In which part of the alimentary canal does most digestion occur?

Correct Answer: B

Rationale: The correct answer is B: proximal small intestine. Most digestion occurs in the proximal small intestine due to the presence of enzymes such as amylase, lipase, and protease, which break down carbohydrates, fats, and proteins, respectively. Additionally, bile and pancreatic juices are released in this part of the intestine to aid in digestion. The stomach primarily initiates digestion by breaking down food with stomach acid and enzymes, but the majority of nutrient absorption occurs in the small intestine. Choices A, C, and D are incorrect as the stomach is not the main site of digestion, the distal small intestine is more focused on absorption rather than digestion, and the ascending colon is primarily responsible for water absorption and formation of feces.

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: cuspids. Cuspids, also known as canines, are pointed teeth that are specifically adapted for tearing and shredding food. They have long, sharp points that help in grasping and cutting food. Incisors (A) are flat-front teeth used for cutting and biting. Bicuspids (B) are premolars with two cusps used for grinding food. Molars (C) are large, flat teeth at the back of the mouth used for grinding and chewing. Therefore, D is the correct answer as cuspids are the pointed teeth adapted for tearing and shredding.

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.