Basic science Flashcards
What second line tests are available for patients with suspected b12 deficiency who have borerline holocobalamin (active b12) and/or borderline total b12 levels?
MMA and homocysteine.
-MMA (methylmalonic acid) is a substrate present primarily in mitochondria that accumulates in the absence of B12. An MMA precursor (methylmalonyl-CoA) with be preferentially converted to succinyl-CoA in the presence of B12 - a critical intemediary in the TCA cycle - but converted to MMA when there isn’t sufficient B12.
-homocysteine is a component of the methionine cycle. It is processed in the presence of B12 by methionine synthase to methionine, and simultaneoulsy methionine synthase in the presence of B12 and homocysteine conversts methyl-H4-hydrofolate (dietary folate) to H4-hydrofolate which participates in thymidine synthesis. All these components are necessary for the reaction. In the absence of b12, or dietary folate, or vitamine B6, homocysteine accumulates and can be measured.
What is the nucleotide that depends most on B12 and folate?
Thymidine (aka thymine) (T). Folate processing (or the folate cycle), which is B12 dependent, is necessary to make folate into an available form for thymidine synthesis.
What is the predominant lactate isomer in humans?
L-lactate, derived from pyruvate during anaerobic respiration. D-lactate is less prevalent and comes from instestinal flora.
What are type A and type B lactic acidosis?
Type A - excess lactic acid production. Type B - impaired hepatic metabolism of lactate.
What is the relationship between vascular resistance and vessel diameter?
4th power rule. Resistance = inverse radius to 4th power.
What vessel typically supplise the SA node?
RCA in 60% of patietns. LCA in the rest.
What vessel typically supplies the AV node?
RCA in 90% of patients. Left circumflex in about 10%.
Whate vessel typically supplies the the bundle of His?
Right coronary artery, with minor contribution from the septal perforators off the LAD.
What vessel typically supplies the left bundle branch?
Left anterior descending. RCA and LCx make minor contributions.
What vessel typically supplies the right bundle branch?
Septal perforators from the LAD. Minor collatoral may be supplied from the RCA (if RCA dominant) or the LCA (if LCA dominant).
What happens to catecholamine sensitivity during metabolic acidosis?
Reduced. Increased pressor requirements etc.
What is the formula for BMI?
Weight in kgs/Height in metres squared
