The mucosal cells of the human colon perform the following functions:

Correct Answer: C

Rationale: Rationale: 1. The mucosal cells of the colon absorb Na to maintain electrolyte balance. 2. Na absorption is crucial for water reabsorption. 3. This process helps regulate stool consistency and prevent dehydration. Summary: A: Incorrect - Bile acid conversion primarily occurs in the liver. B: Incorrect - Bilirubin breakdown mainly occurs in the liver and intestines. D: Incorrect - Aromatic amino acid absorption occurs mainly in the small intestine.

Correct Answer: A

Rationale: The correct answer is A because secretin hormone is released in response to acidic gastric juice, acting to neutralize the acidity by stimulating pancreatic bicarbonate secretion. Choice B and C are incorrect as secretin does not stimulate stomach mobility or HCL secretion. Therefore, the correct answer is A as it aligns with the function of secretin in regulating pH balance in the digestive system.

Correct Answer: D

Rationale: Correct Answer: D Rationale: 1. Chemotrypsinogen is the inactive precursor of chymotrypsin. 2. Trypsin activates chemotrypsinogen to form active chymotrypsin. 3. This activation occurs in the small intestine, enabling protein digestion. Summary: A: Trypsin is secreted as an inactive zymogen, not in the active form. B: CCK stimulates enzyme secretion, not bicarbonate. C: Secretin mainly stimulates bicarbonate secretion, not enzymes.

Correct Answer: D

Rationale: The correct answer is D: Colon. The colon has the longitudinal muscle of the muscularis arranged into distinct longitudinal bundles called taeniae coli. This unique structure helps in the formation of haustra, the pouches seen in the colon. In contrast, the duodenum, jejunum, and ileum do not have this specific arrangement of longitudinal muscle bundles. The duodenum has a smooth muscle layer, while the jejunum and ileum have a continuous layer of smooth muscle without distinct longitudinal bundles. Therefore, the colon is the region of the GI tract where the longitudinal muscle is organized into distinct bundles.

Correct Answer: D

Rationale: The correct answer is D: Lungs. The lungs are not a part of the digestive system. The digestive system is responsible for breaking down food into nutrients, absorbing those nutrients, and eliminating waste. The lungs are part of the respiratory system, responsible for gas exchange. Liver (A) and gallbladder (B) are both part of the digestive system, aiding in digestion and nutrient absorption. Absorption (C) is a process within the digestive system, not a separate entity. In summary, the lungs do not play a role in the digestion process, making them the correct answer choice.