uworld block 7 Flashcards
urea cycle deficiencies, treatment
treatment: limit protein in diet. benzoate or pheylbutyrate bind aas and lead to excretion; lactulose acidifies GI and traps NH4+ for excretion.
1. ornithine transcarbamylase deficiency: X linked recessive. excess carbamoyl phosphate is converted to orotic acid. incr. orotic acid is found in blood and urine, decr. BUN, symptoms of hyperammonemia. no megaloblastic anemia present.
2. N-acetylglutamate deficiency: required cofactor for carbamoyl synthetase I. absence of N-acetylglutamate causes hyperammonemia. presences looks like carabmoyl synthase deficiency, but excess ornithine with normal urea cycle suggests N-acetylglutamate deficiency
describe/draw the urea cycle
see pg 108 in FA
carbamoyl phosphate synthetase I is a rate liming enzyme in the urea cycle and is activated by N-acetylglutamate, which is in turn produced from glutamate and acetyl CoA in a reaction activated by arginine.
small cell carcinoma treatment
ALWAYs radiation and chemo (or palliative)- never give surgery. this cancer basically always presents with distant mets.
How does left sided heart failure lead to pulmonary HTN?
left atrial pressures rise, and pulm venous congestion ensues. this causes hydrostatic pressures in the lung to rise dramatically. rise in hydrostatic pressures causes capillary leak and pulm edema. edema causes alveolar collapse and results in decreased ventilation, which in turn causes hypoxemia. reactive vasoconstriction occurs to shunt blood toward areas where venilation is less compromised –> pulm arterial HTN and incr. in afterload –> right heart failure.
What are pulmonary abscesses? How do they present? What causes them?
local suppurative collections within the lung parenchyma that result in necrosis of the surrounding tissue. if the abscess communicates with an air passage, the semiliquid exudate will partially drain, creating an air-containing cavity that can be seen on X-ray. histologically, there is supperative destruction of the lung parenchyma within the abscess cavity. this destruction occurs because of release of lysosomal enzymes by neutrophils and macrophages.
What is the rate-limiting step in glycogenolysis? When does it occur? What regulates this step?
occurs after 12-18 hrs of fasting. pyruvate is converted to PEP via biotin dependent carboxylation to oxaloacetate in the mitochondria. this reaction is catalyzed by pyruvate carboxylase, which is increased by acetyl-CoA. oxaloacetate is then converted to malate by malate dehydrogenase and shuttled out of the mitochondria, where it is converted back to oxaloacetate. finally, oxaloacetate is converted to phosphoenolpyruvate by phosphoenolpyruvate carboxykinase.
Alanine inhibts pyruvate kinase, which decreases glycolysis, but does NOT promote gluconeogenesis.
death cap mushroom poisons
they contain amatoxin. these toxins are concentrated in the liver and bind DNA-dependent RNA polymerase and halt mRNA synthesis, ultimately causing apoptosis. GI tract and proximal convoluted tubules may also be affected.
symptoms begin 6-24 hrs after ingestion and include abdominal pain, vomiting, and severe, cholera-like diarrheat that may contain blood and mucus. may see hepatic and renal failure. look for alpha amanitin in urine to confirm.
fomepizole
antidote for methanol or ethylene glycol poisoning. competitive antagonist of alcohol dehydrogenase that prevents the converstion of methanol and ethylene glycol to toxic metabolites
how do you prevent nephrotoxicity in cisplatin therapy?
give amifostine. it is a thiol based cytotprotective free-radical scavaging agent . also use chloride diureses becasue cisplatin stays in nonreactive state when in a higher chloride concentration.
How do free fatty acids influence glucose levels?
high free fatty acids can cause insulin resistance and decrease insulin secretion. this is called “lipotoxicity.”
legionella: culture medium, illness
seen with silver stains and demonstrates slow growth on complex media like charcoal-yeast extract with cysteine. causes nosocomial pneumonias associated with contaminated water supply
What do cephalosporins bind?
they irreversibly bind penicillin binding proteins. transpeptidases are one kind of PBP that cross link peptidoglycan in the cell wall.
treatment of TCA toxicity
TCAs can cause QRS and QT prolongation and cause cardiac dysrhythmias due to inhibition of fast sodium channels. to treat CV toxicity from TCA overdose, give NaHCO3.
What causes orange peel appearance of breast, physiologically? What about skin dimpling and nipple investion?
orange peel: dermal lymphatic obstruction by cancer cells. esp. common in pts with inflammatory breast cancer.
nipple inversion: tumor invasion of central breast; skin retraction when the cancer infiltrates the suspensory cooper ligaments.
Sheehan syndrome
high estrogen levels during pregnancy stimulate the growth of the pituitary, but the blood supply doesn’t increase with it. if significant hypotension occurs when the pituitary is enlarged (ie. post-partum hemorrhage), the pituitary will die (ischemic necrosis). prolactin deficiency is common, as is hypothyroidism and hypocortisolism.
