Which part of the digestive system is responsible for the absorption of nutrients?

Correct Answer: A

Rationale: The correct answer is A, the small intestine, because it is the primary site for nutrient absorption in the digestive system. The small intestine is lined with villi and microvilli, increasing its surface area for efficient absorption. It contains specialized cells that transport nutrients into the bloodstream for distribution to the body. The stomach (B) primarily breaks down food using digestive enzymes and acids, while the pancreas (C) secretes digestive enzymes but does not directly absorb nutrients. The liver (D) plays a role in bile production and detoxification, but nutrient absorption occurs mainly in the small intestine.

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.

Correct Answer: C

Rationale: The correct answer is C: both. Occult fecal blood can indicate bleeding anywhere along the gastrointestinal tract. Upper gastrointestinal bleeding typically presents as melena (black, tarry stools), while lower gastrointestinal bleeding can manifest as occult blood in the stool. Therefore, occult fecal blood can be an indication of both upper and lower gastrointestinal bleeding. Choices A and B are incorrect because occult fecal blood is not exclusive to either upper or lower gastrointestinal bleeding alone. Choice D is incorrect since occult fecal blood can indeed be an indication of gastrointestinal bleeding.