Which of these statements about bile is true?

Correct Answer: D

Rationale: Step 1: Bile is produced in the liver, not the gallbladder. Step 2: Bile salts aid in digestion by emulsifying fats. Step 3: Bile salts are recycled in the enterohepatic circulation. Step 4: This recycling process conserves bile salts. Step 5: Choice D is correct as it accurately states that bile salts are recycled, supporting efficient digestion and absorption.

Correct Answer: B

Rationale: The correct answer is B: small intestine. Digestive enzymes are activated in the small intestine to break down nutrients. Firstly, enzymes are secreted by the pancreas into the small intestine, where they act on carbohydrates, proteins, and fats. Secondly, bile from the liver helps in the digestion of fats. The stomach mainly secretes gastric juices for protein digestion, not enzymes for overall digestion. The liver produces bile, not digestive enzymes. The pancreas secretes various digestive enzymes, but they become activated in the small intestine.

Correct Answer: A

Rationale: The correct answer is A: Parietal cells. Parietal cells secrete hydrochloric acid in the stomach to create the acidic environment necessary for digestion. They also secrete intrinsic factor for vitamin B12 absorption. Chief cells produce pepsinogen, not hydrochloric acid. Mucous neck cells secrete mucus to protect the stomach lining. Enteroendocrine cells secrete hormones like gastrin, not hydrochloric acid. Therefore, the correct choice is A as it directly produces hydrochloric acid in the stomach.

Correct Answer: C

Rationale: The correct answer is C because the defecation reflex is integrated in a control center in the sacral spinal cord. This is due to the presence of the parasympathetic nerves that control the smooth muscles of the colon and rectum in the sacral region. The sacral spinal cord is responsible for coordinating the reflexive relaxation of the internal anal sphincter and contraction of the rectum during defecation. Choices A and B are incorrect because the initiation and integration of the defecation reflex do not involve the anal canal stretching or the lumbar spinal cord. Choice D is incorrect as the defecation reflex is not controlled by the vagus nerve, which is primarily responsible for the parasympathetic innervation of organs in the thorax and upper abdomen.

Correct Answer: C

Rationale: The correct answer is C: Lactase. Lactase is an enzyme produced in the small intestine, not in the pancreas. The exocrine pancreas secretes digestive enzymes like chymotrypsinogen, proelastase, and lipase to aid in the digestion of proteins, fats, and carbohydrates. Lactase is responsible for breaking down lactose, a sugar found in dairy products, and is produced in the small intestine. Therefore, C is the correct answer. Choices A, B, and D are incorrect because chymotrypsinogen, proelastase, and alph are all enzymes produced by the pancreas to aid in digestion.