The center of the tooth that is filled with blood vessels and nerves is called the ______ and the cavity within the root of the tooth is called the ______.

Correct Answer: B

Rationale: The correct answer is B: pulp cavity; root canal. The pulp cavity is the center of the tooth filled with blood vessels and nerves, while the root canal is the cavity within the root of the tooth. This is because the pulp cavity contains the pulp tissue, which includes blood vessels and nerves, providing nourishment and sensation to the tooth. The root canal, on the other hand, is the space within the root where the pulp tissue extends down into. Choices A, C, and D are incorrect because they do not accurately describe the specific structures mentioned in the question.

Correct Answer: A

Rationale: The correct answer is A: gastric pits. Gastric pits are invaginations in the stomach lining that contain specialized cells for secretion of gastric juices. These pits increase the surface area of the stomach by providing a larger area for nutrient absorption and digestion. Plicae circulares are folds in the small intestine, not the stomach. Villi and microvilli are found in the small intestine and further increase surface area for absorption, not in the stomach.

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.