The hydrogen ions that form hydrochloric acid of the stomach come from

Correct Answer: B

Rationale: The correct answer is B: carbonic acid. Carbonic acid is produced when carbon dioxide reacts with water in the stomach, forming hydrogen ions that combine with chloride ions to create hydrochloric acid. Lactic acid (A), citric acid (C), and acetic acid (D) do not directly contribute to the formation of hydrochloric acid in the stomach. Therefore, they are incorrect choices for this question.

Correct Answer: B

Rationale: The correct answer is B: colon. The colon is characterized by having a simple columnar epithelium in its tunica mucosa, smooth muscle in its tunica muscularis, and epiploic appendages attached to its outer surface. The cecum (A) is a pouch-like structure at the beginning of the large intestine. The rectum (C) is the final segment of the large intestine before the anal canal (D). The anal canal is lined by stratified squamous epithelium, not simple columnar epithelium like the colon.

Correct Answer: C

Rationale: The correct answer is C (7-9) because trypsin and chymotrypsin are proteolytic enzymes that function optimally in slightly basic environments. At pH 7-9, these enzymes maintain their structural integrity and catalytic activity. Choices A, B, and D are incorrect because trypsin and chymotrypsin are not acidic enzymes, so pH ranges 1-3 and 10-12 would denature and inactivate them, while pH 5-7 is still on the acidic side, not optimal for these enzymes.

Correct Answer: D

Rationale: Sure! Here is a step-by-step rationale for why answer choice D is correct: P. Mechanical digestion occurs in the stomach: This statement is correct as the stomach performs mechanical digestion through the churning and mixing of food with gastric juices. Q. Cholecystokinin, gastrin, and secretin are produced by enteroendocrine cells: This statement is correct as these hormones are indeed produced by enteroendocrine cells to regulate various digestive processes. R. Pancreas, small intestine, and salivary glands produce digestive enzymes: This statement is correct as these organs are key producers of digestive enzymes essential for breaking down food components. S. Mucous neck cells, chief cells, parietal cells are present in the stomach: This statement is correct as these are the types of cells found in the gastric glands of the stomach responsible for producing mucus, pepsinogen, and hydrochloric acid, respectively. In summary, all the statements in answer choice D

Correct Answer: C

Rationale: The correct answer is C because amino acids are not absorbed through the stomach wall; they are absorbed in the small intestine. In the stomach, gastric juices break down proteins into peptides. Option A is incorrect because the stomach secretes pepsin to digest proteins. Option B is also incorrect as pepsinogen is converted to pepsin for protein digestion. Option D is incorrect since ghrelin, the appetite hormone, is indeed released by the stomach.