The salivary gland that produces primarily mucus is the ______ salivary gland.

Correct Answer: D

Rationale: The correct answer is D: sublingual gland. This gland primarily produces mucus, aiding in lubrication and initial digestion. The sublingual gland is located under the tongue. A: The parotid gland primarily produces serous saliva. B: Labial glands are minor salivary glands located in the lips, producing mixed saliva. C: Submandibular gland produces a mixture of serous and mucous saliva.

Correct Answer: B

Rationale: The correct answer is B because the low pH of the stomach activates pepsin, an enzyme that digests proteins, while inactivating salivary amylase, an enzyme that digests starch. Pepsin works optimally in an acidic environment, breaking down proteins into peptides. Salivary amylase, on the other hand, works best at a neutral pH and is denatured in the acidic stomach, leading to its inactivation. Choices A, C, and D are incorrect because lipids are primarily digested in the small intestine, and nucleic acids are not directly affected by the stomach's pH.

Correct Answer: A

Rationale: The correct answer is A: lacteals. Lacteals are specialized lymphatic capillaries found in the villi of the small intestine that absorb dietary fats and fat-soluble vitamins. They play a crucial role in the transport of these nutrients to the bloodstream. Peyer's patches (B) are lymphoid nodules in the small intestine involved in immune responses. Crypts of Lieberkuhn (C) are intestinal glands that secrete digestive enzymes. Microvilli (D) are small projections on the surface of intestinal cells that increase surface area for nutrient absorption but are not lymphatic capillaries.

Correct Answer: C

Rationale: The correct answer is C: local and mechanical stimulation. In the small intestine, movement of chyme is primarily regulated by local and mechanical stimulation, which triggers peristalsis and segmentation. This allows for the mixing and propulsion of chyme along the digestive tract. A: Secretin and cholecystokinin are hormones involved in regulating pancreatic and gallbladder secretions, not movement of chyme in the small intestine. B: The parasympathetic nervous system via the vagus nerve plays a role in stimulating digestive processes but is not the primary regulator of movement of chyme. D: The enterogastric reflex is related to regulating stomach emptying in response to irritating substances, not movement of chyme in the small intestine.

Correct Answer: A

Rationale: The correct answer is A because in the production of pancreatic juice, bicarbonate ions are actively transported into the intercalated duct to ensure the alkalinity of the pancreatic juice. Additionally, sodium ions are exchanged for hydrogen ions to maintain the pH balance. This process helps neutralize the acidic chyme entering the small intestine from the stomach. The other choices are incorrect because potassium ions are not directly involved in this specific process, and the exchange of sodium ions for potassium ions does not contribute to the regulation of pancreatic juice pH.