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USMLE World Missed Questions > Deck X > Flashcards

Flashcards in Deck X Deck (30):
1

How is muscle contraction different in cardiac myocytes compared to skeletal muscle cells?

In skeletal muscle cells, contraction is dependent on both proteins (myosin II, actin, tropomyosin, and troponin) as well as calcium ions.

2

What is the length constant in neuronal conduction?

A measurement of how far along an axon an electrical impulse can propagate; a low length constant reduces the distance an impulse can travel.

3

Why is skeletal muscle resistant to the effects of calcium channel blockers?

Because skeletal muscle does not require an influx of extracellular calcium for excitation-contraction coupling; cardiac and smooth muscle depend on extracellular calcium entering the cell via voltage gated L-type calcium channels for excitation contraction coupling. These channels are the target of Ca2+ channel blockers.

4

Describe the sites and amounts of potassium resorption in the nephron.

K+ is freely filtered across the glomerular membrane; 2/3 of the filtered load is then reabsorbed in the proximal tubule; the thick ascending limb further resorbs 25-30%. Th late distal and cortical collecting tubules are the primary mediators of potassium regulation and are the primary sites of K+ reabsorption

5

How does cortisol interact with catecholamines in terms of vascular reactivity?

Cortisol augments the vasoconstrictive effects of catecholamines; cortisol has permissive effects on catecholamines by allowing them to achieve their full vasoconstrictive potentials

6

What are the two principle actions of ANP (atrial natriuretic peptide)?

Peripheral vasodilation and increased urinary excretion of sodium and water.

7

Which thyroid hormone is produced in the greatest quantity?

T4

8

Which thyroid hormone is the most active form?

T3 (rT3 is inactive)

9

How is T4 converted to T3?

By deiodinase enzymes into T3 and rT3

10

How many calories per gram are generated in protein/carbohydrate, fat, and ethanol metabolism?

carbohydrate/ protein = 4 cal/ gram; fats 9 cal/ gram; ethanol 7 cal/gram of energy

11

What serum marker reflects osteoblastic activity?

Bone specific alkaline phosphatase

12

Name three serum markers that reflect osteoclastic activity.

Tartrate-resistant acid phosphatase, urinary hydroxyproline, urinary deoxypyridonoline

13

Where are androgens that are synthesized in the ovaries converted into estradiol?

LH stimulates the theca interna cells of the ovarian follice to produce androgens that are converted to estradiol in granulosa cells via aromatase in a reaction stimulated by FSH.

14

What enzyme catalyzes activation of trysinogen to trypsin?

Enteropeptidase (or enterokinase) secreted from the duodenum.

15

What type of compound is D-xylose?

A carbohydrate.

16

Which dietary compounds can be readily absorbed by the intestine without pancreatic enzymes?

carbohydrates.

17

What type of drug is diphenoxylate?

Opiate anti-diarrheal.

18

In ascites, esophageal varices are the result of chronic shunting of portal blood to systemic circulation through which vein?

Left gastric vein (to esophageal vein)

19

In ascites, hemorrhoids are the result of chronic shunting of portal blood to systemic circulation through which vein?

Superior Rectal Vein (to middle and inferior rectal veins)

20

In ascites, caput medusae are the result of chronic shunting of portal blood to systemic circulation through which vein?

Paraumbilical veins (to superficial and inferior epigastric veins)

21

What pathology is associated with H. pylori antral gastritis?

Duodenal ulcers caused by unchecked gastrin production due to destruction of somatostatin secreting cells in the gastric antrum.

22

What malignancies are associated with H. pylori infection?

Gastric adenocarcinoma and gastric lymphoma.

23

What are the clinical manifestations of a leptin gene or receptor mutation?

Human obesity and hyperphagia

24

What is leptin?

Protein hormone produced by adipocytes in proportion to stored fat quantity; it acts on the arcuate nucleus of the hypothalamus to inhibit production of neuropeptide Y and to stimulate production of a-MSH which decrease appetite and increase satiety respectively

25

Where is the most common location for intussuception?

Ileocolic junction.

26

What is the mechanism of action of statins?

Inhibition of HMG CoA reductase; in response to these changes, hepatocytes increase surface expression of the LDL receptor to increase uptake of circulating LDL

27

What causes pancreatic autodigestion in acute necrotizing pancreatitis?

Damage to the pancreatic acinar cells triggers abnormal activation of trypsin inside the acinar cells by lysosomal enzymes. Trypsin then activates other proteolytic enzymes causing pancreatic autodigestion.

28

What is the most common benign liver tumor?

Cavernous hemangioma

29

How do cavernous hemangiomas appear microscopically?

As cavernous, blood filled vascular spaces of variable size, lined by a single epithelial layer.

30

Which types of liver tumors are associated with oral contraceptive use and may regress with discontinuation?

Hepatic adenomas.