Which of the following mechanisms most accurately describes how pseudo-membranous colitis caused by Clostridium difficile is produced?

Correct Answer: A

Rationale: The correct answer is A because Clostridium difficile produces toxins, specifically enterotoxins, which cause damage to the intestinal mucosa leading to pseudo-membranous colitis. The organism colonizes the colon and then elaborates the toxins, which disrupt the mucosal barrier. Choice B is incorrect as there is no preformed toxin ingested; the toxin is produced by the organism after colonization. Choice C is incorrect as Clostridium difficile does not invade and destroy the mucosa directly. Choice D is incorrect as the host immune response is a consequence of the toxin production, not the primary mechanism of disease.

Correct Answer: C

Rationale: The correct answer is C: Bile salts are produced by the liver from cholesterol. Rationale: 1. Bile salts aid in the emulsification and digestion of fats, not proteins (A). 2. Pancreatic amylase is responsible for carbohydrate digestion, not bile salts (B). 3. The liver synthesizes bile salts from cholesterol to facilitate fat digestion and absorption (C). 4. Bile salts reduce lipid surface tension to form micelles, aiding in fat digestion, rather than increasing it (D).

Correct Answer: A

Rationale: The correct answer is A because salivary secretion contains enzymes like amylase that start the digestion of carbohydrates in the mouth. This enzyme breaks down complex carbohydrates into simpler sugars. Choices B, C, and D are incorrect because salivary secretion is not directly controlled by secretin hormone, does not start the digestion of proteins, and is not highly acidic. Salivary secretion primarily aids in the initial breakdown of carbohydrates, preparing them for further digestion in the stomach and intestines.

Correct Answer: C

Rationale: The correct answer is C because Cholecystokinin (CCK) is a hormone secreted by the duodenum in response to the presence of fats and proteins. It stimulates the pancreatic acini to secrete digestive enzymes such as lipase and proteases. This helps in the digestion and absorption of fats and proteins. The other choices are incorrect because A is false - CCK is secreted by the duodenum, not the gastric antrum. B is false - CCK is actually stimulated by the presence of fats in the duodenum. D is false - CCK actually stimulates gallbladder contraction to release bile, aiding in fat digestion.

Correct Answer: C

Rationale: The correct answer is C: Mucosa and Lumen. The mucosa surface cell secretes mucus that forms a physical barrier between the mucosa (inner lining of a cavity or organ) and the lumen (inner space of a tubular structure). This barrier protects the underlying tissues from harmful substances in the lumen. Choice A (Mucosa and Epithelium) is incorrect because the mucosa is part of the epithelium layer, so it would not make sense for the physical barrier to be between them. Choice B (Lymph Vessel and Lamina Propria) is incorrect because these structures are not directly related to the secretion of mucus for protection. Choice D (Lumen and Epithelium) is incorrect because the physical barrier created by the mucus is specifically between the mucosa cells and the lumen, not the epithelium itself.