Which of these substances is absorbed through the walls of the small intestine?

Correct Answer: D

Rationale: The correct answer is D: all of the above. The small intestine is where the majority of nutrient absorption occurs. Water is absorbed through osmosis, proteins are broken down into amino acids and absorbed through active transport, and lipids are broken down into fatty acids and absorbed through simple diffusion. Therefore, all three substances (water, proteins, and lipids) are absorbed through the walls of the small intestine. Choices A, B, and C are incorrect because each of these substances is indeed absorbed in the small intestine through different mechanisms.

Correct Answer: C

Rationale: The correct answer is C: small intestine. Fats are primarily digested in the small intestine. First, bile from the liver emulsifies fats, breaking them down into smaller droplets. Then, pancreatic enzymes like lipase break down these smaller droplets into fatty acids and glycerol for absorption. The small intestine is where the majority of nutrient absorption occurs, making it the main site for fat digestion. Explanation of why other choices are incorrect: A: Stomach - Minimal fat digestion occurs in the stomach as it primarily focuses on protein digestion. B: Pancreas - The pancreas secretes enzymes that aid in fat digestion, but the actual breakdown of fats happens in the small intestine. D: Large intestine - Fat digestion is not a primary function of the large intestine; it mainly absorbs water and electrolytes.

Correct Answer: D

Rationale: The correct answer is D: Control centers in the medulla oblongata. The myenteric plexus is a network of neurons located in the gastrointestinal tract, regulating gut motility independently. The myenteric plexus consists of sensory neurons, interneurons, and motor neurons. Control centers in the medulla oblongata are part of the central nervous system and are not directly involved in the myenteric plexus's functions. Therefore, they are not considered as component parts of the myenteric plexus.

Correct Answer: B

Rationale: The correct answer is B: Total gastrectomy. This operation involves complete removal of the stomach, leading to the inability to digest food. Without a stomach, essential nutrients cannot be absorbed, necessitating parenteral feeding. A: Total oesophagectomy - Although the esophagus is important for swallowing, parenteral feeding can sustain life without it. C: Right hepatic lobectomy - The liver has regenerative capacity and can compensate for the loss of a lobe. D: Total oroclocolectomy - This operation removes the entire colon, but parenteral feeding can still provide nutrition. In summary, total gastrectomy results in the loss of the major organ responsible for digestion and nutrient absorption, requiring parenteral feeding for survival.

Correct Answer: D

Rationale: The correct answer is D: Intrinsic factor. Saliva does not normally contain intrinsic factor, which is a protein produced by the stomach to aid in the absorption of vitamin B12. Saliva does contain isozymes, IgA antibodies, and lactoferrin. Isozymes are different forms of enzymes, IgA is an antibody important for immune defense, and lactoferrin is a protein with antimicrobial properties found in saliva. Therefore, D is the correct answer as intrinsic factor is not a normal component of saliva.