Saliva does not normally contain:

Correct Answer: D

Rationale: The correct answer is D: Intrinsic factor. Saliva does not normally contain intrinsic factor, which is a protein produced by the stomach to aid in the absorption of vitamin B12. Saliva does contain isozymes, IgA antibodies, and lactoferrin. Isozymes are different forms of enzymes, IgA is an antibody important for immune defense, and lactoferrin is a protein with antimicrobial properties found in saliva. Therefore, D is the correct answer as intrinsic factor is not a normal component of saliva.

Correct Answer: C

Rationale: The correct answer is C because carcinoma of the esophagus often spreads locally, making complete removal difficult. This local spread can involve nearby structures, leading to a poor prognosis. Metastases to the liver or lung (choice A) typically occur later in the disease course, not before diagnosis. While some esophageal tumors may be challenging to access surgically (choice B), this alone does not explain the poor prognosis. Esophageal cancer can respond to radiotherapy (choice D), so radioresistance is not the primary reason for the poor prognosis. In summary, the local spread preventing complete removal is the key factor contributing to the poor prognosis in esophageal carcinoma.

Correct Answer: B

Rationale: The correct answer is B because the buccal phase of swallowing is a voluntary process where the tongue moves the bolus of food towards the back of the mouth to initiate swallowing. This phase is under conscious control and initiates the swallowing reflex. Choice A is incorrect because the buccal phase is voluntary, not involuntary. Choice C is incorrect because the bolus is moved towards the back of the mouth, not rolled over the front of the tongue. Choice D is incorrect because the movement of food from the pharynx to the esophagus occurs during the pharyngeal phase of swallowing, not the buccal phase.

Correct Answer: D

Rationale: The correct answer is D: Submucosa. The submucosa is the layer of tissue beneath the mucosa in the gastrointestinal tract. It contains blood vessels, nerves, and glands that support the mucosa. Muscularis externa (A) is the layer of smooth muscle responsible for peristalsis. Circular muscle (B) is a type of muscle fiber found within the muscularis externa. Serosa (C) is the outermost layer of the digestive tract that provides protection and secretes fluid. The submucosa (D) is the correct answer because it is the layer directly beneath the mucosa and plays a crucial role in supporting and nourishing the mucosal layer.

Correct Answer: B

Rationale: The correct answer is B: To increase surface area for absorption. Villi and microvilli are tiny finger-like projections in the small intestine that greatly increase the surface area for nutrient absorption. This increased surface area allows for more efficient absorption of nutrients into the bloodstream. Choice A is incorrect because villi and microvilli do not secrete digestive enzymes; rather, they facilitate absorption of nutrients already broken down by enzymes. Choice C is incorrect as villi and microvilli do not transport nutrients to the liver; they absorb nutrients into the bloodstream for circulation to various body tissues. Choice D is incorrect because villi and microvilli do not store excess nutrients; their primary function is absorption.