Mechanical digestion begins in the:

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.

Correct Answer: D

Rationale: The correct answer is D because esomeprazole (Nexium) is a proton pump inhibitor that works by decreasing stomach acid production, thereby treating gastroesophageal reflux disease. This explanation is important for the patient to understand the mechanism of action of the medication. Choice A is incorrect because esomeprazole does not increase the rate of gastric emptying; instead, it reduces acid production. Choice B is incorrect because esomeprazole does not neutralize stomach acid immediately; it takes a few days to reach its full effect. Choice C is incorrect because esomeprazole does not coat and protect the stomach and esophagus; it works by reducing acid production. In summary, the correct answer is D because it accurately describes how esomeprazole works to manage recurring heartburn by decreasing stomach acid production, which is essential for treating gastroesophageal reflux disease.

Correct Answer: B

Rationale: The correct answer is B: pyloric valve. The pyloric valve is located between the stomach and the small intestine, specifically at the junction of the stomach and the duodenum. Its main function is to regulate the flow of partially digested food from the stomach into the small intestine. This control is crucial to ensure that the small intestine receives food at a manageable rate for optimal digestion and absorption of nutrients. The cardiac sphincter (A) is located at the entrance of the stomach from the esophagus and prevents acid reflux. The ileo-colic valve (C) is located between the small and large intestines, controlling the flow of contents between them. The sphincter of Oddi (D) regulates the flow of bile and pancreatic juice into the small intestine.

Correct Answer: B

Rationale: The falciform ligament separates the right and left lobes of the liver. This is because it attaches the liver to the anterior abdominal wall and suspends it from the diaphragm, dividing the liver into right and left lobes. The quadrate, caudate, and pancreatic lobes are not separated by the falciform ligament, making choices A, C, and D incorrect, respectively.

Correct Answer: C

Rationale: The correct answer is C: jejunum. The jejunum is the middle part of the small intestine where the majority of nutrient absorption takes place. Its large surface area, due to the presence of villi and microvilli, facilitates efficient absorption of nutrients. The duodenum (B) primarily aids in digestion, not absorption. The ileum (D) absorbs bile salts and vitamin B12, but most nutrient absorption occurs in the jejunum. The colon (A) primarily absorbs water and electrolytes, not nutrients. Therefore, the jejunum is the correct answer for the site of most nutrient absorption in the digestive system.