AAMC FL1 BB #55

[663697]

The TPR book says that ketone bodies can cross the blood-brain barrier and then be converted back into acetyl-CoA to enter the Krebs cycle to produce energy. Despite using this info to answer the question, I got it wrong. I'm not sure why utilizing fatty acids for energy would be incorrect.

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[Nugester]

For this one, remember that the brain always wants glucose. It doesn't want anything else! Yes, it can use ketones in a metabolic crisis, however, if there is any glucose around, it will still take it over a high abundance of ketones. And because there is a high preference for glucose as the primary substrate, it wouldn't make sense for it to wait for insulin-dependent transporters to kick in. So "B" is the best answer.

 

[663697]

For this one, remember that the brain always wants glucose. It doesn't want anything else! Yes, it can use ketones in a metabolic crisis, however, if there is any glucose around, it will still take it over a high abundance of ketones. And because there is a high preference for glucose as the primary substrate, it wouldn't make sense for it to wait for insulin-dependent transporters to kick in. So "B" is the best answer.

If they have insulin-independent transporters, what would qualify as a metabolic crisis? Such as if those transporters aren't working, and there is no other alternative but to transport ketone bodies?

 

[Nugester]

Like extreme starvation; if you have no glucose around you'll start producing ketone bodies for energy. Brain has no time for that though. It is a high energy organ that needs it fast.

 

[PaulTownMD]

As already stated, the brain has a high demand for energy and utilizes GLUT 1 (insulin-independent transporters found in BBB endothelial tissue), which helps protect brain glucose uptake from hormonal fluctuations. During diabetic ketoacidosis (from body's inability to uptake and metabolize glucose), solute imbalances can cause cerebral edema and disrupt healthy transport across the BBB