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24 Cards in this Set

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describe the structure of heme.
porphyrin ring (19C's and 4N's in the middle which binds iron) and surrounded by 4 porphobilinogens with propyl, methyl, and vinyl groups.
describe the roles of heme in the body. (more)
prosthetic moiety of numerous hemoproteins essential for the fxn of all aerobic cells. Includes Hb, Mb, oxidases, peroxidases, catalases, cytochromes, some signalling molecules, steroid, nitric oxide.
describe where heme biosynthesis takes place
8 steps, first and last two in mito, rest in cytoplasm
where does lead inhibit heme biosynth
steps 2 and 8 (stops ala dehydratase and ferrochelatase)
in non erythroid tissues, how does heme regulate its synthesis
inhibiting both txn of ALA synthesis (aminolevulinic acid) and transport of the enzyme into the mitochondria, thus providing feedback regulation. The 1st step is the rate limiting step
describe the genes for ALA synthase
two genes for the erythroid specefic form and the ubiquitous housekeeping form
what are the three upregulators of ALA synthestase 1?
lipophilic drugs and chemicals that interact with nuclear receptors and thus increase activation of RES in the enhancer of ALA-synth 1. def of glucose or gluconeogenic compounds that regulate geneexpression of ALA synth 1, def of heme and thus no repression of txn of ALA synthase 1 and translocation of the enzyme into the mitochondria and increased the stability of ALA S1 mRNA
describe the regulation of ALA-S2, the erythroid form.
post transcriptional via an iron response element (regulatory step) - in presence of iron we get txn by removing IRE from the message, many cis elements, and txn is stimulated by heme.
what are the acute porphyrias?
inborn errors of heme biosynthesis
how are the porphyrias classified?
hepatic or erythroid. Or cutaneous or acute (neuro visceral)
3 facts on porphyrias.
more commen in women. Treatment restores heme homeostasis. Most are AD
symptoms of acute porphyria.
usually from hepatic cells, get accumulation of ALA and PBG, thought to be neurotoxic
where is heme synthesis most abundant?
erythroid cells first then liver cells
all cells except what can degrade heme?
mature RBCs
rate limiting step of heme synth?
succinyl CoA and glycine condense to form ALA via ALA synthase
ways to test for porphyrias?
enzyme activity and DNA analysis
treatment for an acute attack?
nutritional support, seizure precautions if hyponatremic, IV fluids, narcotics, phenothiazine for GI issues, beta blockers for hypertension and tachycardia, IV glucose may resolve mild attacks, begin hemin ASAP
describe the heme catabolic pathway and excretion (more)
heme oxygenase oxidizes NADPH and splits open the porphyrin ring and releases iron 3 and CO. Open ring is called biliverdin which is reduced by biliverdin reductase (oxidizes another NADPH). Now we have bilirubin which hitches a ride on albumin and goes to the liver. In hepatocytes, it undergoes conjugation via glucuronyl bilirubin transferase. conjugated bilirubin goes to the hepatic ducts to the bile. bilirubin diglucuronide (conjugated bilirubin) is hydrolized and reduced by bacteria in the gut to yield urobiliogen which is colorless. some urobilinogen is reabsorbed to the portal blood and goes to the kidney where it is converted to yellow urobilin and excreted giving urine its characteristic color. Most urobilinogen of feces is reduced by intestinal bacteria to stercobilin which gives stools their characteristic brown color.
where does the heme oxygenase step in heme catabolism take place?
in macs
describe hemolytic jaundice
massive lysis of RBCs like in sickle cell or malaria may make bilirubin faster than the liver can conjugate it. More bilirubin is excreted into the bile thus more urobilinogen re enters circulation and more is in the urine. All this leads to increase in blood unconjugated bilirubin
describe obstructive jaundice
jaundice from obstruction of the bile duct. Perhaps by a hepatic tumor or bile stones. Liver regurgitates conjugated bilirubin into the blood which is excreted in the urine. Pts have GI pain, nausea, dark urine and pale stools.
describe hepatocellular jaundice
liver cells are damaged and causes a decrease in both bilirubin uptake and conjugation thus unconjugated bilirubin occurs in the blood and increased urobilinogen in the urine, dark urine and pale stools
describe kernicterus, its treatment, and those at risk.
excess bilirubin that is in the plasma and not bound to albumin can cause toxic encephalopathy called kernicterus, treat with a blue fluorescent light which converts bilirubin to more polar and more water soluble isomers that can be excreted.. Newborn infants, particularly premies are at risk.
other names for conjugated and unconjugated bilirubin.
direct and indirect