In the small intestine, movement of chyme is regulated primarily by

Correct Answer: C

Rationale: The correct answer is C: local and mechanical stimulation. In the small intestine, movement of chyme is primarily regulated by local and mechanical stimulation, which triggers peristalsis and segmentation. This allows for the mixing and propulsion of chyme along the digestive tract. A: Secretin and cholecystokinin are hormones involved in regulating pancreatic and gallbladder secretions, not movement of chyme in the small intestine. B: The parasympathetic nervous system via the vagus nerve plays a role in stimulating digestive processes but is not the primary regulator of movement of chyme. D: The enterogastric reflex is related to regulating stomach emptying in response to irritating substances, not movement of chyme in the small intestine.

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.

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.