Correct Answer: E

Section: Anatomy Arrow 1 points to the superior vena cava. The central venous catheter is inserted into the subclavian vein and threaded into the superior vena cava. The ascending aorta (choice A) is labeled by arrow 4 and its counterpart, the descending aorta (choice C) by arrow 5. The azygos vein (choice B) is indicated by arrow

1. Arrow 2 indicates the right bronchus (choice D) just as it leaves the carina.

Correct Answer: D

Section: Biochemistry Osteogenesis imperfecta consists of a group of at least four types (mild, extensive, severe, and variable). The disorder is characterized by brittle bones and abnormally thin sclerae, which appear blue owing to the lack of connective tissue. The symptoms arise due to defects in two alpha-collagen genes, the COL1A1 and COL1A2 genes. There have been over 100 mutations identified in these two genes. The mutations lead to decreased expression of collagen or abnormal pro1 proteins. The abnormal proteins associate with normal collagen subunits, which prevents the triple helical structure of normal collagen to form. Theresult is degradation of all the collagen proteins, both normal and abnormal. Ehlers-Danlos syndrome (choice A) comprises at least 10 defined types of a related disorder. Characteristic clinical features are easy bruising, markedly soft hyperextensible skin, extreme joint hypermobility, and the formation of thin, atrophic, "cigarette-paper" scarring following injury. Marfan syndrome (choice B) results in cardiovascular, musculoskeletal, and ophthalmic abnormalities. Hallmark clinical manifestations are aortic dilation, mitral valve prolapse, dissecting aneurysms, arachnodactyly, and ectopia lentis. Occipital horn syndrome (choice C), a disorder that manifests with symptoms similar to other collagen metabolism disorders, results from defects in copper metabolism. Clinical features include loose skin and joints, hernias, and abnormally shaped bones. Scurvy (choice E), which is caused by a deficiency in vitamin C, is characterized by decreased wound healing and hemorrhaging, anemia, osteoporosis, soft swollen gums, and easily bruised skin.

Correct Answer: C

Section: Biochemistry The major substrates of gluconeogenesis are pyruvate and lactate. During gluconeogenesis lactate is oxidized to pyruvate. For pyruvate to be converted back to glucose, it must first be carboxylated to oxaloacetate, since a reversal of the PK reaction of glycolysis cannot occur to convert the pyruvate to phosphoenolpyruvate. The carboxylation of pyruvate is catalyzed by the mitochondrial enzyme pyruvate carboxylase. The activity of pyruvate carboxylase is absolutely dependent on the presence of acetyl-CoA, which allosterically activates the enzyme. Of the enzymes listed, only pyruvate carboxylase and PEPCK (choice B) are involved in gluconeogenesis. ACC (choice A) is involved in fatty acid synthesis and is not regulated by acetyl-CoA. PDH (choice D) is the entry point for pyruvate into the TCA cycle. It is also inhibited by acetyl- CoAvia the acetyl-CoA-mediated activation of PDH kinase, an enzyme that phosphorylatesand inactivates PDH. PK (choice E) is a glycolytic enzyme and is inhibited by acetyl-CoA, not activated by it.

Correct Answer: B

Section: Pathology and Path physiology The fine-needle biopsy shown in figure demonstrates a fairly monomorphic population of small, mitotically active neoplastic lymphocytes with associated starry sky histiocytes. The morphology of the tumor and the clinical history are typical for endemic Burkitt lymphoma. The diagnosis of adenocarcinoma (choice A) is incompatible with the photograph because malignant epithelial elements are not seen. Chronic lymphocytic leukemialymphoma (choice C) is distinctly uncommon in children and features mature lymphocytes without a starry sky background. There are no parasitic elements (choice D) evident in the photograph. Salivary gland lymphoepithelioma (choice E) is usually seen in an older age group, contains some remaining epithelial elements, and has larger immunoblastic-type lymphocytes.

Correct Answer: C

Section: Pharmacology Hepatic intracellular cholesterol levels are tightly controlled through regulation of endocytotic uptake of cholesterol within LDL particles, de novo synthesis of cholesterol, incorporation into VLDL particles, and loss due to conversion to bile acids. Inhibition of cholesterol biosynthesis through statin inhibition of the enzyme 3-hydroxymethylglutaryl- CoA reductase (HMG-CoA reductase) lowers intracellular cholesterol levels. This lowering results in increased expression of the genes for the LDL receptor and HMG-CoA reductase. Increased expression of LDL receptors leads to increased endocytic uptake of LDL particles from the blood and consequent reduction of circulating levels of LDL cholesterol. Choice D is incorrect because the statins do not affect hepatic VLDL secretion. Inhibition of VLDL secretion is probably the mechanism of action for nicotinic acid in lowering VLDL and LDL. Choice E is incorrect because the statins do not affect lecithin:cholesterol acyltransferase (LCAT) activity. Binding to PPAR-alpha and activation of lipoprotein lipase (choice A) appears to be the mechanism for lowering elevated VLDL levels by the fibric acids such as gemfibrozil. Bile acid- binding resins such as cholestyramine promote increased fecal excretion of bile acids (choice B) and ultimately lead to increased expression of hepatic LDL receptors.