Which of the following regions of the GI tract is characterized by permanent folds (plica)?

Correct Answer: C

Rationale: The correct answer is C: small intestine. The small intestine is characterized by permanent folds called plicae circulares, which increase the surface area for nutrient absorption. These folds help to slow down the passage of food and increase contact with the intestinal walls. The other choices are incorrect because the esophagus (A) does not have permanent folds, the stomach (B) has rugae (temporary folds), and the large intestine (D) has haustra (pouches), not permanent folds like the small intestine.

Correct Answer: A

Rationale: The correct answer is A. The thickness of the stomach wall (all layers) is about 1-2 millimeters. This includes the mucosa, submucosa, muscularis, and serosa layers, which together make up the entire thickness of the stomach wall. The other choices are incorrect because: B. The thickness of the gastric mucosa is much thinner than 1-2 millimeters. C. The height of the stomach's surface epithelial cells is a microscopic measurement, not in the millimeter range. D. The diameter of a parietal cell is also a microscopic measurement, not in the millimeter range. Therefore, the correct answer is A based on the actual dimensions of the structures mentioned in the question.

Correct Answer: D

Rationale: The correct answer is D because epithelial cells lining striated intralobular ducts are usually simple cuboidal or columnar cells (A), have eosinophilic cytoplasm containing numerous mitochondria for energy production (B), and have basal cell membranes extensively folded to increase the surface area for active ion pump molecules (C). Choice A describes the cell morphology, choice B relates to cytoplasm content, and choice C pertains to membrane structure, all of which are characteristics of these cells. Therefore, selecting all three choices (D) accurately describes the features of epithelial cells in striated intralobular ducts.

Correct Answer: D

Rationale: The correct answer is D: absorbing nutrients. Enterocytes in the small intestine are primarily responsible for absorbing nutrients from digested food. They have specialized structures like microvilli to increase surface area for absorption. Choice A is incorrect because enterocytes do not secrete digestive enzymes; that is done by other cells in the small intestine. Choice B is incorrect because hormone secretion is mainly done by endocrine cells in the intestine. Choice C is incorrect because goblet cells are responsible for secreting mucus in the intestine, not enterocytes. In summary, enterocytes' main function is to absorb nutrients, not secrete enzymes, hormones, or mucus.

Correct Answer: D

Rationale: The correct answer is D: adipocyte. Adipocytes are not typical of lamina propria, which is a loose connective tissue found in mucous membranes. Adipocytes are fat cells, primarily found in adipose tissue, not in the lamina propria. Lymphocytes (A), fibroblasts (B), and macrophages (C) are all commonly found in the lamina propria. Lymphocytes are involved in the immune response, fibroblasts produce collagen and extracellular matrix, and macrophages are phagocytic cells that help in defense and tissue repair. In summary, adipocytes do not belong in the lamina propria as they are not typical connective tissue cells found in this specific tissue layer.