In the production of the aqueous component of pancreatic juice, ______ ions are actively transported into the intercalated duct and sodium ions are exchanged for ______ ions.

Correct Answer: A

Rationale: The correct answer is A because in the production of pancreatic juice, bicarbonate ions are actively transported into the intercalated duct to ensure the alkalinity of the pancreatic juice. Additionally, sodium ions are exchanged for hydrogen ions to maintain the pH balance. This process helps neutralize the acidic chyme entering the small intestine from the stomach. The other choices are incorrect because potassium ions are not directly involved in this specific process, and the exchange of sodium ions for potassium ions does not contribute to the regulation of pancreatic juice pH.

Correct Answer: C

Rationale: The correct answer is C: low-density lipoprotein (LDL). LDL is often referred to as "bad cholesterol" because it carries cholesterol from the liver to the cells, leading to the buildup of plaque in the arteries, which can result in coronary heart disease. Micelles are small lipid structures, not carriers of cholesterol. Chylomicrons are large lipoprotein particles that transport dietary fats, not primarily cholesterol. HDL is known as "good cholesterol" as it helps remove cholesterol from the bloodstream back to the liver for excretion, reducing the risk of atherosclerosis.

Correct Answer: C

Rationale: The correct answer is C: Vitamin D. Vitamin D plays a crucial role in enhancing the absorption of calcium in the small intestine by promoting the synthesis of calcium-binding proteins. This process ensures adequate levels of calcium are absorbed efficiently. In contrast, choice A (sodium) does not directly impact calcium absorption, choice B (intrinsic factor) is involved in the absorption of vitamin B12, not calcium, and choice D (Vitamin K) is essential for blood clotting but not directly related to calcium absorption. Therefore, Vitamin D is the correct choice as it directly influences the active absorption of calcium in the small intestine.

Correct Answer: C

Rationale: The correct answer is C: Amylase. Amylase is primarily responsible for digesting carbohydrates in the small intestine. It breaks down complex carbohydrates into simpler sugars like maltose and glucose. Pepsin (A) is a stomach enzyme that breaks down proteins, not carbohydrates. Lipase (B) digests fats, not carbohydrates. Trypsin (D) is a pancreatic enzyme that digests proteins, not carbohydrates. Amylase is the only enzyme among the choices that specifically targets carbohydrates for digestion in the small intestine.

Correct Answer: C

Rationale: The correct answer is C: H+. Peptide transporter 1 requires a proton gradient for the active transport of di- and tripeptides across the enterocytes. This proton gradient is maintained by the H+ ions. Na+ (Choice A), Ca++ (Choice B), and Cl- (Choice D) are not directly involved in the transport of di- and tripeptides by peptide transporter 1. Na+ is primarily involved in glucose and amino acid transport, Ca++ in bone formation and muscle contraction, and Cl- in maintaining osmotic balance. Therefore, the correct answer is H+ as it is crucial for the functioning of peptide transporter 1.