The most common cause of tooth loss in adults is

Correct Answer: A

Rationale: The correct answer is A: periodontal disease. Periodontal disease is the most common cause of tooth loss in adults due to the severe damage it causes to the supporting structures of the teeth, such as the gums and bone. It leads to progressive destruction of the tissues surrounding the teeth, eventually resulting in tooth loss. Gingivitis (B) and pyorrhea (C) are stages of periodontal disease and not the primary cause of tooth loss. Dental caries (D) primarily affects the enamel and dentin of the teeth, leading to cavities, but it is not as common a cause of tooth loss in adults as periodontal disease.

Correct Answer: C

Rationale: The correct answer is C: duodenum. The pancreas and liver release their secretions, such as pancreatic enzymes and bile, into the duodenum. This is because the duodenum is the first part of the small intestine where digestion primarily occurs. The stomach (A) is responsible for initial digestion of food, while the ileum (B) and jejunum (D) are parts of the small intestine where absorption of nutrients occurs, not secretion release.

Correct Answer: D

Rationale: The correct answer is D: enterokinase; small intestine. Enterokinase is an enzyme that activates trypsinogen into trypsin in the small intestine. Trypsin is then responsible for breaking down proteins in the small intestine. Enterokinase is not found in the pancreatic ducts, eliminating choices A and C. Trypsinogen is not activated by itself, so choice B is incorrect. In summary, enterokinase activates trypsinogen into trypsin in the small intestine, allowing for protein digestion.

Correct Answer: B

Rationale: The correct answer is B: lacteals. Chylomicrons are too large to enter capillaries directly, so they are absorbed into lacteals, specialized lymphatic vessels in the small intestine. Lacteals transport chylomicrons to the lymphatic system, eventually reaching the bloodstream via the thoracic duct. Arterioles and venules are part of the blood circulation system and are not directly involved in chylomicron absorption.

Correct Answer: D

Rationale: The correct answer is D because butyric acid, a short-chain fatty acid formed during colonic fiber fermentation, has been shown to stimulate antioxidant defenses in the colon. This helps protect against oxidative damage, a key factor in the development of cancer. Choice A is incorrect because propionic acid does not inhibit liver fatty acid synthesis in relation to colon cancer. Choice B is incorrect because butyric acid does not silence the SLC5A8 tumor suppressor gene; in fact, it has been shown to have anti-tumor effects. Choice C is incorrect as there is evidence supporting the protective effect of dietary fiber through butyric acid's stimulation of antioxidant defenses.