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Correct Answer: B

Section: Physiology True mean arterial pressure cannot be determined without a pressure transducer, which averages the systolic and diastolic pressures throughout the cardiac cycle. However, mean arterial pressure can be estimated by adding one-third of pulse pressure to the minimum diastolic pressure. At rest his mean pressure is 30/3 + 75 = 85; during exercise mean pressure is 75/3 + 65 = 90. Hence, estimated mean pressure increased by 5 mm Hg.

Correct Answer: C

Section: Biochemistry During early fasting, as the level of glucose in the blood falls, the pancreas releases glucagon into the circulation to counter this drop. The major site of glucagon action is the liver. There it induces the activity of the glycogen phosphorylase leading to an increase in glucose release from glycogen stores. Thus, an inhibition of glycogen phsphorylase would limit the ability of the liver to provide glucose to the blood. Negatively affecting the activity of glycogen phosphorylase would not significantly affect the rate of hepatic fatty acid oxidation (choice A), skeletal muscle glucose usage (choice D), nor hepatic gluconeogenesis (choice E). The liver may have a reduced capacity for de novo storage of glucose following meals (choice B) due to a prior reduction in the release of glucose via the inhibition of glycogen phosphorylase; however, on fasting there would still be a reduction in glucose release.

Correct Answer: D

Section: Biochemistry The binding of acetylcholine to its receptor at the neuromuscular junction results in depolarization of the muscle membrane. This event triggers the release of calcium ions from the sarcoplasmic reticulum. The increase in intracellular calcium concentration leads to many changes in enzyme activity. One effect of calcium is that it is bound by various calciumregulated binding proteins. One of the subunits of glycogen phosphorylase kinase is calmodulin, a calcium-binding protein. The interaction of calcium with calmodulin alters the conformation of calmodulin, which leads to an activation of glycogen phosphorylase kinase activity in the absence of phosphorylation. The activity of glycogen phosphorylase kinase is increased not decreased (choice A) by calcium interaction with calmodulin present in the enzyme complex. Increases in intracellular calcium (as in response to acetylcholine binding at the neuromuscular junction) do not affect the level of phosphorylation of glycogen phosphorylase kinase (choices B and E) nor does it affect the activity of phosphoprotein phosphatase (choice C).

Correct Answer: A

Correct Answer: E

Section: Microbiology/Immunology The viridans streptococci include S. mitis, S. mutans, S. salivarius, S. sangus, and others. They make up a major part of oral normal flora and are alpha hemolytic. They reach the bloodstream as a result of trauma and are a principal cause of endocarditis on abnormal heart valves (choice E). They produce large amounts of polysaccharides and contribute to dental caries. S. aureus (choice B) and S. epidermidis (choice C) are usually found on the skin and may be opportunistic, but they are not as significant for endocarditis as the alpha hemolytic streptococci. E. faecalis (choice A) are usually found in the intestinal tract flora and are opportunistic if they escape that location. The major lesion for enterococci is an abscess. S. pneumonia (choice D) is primarily found in lung infections (pneumonias) and are pathogenic primarily due to their polysaccharide capsules which inhibit phagocytosis.