In which of the following regions of the GI tract does the mucosa most closely resemble that of the colon, but with more lymphoid tissue?

Correct Answer: D

Rationale: The correct answer is D: appendix. The mucosa of the appendix closely resembles that of the colon but with more lymphoid tissue due to its role in the immune system. The appendix contains a high concentration of lymphoid tissue which helps in the immune response. The stomach (A) has gastric pits and glands for digestion, the duodenum (B) is involved in nutrient absorption, and the jejunum (C) is primarily responsible for nutrient absorption. Therefore, the appendix is the correct answer as it matches the description provided in the question.

Correct Answer: D

Rationale: The correct answer is D: 1-2 microns. Microvilli are small, finger-like projections on the surface of cells that increase surface area for absorption. They are generally 1-2 microns in length. A is incorrect as 10-20 millimeters would be too long for microvilli. B is incorrect as 0.5-1.0 millimeters is also too long. C is incorrect as 20-50 microns is within the range of the length of cilia, not microvilli. Therefore, the correct answer is D based on the typical length of microvilli.

Correct Answer: B

Rationale: The correct answer is B: chief (zymogenic) cells. These cells are responsible for secreting pepsinogen, which is the inactive form of pepsin, an enzyme that helps in the digestion of proteins in the stomach. Goblet cells (A) secrete mucus, parietal (oxyntic) cells (C) secrete hydrochloric acid, and Kupffer cells (D) are found in the liver and are involved in immune function, not in stomach digestion. Therefore, the correct choice is chief (zymogenic) cells as they specifically secrete pepsinogen for protein digestion in the stomach.

Correct Answer: D

Rationale: The correct answer is D because cells lining the sides of intestinal crypts of Lieberkühn are responsible for supplying replacement cells for the epithelium of villi. These cells undergo rapid division and differentiation to replace the cells shed from the villi, ensuring the continuous renewal and maintenance of the intestinal lining. This process is crucial for the absorption of nutrients and maintaining the integrity of the intestinal barrier. Choice A (secreting digestive enzyme) is incorrect because the cells in the intestinal crypts primarily function in cell replacement, not enzyme secretion. Choice B (secreting one of several various hormones) is incorrect as the main function of these cells is not hormone secretion but rather cell turnover. Choice C (secreting mucus) is incorrect as mucus secretion is typically associated with other specialized cells in the intestinal lining, such as goblet cells, not the cells in the crypts responsible for cell replacement.

Correct Answer: D

Rationale: Absorptive epithelial cells of the small intestine (enterocytes) are characterized by: A: Apical brush border composed of microvilli - This increases surface area for absorption. B: A glycocalyx containing various digestive enzymes - This aids in digestion and absorption. C: Junctional complexes including tight junctions separating apical from lateral cell membranes - This maintains cell polarity and regulates permeability. Therefore, choice D is correct as all these characteristics are typical of absorptive epithelial cells in the small intestine.