Semitallsmalls
04-18-2007, 06:55 PM
Thiamine is HY for the USMLE Step 1 (http://hy4theusmle.blogspot.com/2007/04/thiamine-is-hy-for-usmle-step-1.html)
THIAMINE aka Vitamin B1
Active form: Thiamine Pyrophosphate (TPP)
Main reactions in which thiamine is a cofactor:
http://bp3.blogger.com/__tCY80jlSj0/RiU-ccpnFFI/AAAAAAAAAFk/l7IgwgBTHTA/s320/Oxidative+decarboxylation+in+TCA.jpg (http://bp3.blogger.com/__tCY80jlSj0/RiU-ccpnFFI/AAAAAAAAAFk/l7IgwgBTHTA/s1600-h/Oxidative+decarboxylation+in+TCA.jpg)These dehydrogenase reactions generate NADH in the mitochondria which enter the electron transport chain to generate ATP, therefore the patient has a problem making ATP.
Cofactors required by the above 2 enzymes are
Thiamine
Lipoic acid
CO2
Folate
NAD+
Which can be remembered by the phrase, "Tender Love and Care for Nancy"
(Thiamine is also a cofactor for transketolase which catalyzes 2 Carbon transfers in the HMP shunt (pentose phosphate pathway) - required to make Ribose 5 phosphate for nucleotide synthesis)
Classic patient is a Malnourished Alcoholic
Signs and symptoms of deficiency:
Wernicke's Encephalopathy
http://bp0.blogger.com/__tCY80jlSj0/RiU_fspnFGI/AAAAAAAAAFs/1w3ezgpWD3U/s320/Wernicke%27s.jpg (http://bp0.blogger.com/__tCY80jlSj0/RiU_fspnFGI/AAAAAAAAAFs/1w3ezgpWD3U/s1600-h/Wernicke%27s.jpg)
Peripheral neuropathy
due to Wallerian degeneration; not drawn (source: Boards and Wards, 3rd Edition)
occurs since ATP is needed for myelin production and ATP isn't being made to the same quantity
Neuropathy may manifest as foot drop or wrist drop much like lead poisoning does in adults
Wernicke's encephalopathy is reversible (We-versible Wernicke's)
________
Say the above patient was given glucose without correcting his thiamine deficiency, it would precipitate...
Korsakoff's Amneisa
These are the Mammillary Bodies:
http://bp2.blogger.com/__tCY80jlSj0/RiVAAMpnFHI/AAAAAAAAAF0/x0JFt8YKHUM/s320/harp3a.jpg (http://bp2.blogger.com/__tCY80jlSj0/RiVAAMpnFHI/AAAAAAAAAF0/x0JFt8YKHUM/s1600-h/harp3a.jpg)
These are the mammillary bodies on drugs:
http://docs.google.com/File?id=ajcs9hf8jc8n_47frpxq4
Any questions?
(source: The Medical Journal of Australia (http://www.mja.com.au/public/issues/jun1/harper/harper3.html) )
anterograde and retrograde amnesia
Bilateral hemorrhagic necrosis of mammillary bodies
mammillary bodies are in the hypothalamus and are part of the limbic system
irreversible
Treatment: IV Thiamine and THEN glucose
THIAMINE aka Vitamin B1
Active form: Thiamine Pyrophosphate (TPP)
Main reactions in which thiamine is a cofactor:
http://bp3.blogger.com/__tCY80jlSj0/RiU-ccpnFFI/AAAAAAAAAFk/l7IgwgBTHTA/s320/Oxidative+decarboxylation+in+TCA.jpg (http://bp3.blogger.com/__tCY80jlSj0/RiU-ccpnFFI/AAAAAAAAAFk/l7IgwgBTHTA/s1600-h/Oxidative+decarboxylation+in+TCA.jpg)These dehydrogenase reactions generate NADH in the mitochondria which enter the electron transport chain to generate ATP, therefore the patient has a problem making ATP.
Cofactors required by the above 2 enzymes are
Thiamine
Lipoic acid
CO2
Folate
NAD+
Which can be remembered by the phrase, "Tender Love and Care for Nancy"
(Thiamine is also a cofactor for transketolase which catalyzes 2 Carbon transfers in the HMP shunt (pentose phosphate pathway) - required to make Ribose 5 phosphate for nucleotide synthesis)
Classic patient is a Malnourished Alcoholic
Signs and symptoms of deficiency:
Wernicke's Encephalopathy
http://bp0.blogger.com/__tCY80jlSj0/RiU_fspnFGI/AAAAAAAAAFs/1w3ezgpWD3U/s320/Wernicke%27s.jpg (http://bp0.blogger.com/__tCY80jlSj0/RiU_fspnFGI/AAAAAAAAAFs/1w3ezgpWD3U/s1600-h/Wernicke%27s.jpg)
Peripheral neuropathy
due to Wallerian degeneration; not drawn (source: Boards and Wards, 3rd Edition)
occurs since ATP is needed for myelin production and ATP isn't being made to the same quantity
Neuropathy may manifest as foot drop or wrist drop much like lead poisoning does in adults
Wernicke's encephalopathy is reversible (We-versible Wernicke's)
________
Say the above patient was given glucose without correcting his thiamine deficiency, it would precipitate...
Korsakoff's Amneisa
These are the Mammillary Bodies:
http://bp2.blogger.com/__tCY80jlSj0/RiVAAMpnFHI/AAAAAAAAAF0/x0JFt8YKHUM/s320/harp3a.jpg (http://bp2.blogger.com/__tCY80jlSj0/RiVAAMpnFHI/AAAAAAAAAF0/x0JFt8YKHUM/s1600-h/harp3a.jpg)
These are the mammillary bodies on drugs:
http://docs.google.com/File?id=ajcs9hf8jc8n_47frpxq4
Any questions?
(source: The Medical Journal of Australia (http://www.mja.com.au/public/issues/jun1/harper/harper3.html) )
anterograde and retrograde amnesia
Bilateral hemorrhagic necrosis of mammillary bodies
mammillary bodies are in the hypothalamus and are part of the limbic system
irreversible
Treatment: IV Thiamine and THEN glucose