Which of these is the site of most chemical digestion?

Correct Answer: B

Rationale: The correct answer is B: small intestine. The majority of chemical digestion occurs in the small intestine, specifically in the duodenum, where enzymes from the pancreas and bile from the liver break down food into nutrients. Stomach primarily performs mechanical digestion and initial protein breakdown. Mouth initiates mechanical digestion through chewing and begins carbohydrate digestion. Large intestine mainly absorbs water and electrolytes. Therefore, small intestine is the site of most chemical digestion due to its specialized enzymes and processes.

Correct Answer: C

Rationale: The correct answer is C: Secreting digestive enzymes. The pancreas secretes digestive enzymes such as amylase, lipase, and proteases to break down carbohydrates, fats, and proteins in the small intestine. This aids in digestion and absorption of nutrients. Producing insulin (Choice A) is a function of the pancreas but is primarily related to regulating blood sugar levels, not digestion. Producing bile (Choice B) is a function of the liver, not the pancreas. Absorbing nutrients (Choice D) is a function of the small intestine, not the pancreas. Therefore, the correct answer is C based on the role of the pancreas in digestion and enzyme secretion.

Correct Answer: D

Rationale: The correct answer is D, bile salts. The jejunum is primarily responsible for the absorption of nutrients like glucose, amino acids, and fatty acids. Bile salts are mainly absorbed in the ileum, the part of the small intestine that follows the jejunum. Bile salts aid in the digestion and absorption of fats, but they are not absorbed in the jejunum. Therefore, the jejunum is not the main site for absorption of bile salts. This makes option D the correct answer.

Correct Answer: D

Rationale: The correct answer is D because the pharyngeal phase of swallowing involves the contraction of the pharyngeal constrictors, which propel the bolus of food or liquid down the pharynx towards the esophagus. This muscular contraction helps in the proper movement of the swallow. A, a deep breath, is not part of the pharyngeal phase but may precede swallowing. B, elevation of the tongue against the hard palate, is part of the oral phase of swallowing, not the pharyngeal phase. C, contraction of the upper esophageal sphincter, occurs in the esophageal phase, not the pharyngeal phase.

Correct Answer: D

Rationale: The correct answer is D: Bicarbonate ions. Acinar cells in the exocrine pancreas are responsible for secreting digestive enzymes, which are stimulated by secretin, CCK, and parasympathetic stimulation. Bicarbonate ions, on the other hand, are secreted by ductal cells in the pancreas to neutralize the acidic chyme entering the small intestine. Therefore, an increase in bicarbonate ions would not directly affect the secretion of acinar cells. Secretin stimulates the release of bicarbonate ions, while CCK and parasympathetic stimulation trigger the release of digestive enzymes. So, choice D is the correct answer because it does not directly increase the secretion of acinar cells within the exocrine pancreas.