The lymphatic capillaries in the villi of the small intestine are called

Correct Answer: A

Rationale: The correct answer is A: lacteals. Lacteals are specialized lymphatic capillaries found in the villi of the small intestine that absorb dietary fats and fat-soluble vitamins. They play a crucial role in the transport of these nutrients to the bloodstream. Peyer's patches (B) are lymphoid nodules in the small intestine involved in immune responses. Crypts of Lieberkuhn (C) are intestinal glands that secrete digestive enzymes. Microvilli (D) are small projections on the surface of intestinal cells that increase surface area for nutrient absorption but are not lymphatic capillaries.

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: B

Rationale: The correct answer is B because the teniae coli are bands of longitudinal smooth muscle in the colon. These bands contract to form haustra, which are the pouches that give the colon its segmented appearance. Choice A is incorrect because fat and epiploic appendages are not involved in the contraction of the colon. Choice C is incorrect because the teniae coli are smooth muscle, not skeletal muscle. Choice D is incorrect because the internal anal sphincter is not formed by the contraction of the teniae coli.

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.