Which part of a tooth most closely resembles bone tissue?

Correct Answer: C

Rationale: The correct answer is C: dentin. Dentin is the part of the tooth that closely resembles bone tissue because it is a hard, dense tissue similar to bone in composition and structure, providing support and protection to the tooth. Dentin is located beneath the enamel and cementum, forming the bulk of the tooth structure. Enamel (choice A) is the hardest tissue in the body but is not similar to bone tissue in composition. Cementum (choice B) is a hard tissue covering the roots of teeth but is not as similar to bone tissue as dentin. Gingiva (choice D) is the soft tissue that surrounds the teeth and is not similar to bone tissue.

Correct Answer: A

Rationale: The correct answer is A: Vitamin C. Vitamin C is water-soluble and not stored in the liver. It gets absorbed in the intestines and any excess is excreted in the urine. Vitamin D (choice B) is fat-soluble and stored in the liver. Vitamin B12 (choice C) is also stored in the liver. Vitamin A (choice D) is fat-soluble and stored in the liver as well. Thus, the correct answer is A as it is the only water-soluble vitamin among the options.

Correct Answer: A

Rationale: The correct answer is A: sinusoids. Sinusoids are specialized blood channels found in the liver that allow for the exchange of nutrients, waste products, and toxins between hepatocytes and blood. They play a crucial role in the liver's functions of detoxification, metabolism, and storage. Central vein (B) is a vessel located in the center of liver lobules, not a blood channel. Hepatic cells (C) refer to the liver cells themselves, not blood channels. Portal veins (D) are vessels that bring blood from the digestive organs to the liver, but they are not the special blood channels within the liver.

Correct Answer: B

Rationale: The correct answer is B: large intestine. The small intestine, plicae circulares, and crypts of Lieberkuhn are all structures found in the small intestine, involved in absorption and digestion. The large intestine is a separate part of the digestive system primarily responsible for water absorption and waste elimination. Therefore, it does not belong with the other choices related to the small intestine.

Correct Answer: B

Rationale: The correct answer is B (stomach) because amylase is an enzyme that breaks down carbohydrates, and it is primarily found in the mouth and the small intestine (duodenum and pancreas). In the mouth, salivary amylase begins the digestion of starches. In the small intestine, pancreatic amylase continues this process. The stomach, however, is not a site for amylase secretion but rather secretes pepsin for protein digestion. Therefore, amylase is not found in the stomach. Choices A, C, and D are incorrect because amylase is indeed present in the mouth, duodenum, and pancreas, respectively.