Deck XIV Flashcards Preview

USMLE World Missed Questions > Deck XIV > Flashcards

Flashcards in Deck XIV Deck (30):

In a-fib, what regulates the number of atrial impulses that reach the ventricle?

The AV node refractory period determines the number of impulses that reach the ventricle and determines ventricular contraction rate.


What is hepcidin?

An acute phase reactant synthesized by the liver that acts as the central regulator of iron homeostasis


What is ferroportin?

A transmembrane protein responsible for transferring intracellular iron to circulation.


Describe the two paths for iron once inside the intestinal cells.

1. it may bind to ferritin to be stored within an enterocyte. It is excreted in the stool as enterocytes slough off and are replaced; 2. It may enter circulation through ferroportin; free iron in circulation is transported by transferrin.


How is hepcidin synthesized?

By hepatic parenchymal cells. Synthesis is increased in inflammatory conditions and is lowered in states of hypoxia and erythropoiesis.


How do low hepcidin concentrations affect iron absorption?

Low hepcidin levels increase intestinal iron absorption and stimulate iron release by macrophages.


In Burkitts lymphoma, what gene is translocated and what is its function?

Translocation of the c-myc oncogene on the long arm of chromosome 8 with the Ig heavy chain region on chromosome 14. C-myc is a nuclear phosphoprotein that functions as a transcription factor which controls cell proliferation, differentiation, and apoptosis.


What is deficient in a patient with acute intermittent porphyria?

Porphobilinogen (PBG) deaminase deficiency


How does acute intermittent porphyria present?

Acutely with GI and neurologic symptoms, most commonly abdominal pain, vomiting, peripheral neuropathy, neuropsych derangements. Key feature is reddish urine that darkens on exposure to light and air due to oxidation of excess PBG.


What is the target of treatment and prevention of acute porphyria attacks?

Inhibition of ALA synthase (rate limiting enzyme of heme synthesis) to reduce formation of toxic intermediate metabolites. Avoid CYP450 inducers, alcohol, smoking; tx with IV heme administartion and carbohydrate loading such as dextrose infusion.


How does CO affect PaO2?

It does not affect this value. It only affects the amount of oxygen that can bind to hemoglobin and PaO2 in CO poisioning is typically normal.


What side effects are associated with ticlopidine?

Neutropenia, fever, mouth ulcers.


Auer rods are found in what type of cells?

Myeloblasts in AML


What is the mechanism of Heparin?

It increases the effect of antithrombin III.


What is measured to monitor the therapeutic effect of heparin?

aPTT (activated partial thromboplastin time).


What is protamine sulfate used to treat?

Heparin toxicity (not effective in LMW heparins)


What is the function of aminocaproic acid treatment?

To inhibit fibrinolysis.


To what drug class does enoxaparin belong?

Low molecular weight heparin. It functions by binding and activating antithrombin III.


How does antithrombin III produce an anticoagulant effect?

By reducing thrombin production through binding to factor Xa to stop the conversion of prothrombin to thrombin.


What adverse effects are associated with Non-nucleotide RT inhibitors?

Abrupt flulike symptoms, abdominal pain, jaundice, fever may indicate hepatic failure and encephalopathy. These effects are most common within the first 6 weeks of therapy. Stevens- Johnson syndrome has also been observed.


How are nonnucleoside reverse transcriptase inhibitors (NNRTIs) activated?

They do not require activation via intracellular phosphorylation.


Name the three most common NNRTI drugs.

Nevirapine, efavirenz, delavirdine.


HIV fusion inhibitor drugs function by what mechanism?

Selective binding to HIVs transmembrane envelope protein gp41


What is the mechanism of action of enfuvirtide?

Binds to the heptad repeat 1 (HR1) of gp41 preventing gp41 from undergoing conformational changes necessary for viral membrane fusion with the target cellular membrane. This denies HIV genome entry into uninfected CD4+ T cells.


What is the mechanism of action of aspirin?

Irreversible inhibition of COX1 and COX2 through acetylation of the COX enzymes. At low doses, aspirin inhibits COX1 alone but at high doses it inhibits both COX 1 and COX2.


What drug is used to terminate early (<6 weeks gestational age) ectopic pregnancies?



What does methotrexate inhibit?

Competitive and irreversible inhibition of dihydrofolate (DHF) reductase. This causes accumulation of dihydrofolic acid polyglutamate within treated cells.


Where in the prostate does prostate adenocarcinoma typically originate?

The peripheral zone of the prostate and can thus be detected on digital rectal examination as an asymmetric nodular enlargement of the prostate.


What is characteristic of a peripheral blood smear in a patient with lead poisioning?

Coarse basophilic stippling on the background of hypochromic microcytic anemia. Basophilic stippling is the result of ribosome aggregation.


What is inhibited in lead poisioning?

delta-ALA dehydratase. This causes reduced incorporation of iron into heme and decreased hemoglobin synthesis.