Starvation Flashcards
How much glucose do we need to provide for survival?
We need to supply the brain with 120g of glucose per day and other tissues with fatty acids. We need to conserve protein as much as possible to maintain structure and function. Glucagon is the main hormone involved and is produced by pancreas alpha cells when blood glucose drops
How is triacylglycerol stored in adipose tissue?
We have 15kg of fat stored in adipose tissue, this should be enough energy for around 40 days of starvation
Glucagon will stimulate lipolysis to release fatty acids which will be used by aerobic tissues to produce ATP except for the brain
Pathway of triacylglycerols to body
Fatty acids go out into blood in an albumin complex
Brain needs glucose, fatty acids would disrupt signals in brain
Glycerol released in blood goes into liver which can be converted into C6 molecule of glucose
How much glycogen comes from the liver?
Supply of glycerol from triacylglycerols probably only makes 20g a day and we need 120g to maintain our brains function
Liver glycogen sits at around 90-120g which can be mobilised back to glucose by glycogen phosphorylase, stimulated by glucagon leading to activation of enzyme and provides enough glucose for the brain for one day
How is glucose mobilised?
To mobilise glucose there are two enzymes involved, glycogen phosphorylase and debranching enzyme which cleaves the bond and GP comes in at the end of the chains - work together to release individual glucose molecules for metabolism
What is glycogenolysis?
Glycogen phosphorylase attaches a phosphate group onto glycogen and cleaves bond between C1 and C4 to produce glucose 1-phosphate. This is converted by mutate to glucose 6-phosphate which is metabolically active for glycolysis. In the liver, glucose-6-phosphatase traps glucose in cell (cant get across membrane) hence cleaving off phosphate and producing glucose
What is gluconeogenesis?
Occurs mainly in the liver (and kidney cortex), synthesis of glucose from lactate, alanine and glycerol, stimulated by glucagon. Fatty acid oxidation provides the energy required however cannot be used to make glucose, brain uses most of glucose
How can we supply glucose to the brain?
Glucose for brain by supply of alanine from muscle tissue, lactate from red blood cells and glycerol from break down of fatty acids. Fatty acids are used as a source of beta-oxidation for the liver, muscles and heart as well as some of the ATP which helps drive the conversion of these molecules in the liver
Glucose goes to brain and can be recycled to red blood cells for metabolism
Can protein be stored?
10-15kg of protein in body but no specific storage proteins, some protein must be degraded to amino acids to make glucose, loss of too much protein causes structural and functional damage (essentially heart and lungs may stop), protein must be conserved as much as possible
What are ketone bodies?
Ketone bodies are synthesised from acetyl-CoA in the liver from fatty acids. Acetyl-CoA can be used to make C4 molecules (ketone bodies) which are able to cross the blood brain barrier and be converted in the brain back to acetyl-CoA which can go into the CAC
Used by starving brain as an energy source
What are metabolic adaptations to starvation?
Fatty acids can be used as a fuel by all aerobic tissues (except brain), essentially unlimited supply from TAGs. Need brain to use ketone bodies and metabolise them back to acetyl-CoA to make glucose and ATP. Brain needs less glucose as a result of having ketone bodies meaning muscle degradation can slow down and the body can survive longer
