The tunica muscularis in the superior esophagus is made up of ______ muscle.

Correct Answer: A

Rationale: The correct answer is A: skeletal muscle. The superior esophagus contains skeletal muscle in its tunica muscularis, allowing for voluntary control over swallowing. Cardiac muscle is found in the heart, not in the esophagus. Smooth muscle is present in the lower esophagus for involuntary movements. Choice D is incorrect as the superior esophagus does not contain a mix of smooth and skeletal 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: D

Rationale: The correct answer is D because the described sequence of events matches the process of swallowing. Raising the larynx and hyoid bone helps to protect the airway, closing the epiglottis prevents food from entering the trachea, closing the soft palate blocks the nasopharynx to prevent food from entering the nasal cavity, and the contraction of the diaphragm and abdominal muscles along with relaxation of the lower esophageal sphincter facilitate the movement of food into the esophagus. This series of actions is characteristic of the swallowing reflex. Choices A, B, and C are incorrect. Low blood glucose levels do not directly trigger the swallowing reflex. Irritation in the GI tract would not lead to the described sequence of events. Bolus entering the larynx or nasopharynx would not be part of the normal swallowing process and would typically trigger the gagging reflex instead.

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.