Why brain cell use only glucose???

In the case of red blood cells: human erythrocytes, have no mitochondria. Since the mitochondria are the cellular site for oxidative metabolism of fatty acids, erythrocytes cannot oxidise fatty acids to release energy. The erythrocytes also cannot fully oxidise glucose (to carbon dioxide and water) because this is also a mitochondrial process, so they have to rely upon anaerobic glycolysis. The end product of anaerobic glycolysis is pyruvate, and erythrocytes reduce this to lactate (to recycle the NADH that is produced during glycolysis) and then export this lactate into the blood for further metabolism by the liver. This way they can still obtain some ATP for cellular processes.

Hope that helps , i'm guessing for neurons its a similar reason (but i'm not sure about that part)

In the case of red blood cells: human erythrocytes, have no mitochondria. Since the mitochondria are the cellular site for oxidative metabolism of fatty acids, erythrocytes cannot oxidise fatty acids to release energy. The erythrocytes also cannot fully oxidise glucose (to carbon dioxide and water) because this is also a mitochondrial process, so they have to rely upon anaerobic glycolysis. The end product of anaerobic glycolysis is pyruvate, and erythrocytes reduce this to lactate (to recycle the NADH that is produced during glycolysis) and then export this lactate into the blood for further metabolism by the liver. This way they can still obtain some ATP for cellular processes.

Hope that helps , i'm guessing for neurons its a similar reason (but i'm not sure about that part)

Im pretty certain neurones do have mitochondria, nerve impulses require a large amount of energy!

I read around the interwebs, and it seems technically brain cells can respire other things (like ketoacids), but I doubt this will be looked upon at A2.

Neuron's do indeed have mitochondria. Aside from glucose they can use ketones (ketone bodies) which are produced in the body where there is a lack of glucose. In theory they could use FFAs but they do not cross the blood-brain barrier very easily as they are normally bound to plasma proteins.

RBCs need glucose only as they have no mitochondria, the reasons being explained above. All cells need glucose for normal metabolic processes such as cell repair etc.

Ya I know they use ketoacids.
I wasn't sure why they don't use anything other than glucose coz that will mean they don't have mitochondria bt neurones they do have mitochondria. I think its because my book just wrote glucose I got confused. They use ketoacid only when there is not enough glucose right? If they use keto acid then they do have mitochondria.
Thanks a lot!

No, it's nothing to do with mitochondria when it comes to the brain - simply that free fatty acids cannot physically get from the blood into the brain cells because they are too big to pass through the very selective blood brain barrier. Hence, the only available energy source is either glucose or ketones.

Brain cells (neurones) DO have mitochondria and plenty of them.

Yes, ketones are produced during starvation (low glucose) by the liver. Ketones can pass through the blood brain barrier and enter neurones to be used as energy.

Hope that makes sense.

I've always wondered why!

simply that free fatty acids cannot physically get from the blood into the brain cells because they are too big to pass through the very selective blood brain barrier.

I have really a lot of qsns.
My textbook says RBC and brain cells use only glucose.
But RBC doesn't have mitochondria what does it use glucose for?
Does brain cells have mitochondria I know cell body of neurone does. I also know that brain cells use ketone as well.
What I don't understand is why both cells use only glucose or ketone even though they dont have mitochondria.

Why have you been negged? It's quite a good question, and what do brain cells use ketone for?

Ikr!
they use ketone when there is few glucose available

Okay, thanks! (: