Muscles at rest metabolism

[deleted783484]

1. Why do skeletal muscles use fats and ketone bodies when fasting? Can they not do glycogenolysis to use glucose for energy?

The kaplan book says that skeletal muscles use glucose as a source of energy after a meal but they use fats and ketone bodies when fasting. can they not use glucose when fasting from the glycogen stored?

2. Why does the heart use fatty acid as the primary source and not glucose?

Thanks a lot! x

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[yeasureyoubetcha]

1. Why do skeletal muscles use fats and ketone bodies when fasting? Can they not do glycogenolysis to use glucose for energy?

They will initially do glycogenolysis until the glycogen stores are depleted. Skeletal muscles is very happy using fats and ketone bodies for energy actually when fasting. It helps buffer the blood glucose supply reserving glucose for the brain and RBCs.

The kaplan book says that skeletal muscles use glucose as a source of energy after a meal but they use fats and ketone bodies when fasting. can they not use glucose when fasting from the glycogen stored?

Energy utilization
Fed: Dietary glucose
Early fasting: Whatever glucose is left + Liver glycogenolysis
Late fasting: Liver glycogenolysis + GNG ramping up (takes 10hrs to activate the pathways completely)
Early starvation: (+24hrs): GNG utilizing muscle AA's + GNG utilizing FA
Full starvation: GNG utilizing Fats until fat reserves depleted then liberates whatever muscle is left for AA sources-->death

2. Why does the heart use fatty acid as the primary source and not glucose?
Thanks a lot! x

It uses both. Fat is the best source of energy though. There's always some around and you get a lot of energy out of it. Cardiac muscle isnt as great as storing glycogen. Cardiac muscle is always being used so there's no real time for it to rest and make glycogen. If it did that we'd die.

 

[deleted783484]

They will initially do glycogenolysis until the glycogen stores are depleted. Skeletal muscles is very happy using fats and ketone bodies for energy actually when fasting. It helps buffer the blood glucose supply reserving glucose for the brain and RBCs.



Energy utilization
Fed: Dietary glucose
Early fasting: Whatever glucose is left + Liver glycogenolysis
Late fasting: Liver glycogenolysis + GNG ramping up (takes 10hrs to activate the pathways completely)
Early starvation: (+24hrs): GNG utilizing muscle AA's + GNG utilizing FA
Full starvation: GNG utilizing Fats until fat reserves depleted then liberates whatever muscle is left for AA sources-->death


It uses both. Fat is the best source of energy though. There's always some around and you get a lot of energy out of it. Cardiac muscle isnt as great as storing glycogen. Cardiac muscle is always being used so there's no real time for it to rest and make glycogen. If it did that we'd die.

amazing answer! THANK YOU!!