The pharyngeal phase of swallowing is ______ , which is controlled by ______ muscle.

Correct Answer: C

Rationale: The pharyngeal phase of swallowing is an involuntary process, meaning it occurs automatically without conscious control. This phase involves the contraction of skeletal muscles in the pharynx to propel the food bolus towards the esophagus. Skeletal muscles are under voluntary control, but in the context of swallowing, the pharyngeal phase is involuntary. Thus, the correct answer is C: involuntary; skeletal. Choice A (involuntary; smooth) is incorrect because smooth muscles are not typically involved in the pharyngeal phase of swallowing. Choice B (voluntary; smooth) is incorrect because the pharyngeal phase is not under voluntary control, and smooth muscles are not the primary muscles involved. Choice D (voluntary; skeletal) is incorrect because the pharyngeal phase is involuntary and skeletal muscles, not smooth muscles, are responsible for the muscle contractions during this phase.

Correct Answer: B

Rationale: The gallbladder contracts in response to cholecystokinin and vagal stimulation. Cholecystokinin is released in response to the presence of fatty acids and amino acids in the duodenum, signaling the gallbladder to contract and release bile. Vagal stimulation also plays a role in gallbladder contraction by transmitting signals from the brain to the gallbladder. Secretin is primarily involved in stimulating pancreatic secretion, not gallbladder contraction. A low pH of chyme does not directly stimulate gallbladder contraction.

Correct Answer: D

Rationale: The correct answer is D because glucose and galactose are taken into the epithelial cell by cotransport, where they are coupled with sodium ions. This process maintains a concentration gradient for glucose and galactose to move against. Once inside the cell, they are passed into the interstitial fluid by facilitated diffusion, where transport proteins assist their movement down their concentration gradient. Choices A and B are incorrect because they do not involve active transport, which is necessary to move molecules against their concentration gradient. Choice C is incorrect because active transport requires energy input, whereas facilitated diffusion does not.

Correct Answer: D

Rationale: Correct Answer: D Rationale: Salivary amylase primarily digests carbohydrates in the oral cavity, breaking down starch into simpler sugars like maltose. It does not directly target the dextran film on tooth enamel formed from dietary sucrose. This film is typically broken down by dental plaque bacteria, not salivary amylase. Therefore, option D is incorrect. Summary of Incorrect Choices: A: This statement is correct. Chewing and swallowing do require energy expenditure. B: This statement is correct. Swallowing involves the coordinated action of multiple muscle groups. C: This statement is correct. The biofilm on tooth enamel contains enzymes from both saliva and bacteria, contributing to oral digestion.

Correct Answer: B

Rationale: The correct answer is B: Schwann cells and oligodendrocytes. Schwann cells produce myelin in the peripheral nervous system, while oligodendrocytes produce myelin in the central nervous system. Myelin insulates nerve axons, allowing for saltatory conduction, greatly increasing the speed of transmission. Nodes of Ranvier are gaps in the myelin sheath where action potentials are regenerated, not where myelin is produced. Neurons themselves do not produce myelin. Astrocytes and ependymal cells have supportive roles in the nervous system but do not produce myelin.