is essential for protein digestion. Mechanical digestion (A) occurs mainly in the mouth and intestines. Absorption of nutrients (C) primarily takes place in the small intestine. Neutralization of stomach acid (D) is not the primary role of the stomach; rather, the stomach maintains an acidic environment for digestion.

Correct Answer: C

Rationale: The correct answer is C because the pharyngeal phase of swallowing involves the peristaltic activity of the upper third of the esophagus, pushing the food bolus towards the stomach. This phase is involuntary and is controlled by the swallowing reflex. Choices A, B, and D are incorrect because the pharyngeal phase is entirely involuntary, the upper esophageal sphincter opens during the esophageal phase, and the opening of the glottis is associated with protection of the airway during swallowing, not the pharyngeal phase.

Correct Answer: D

Rationale: The correct answer is D: Absorption of sodium. Colonic mucosal cells are efficient in absorbing sodium through active transport processes. Sodium absorption helps in maintaining fluid and electrolyte balance. Choices A, B, and C are incorrect because primary bile acids are converted into secondary bile acids in the liver, bilirubin is converted into stercobilinogen in the intestines, and aromatic amino acids are mostly absorbed in the small intestine, not the colon.

Correct Answer: B

Rationale: The migrating motor complex (MMC) functions to clear non-digestible material from the stomach and small intestine during fasting periods. Step 1: During fasting, MMC promotes gastrointestinal motility to prevent bacterial overgrowth. Step 2: MMC consists of 3 phases - quiescent, irregular contractions, and intense contractions - aiding in sweeping undigested materials. Step 3: This process helps maintain gut health and prevents issues like bacterial overgrowth or malabsorption. Summary: Choices A, C, and D are incorrect as they do not accurately describe the specific function of the migrating motor complex during fasting.