Which one of the following parts of the GI tract has the following characteristics: simple columnar epithelium, muscularis mucosa, Meissner's plexus, two layers of smooth muscle in the tunica muscularis and Peyer's patches of lymph nodules?

Correct Answer: C

Rationale: Rationale: 1. Simple columnar epithelium: Lines the inner surface of the GI tract for absorption. 2. Muscularis mucosa: Thin layer of smooth muscle for mucosal movement. 3. Meissner's plexus: Submucosal nerve plexus for controlling secretions. 4. Two layers of smooth muscle in the tunica muscularis: Helps in peristalsis. 5. Peyer's patches of lymph nodules: Part of the immune system in the GI tract, mainly found in the ileum for protection against pathogens. Therefore, the correct answer is C: ileum, as it has all the mentioned characteristics. Summary: A: duodenum - Lacks Peyer's patches and two layers of smooth muscle. B: jejunum - Lacks Meissner's plexus and Peyer's patches. D: colon - Lacks simple columnar epithelium, Meissner's plexus

Correct Answer: C

Rationale: The correct answer is C: bile salts; lipase. Bile salts emulsify lipids by breaking them down into smaller droplets to increase the surface area for digestion by lipase. Lipase is the enzyme responsible for digesting lipids into fatty acids and glycerol. Option A is incorrect because lipase digests lipids, not bile salts. Option B is incorrect because amylase digests carbohydrates, not lipids. Option D is incorrect because pepsin is an enzyme that digests proteins, not lipids.

Correct Answer: A

Rationale: The correct answer is A because mucous cells in the stomach lining secrete the glycoprotein mucin, which helps protect the stomach lining from the acidic environment and digestive enzymes. This is crucial for maintaining the integrity of the stomach wall and preventing damage. Chief cells (option B) secrete pepsinogen, not gastrin. Parietal cells (option C) secrete hydrochloric acid and intrinsic factor, not pepsinogen. G cells (option D) secrete gastrin, a hormone that stimulates acid secretion but do not secrete hydrochloric acid directly. Therefore, option A is correct as it accurately describes the function of mucous cells in the stomach lining.

Correct Answer: B

Rationale: The correct answer is B because during the teen years, the brain undergoes significant changes in neural connections. New connections are formed through processes like synaptic pruning, which strengthens important connections and eliminates unnecessary ones. This dynamic phase is crucial for learning and adapting to new experiences. Choices A, C, and D are incorrect because neural networks in the brain are not static and unchanging. The brain continues to reorganize and adapt throughout life, with myelination increasing to improve signal transmission efficiency, not decreasing as in choice D. Choice C is also incorrect as brain size does not significantly increase during the teen years, but rather the focus is on optimizing existing neural connections.

Correct Answer: D

Rationale: The correct answer is D because mitochondria are the main source of reactive oxygen species (ROS), which can damage DNA. Mitochondrial DNA is located near the electron transport chain where ROS are produced. This proximity increases the chances of oxidative damage to the mitochondrial DNA. Choices A, B, and C are incorrect because mitochondrial DNA polymerase does have some proof-reading activity, oxygen content is necessary for mitochondrial function, and mitochondrial DNA damage is not solely due to aging but also due to ROS production.