The principal function for cells lining the sides of intestinal crypts of Lieberkühn is:

Correct Answer: D

Rationale: The correct answer is D because cells lining the sides of intestinal crypts of Lieberkühn are responsible for supplying replacement cells for the epithelium of villi. These cells undergo rapid division and differentiation to replace the cells shed from the villi, ensuring the continuous renewal and maintenance of the intestinal lining. This process is crucial for the absorption of nutrients and maintaining the integrity of the intestinal barrier. Choice A (secreting digestive enzyme) is incorrect because the cells in the intestinal crypts primarily function in cell replacement, not enzyme secretion. Choice B (secreting one of several various hormones) is incorrect as the main function of these cells is not hormone secretion but rather cell turnover. Choice C (secreting mucus) is incorrect as mucus secretion is typically associated with other specialized cells in the intestinal lining, such as goblet cells, not the cells in the crypts responsible for cell replacement.

Correct Answer: B

Rationale: The correct answer is B: central vein. The hepatic lobule is a structural unit of the liver, consisting of hepatocytes arranged in a hexagonal pattern around a central vein. Hepatocytes receive oxygenated blood from the hepatic artery and nutrient-rich blood from the portal vein. These blood vessels merge within the lobule, and the blood flows towards the central vein. Bile produced by hepatocytes drains into bile canaliculi and eventually into bile ducts, which are not directly associated with defining the hepatic lobule. Therefore, the central vein is the correct answer as it is the vessel that receives blood from the sinusoids in the lobule.

Correct Answer: A

Rationale: The correct answer is A: hepatocytes. The term liver parenchyma refers to the functional cells of the liver responsible for its essential functions, such as metabolism, detoxification, and synthesis. Hepatocytes make up the majority of the liver's mass and are crucial for its normal functioning. Portal veins and hepatic arteries (choice B) are blood vessels supplying the liver, bile ducts (choice C) are responsible for transporting bile, and stored glycogen (choice D) is a form of stored energy in the liver, but they do not specifically refer to the liver parenchyma.

Correct Answer: D

Rationale: The correct answer is D: breakdown of hemoglobin. Hepatocytes do not breakdown hemoglobin; this function occurs primarily in the spleen. A: drug detoxification is correct as the liver metabolizes and detoxifies drugs. B: protein synthesis is also correct as hepatocytes produce various proteins. C: gluconeogenesis is correct as the liver can synthesize glucose from non-carbohydrate sources. Therefore, the breakdown of hemoglobin is the only function not performed by hepatocytes.

Correct Answer: B

Rationale: The gall bladder is best understood as a specialized region of a duct. It stores and concentrates bile produced by the liver, releasing it into the small intestine for digestion. The gall bladder is anatomically connected to the bile duct system. Choices A, C, and D are incorrect because the gall bladder is not a lymph node (A), adipose tissue (C), or hepatocyte parenchyma (D). The gall bladder's main function is related to bile storage and release, making it a specialized region of a duct system.