A major secretion of the esophagus is

Correct Answer: C

Rationale: The correct answer is C: mucus. The esophagus secretes mucus to facilitate the passage of food from the mouth to the stomach, providing lubrication and protection to the esophageal lining. Bile (A) is produced by the liver and stored in the gallbladder, amylase (B) is an enzyme produced by the pancreas to break down carbohydrates in the small intestine, and hydrochloric acid (D) is produced by the stomach to aid in digestion. None of these substances are major secretions of the esophagus.

Correct Answer: C

Rationale: The correct answer is C because cholecystokinin inhibits gastric secretions, stimulates pancreatic secretions high in enzymes, and stimulates contraction of the gall bladder and relaxation of the sphincter of Oddi. This hormone is released in response to the presence of fats and proteins in the small intestine, leading to the digestion and absorption of these nutrients. Choices A and B are incorrect as they do not fully capture the wide range of effects of cholecystokinin. Choice D is also incorrect because it includes the stimulation of bile secretion, which is not a direct effect of cholecystokinin.

Correct Answer: C

Rationale: The correct answer is C: brush border of the small intestine. Disaccharides are broken down into monosaccharides by specific enzymes located in the brush border of the small intestine. These enzymes include sucrase, lactase, and maltase. The breakdown of disaccharides into monosaccharides occurs in the final stage of carbohydrate digestion, allowing for absorption into the bloodstream. Choices A, B, and D are incorrect because disaccharides are not primarily digested in the stomach, the lumen of the small intestine, or the colon. The main site for disaccharide digestion is the brush border of the small intestine where these specific enzymes are located.

Correct Answer: A

Rationale: The correct answer is A because the absorption of glucose is indeed associated with sodium uptake. This process occurs through the sodium-glucose cotransporter located on the apical membrane of the enterocytes in the small intestine. Sodium acts as a co-transporter, helping to facilitate the absorption of glucose. This mechanism is crucial for efficient absorption of glucose in the GI tract. Choice B is incorrect as glucose is actually absorbed more rapidly than fructose due to differences in transport mechanisms. Choice C is incorrect since galactose and fructose are absorbed by different transporters at the brush border membrane. Choice D is also incorrect because the majority of water absorption occurs in the small intestine, not the colon.

Correct Answer: D

Rationale: Step 1: Reuptake of the transmitter at the presynaptic terminal: This process involves the retrieval of excess neurotransmitter molecules back into the presynaptic neuron, preventing excessive accumulation in the synapse. Step 2: Enzymatic degradation of the transmitter within the synapse: Enzymes break down excess neurotransmitter molecules in the synapse, helping to maintain optimal levels and preventing overstimulation of the post synaptic terminal. Step 3: Negative feedback to inhibit further release of the transmitter: When neurotransmitter levels are high, negative feedback mechanisms can inhibit further release, preventing excessive accumulation and maintaining synaptic balance. Summary: - Option A and B are correct because reuptake and enzymatic degradation help prevent excessive accumulation of neurotransmitters. - Option C is also correct as negative feedback mechanisms play a role in regulating neurotransmitter release. - Therefore, the correct answer is D, as all of the above mechanisms work together to prevent excessive accumulation of neurotransmitters.