Which is not a feature of digestive motility?

Correct Answer: A

Rationale: The correct answer is A. Peristalsis involves coordinated waves of muscle contractions that propel food forward. However, peristalsis can also involve backward movements to help with mixing and digestion. Therefore, the statement that peristalsis only involves forward movements is incorrect. Segmentation involves mixing and breaking down food through contractions that occur in non-unidirectional patterns. Peristalsis can be found in the esophagus, stomach, and intestines, while segmentation is mainly present in the small intestine. Therefore, choices B, C, and D are incorrect based on the explanations provided.

Correct Answer: B

Rationale: The correct answer is B: Sodium-glucose co-transport system. This system involves the active transport of glucose across the small intestine epithelial cells with the help of sodium ions. This mechanism allows for the absorption of glucose against its concentration gradient, ensuring efficient uptake. Other choices are incorrect because: A) Simple passive diffusion is not efficient for glucose absorption due to its hydrophilic nature. C) Osmosis is the movement of water molecules, not glucose. D) Primary active transport involves the direct use of energy to transport molecules, which is not the case for glucose absorption in the small intestine.

Correct Answer: B

Rationale: Step-by-step rationale: 1. Gastric secretions contain intrinsic factor, essential for vitamin B12 absorption from the terminal ileum. 2. Intrinsic factor binds to vitamin B12 to facilitate its absorption. 3. Without intrinsic factor, vitamin B12 absorption is impaired, leading to pernicious anemia. 4. Therefore, choice B is correct. Summary: - Choice A is incorrect as gastric secretions increase, not decrease, when a person thinks of food. - Choice C is incorrect as hydrochloric acid (HCl) is secreted by parietal cells, not chief cells. - Choice D is incorrect as fat digestion primarily occurs in the small intestine with the help of pancreatic enzymes, not gastric secretions.

Correct Answer: A

Rationale: The correct answer is A: Amylase. Amylase is an enzyme that specifically breaks down carbohydrates into sugars in the mouth. It is produced by both salivary glands and pancreas. Protease (B) breaks down proteins, Lipase (C) breaks down fats, and Pepsin (D) breaks down proteins in the stomach. Therefore, A is the correct answer for the enzyme responsible for breaking down carbohydrates in the mouth.

Correct Answer: A

Rationale: The correct answer is A: mouth. Mechanical digestion begins in the mouth where food is chewed and mixed with saliva, breaking down into smaller pieces for easier swallowing and digestion. This process increases the surface area of food for enzymes to act upon. The stomach (B) primarily performs chemical digestion, the small intestine (C) is where most chemical digestion and absorption occur, and the large intestine (D) is mainly responsible for water absorption and formation of feces. Thus, the mouth is the correct choice for the beginning of mechanical digestion.