Contraction of the __________ layer of the intestinal wall functions to change the shape of the intestinal lumen and moves food through its length.

Correct Answer: D

Rationale: The correct answer is D: muscularis. The muscularis layer of the intestinal wall is responsible for peristalsis, the wave-like contractions that propel food through the digestive tract. The mucosa (A) is the innermost layer involved in absorption, not movement. The submucosa (B) provides support and nourishment to the mucosa. The adventitia (C) refers to connective tissue that surrounds organs, not directly involved in movement. Therefore, the muscularis (D) is the only layer specifically responsible for changing the shape of the intestinal lumen and moving food along its length.

Correct Answer: D

Rationale: The correct answer is D because Plicae Circularis and intestinal villi increase the surface area of the small intestine mucosa, aiding in absorption. Plicae Circularis are circular folds in the mucosa, while intestinal villi are finger-like projections. This increased surface area allows for more efficient absorption of nutrients. A: Incorrect. Plicae Circularis and intestinal villi do not produce new cells for the mucosa. B: Incorrect. These structures do not carry products of digestion that won't pass through blood capillaries. C: Incorrect. They do not produce hormones to aid in digestion. In summary, choice D is correct as Plicae Circularis and intestinal villi primarily function to increase the surface area of the small intestine mucosa, aiding in absorption of nutrients.

Correct Answer: D

Rationale: Step 1: The cephalic phase occurs before food enters the stomach, triggered by the sight, smell, or thought of food. Step 2: The vagus nerve sends signals to the stomach to prepare for food digestion during this phase. Step 3: Increased flow of action potentials along the vagus nerve stimulates gastric glands to secrete gastric juice. Step 4: Therefore, choice D is correct as it accurately describes the physiological response during the cephalic phase. Summary: Choices A and B are incorrect as they do not align with the physiological processes during the cephalic phase. Choice C is incorrect because distention of the stomach triggers the gastric phase, not the cephalic phase.

Correct Answer: C

Rationale: The correct answer is C: stomach. The stomach has 3 layers of smooth muscle in its muscularis externa, which help in mixing and churning food for digestion. The small intestine (A) has 2 layers of smooth muscle, the esophagus (B) has skeletal and smooth muscle, and the large intestine (D) has outer longitudinal and inner circular layers of smooth muscle, not 3 distinct layers like the stomach.

Correct Answer: C

Rationale: The correct answer is C because most ingested food molecules are large and need to be broken down into smaller molecules for absorption. Digestion involves the breakdown of complex nutrients into simpler forms that can be absorbed by the body. Choice A is incorrect because digestive enzymes can work on a variety of substrates, not necessarily requiring a variety. Choice B is incorrect as digestion is not primarily aimed at balancing the diet but rather extracting nutrients. Choice D is incorrect as digestion primarily occurs in the stomach and small intestine, not specifically to prevent disorders of the intestine.