Fuel homeostasis Flashcards
why do we need fuel homeostasis
we have a constant requirement of nutrients for tissues, but sporadic food intakes
What metabolic substrate does the CNS rely on
glucose, other nutrients cannot cross the BBB
What blood plasma [glucose] is needed to stay alive
above 5mM. Glucose homeostasis ensures blood plasma glucose remains between 5 and 10mM
which organs are involved in fuel homeostasis?
Liver = major glycogen store short term & turns nearly every nutrient into glucose Adipose = major TAG store, long term Muscle = major consumer of fuel, with a short term glycogen store for its own use
What is the absorptive state
when ingested nutrients are enterng the blood from the GI tract; ~3 hrs after a meal
what happens to glucose in absorptive state
- net uptake in the live, converted to glycogen and excess as alpha GP for TAG
muscles use glucose for energy and store some as glycogen
what happens to FA in the absorptive state
in adipose FA form TAG for storage
in other organs some ingested fat is oxidesed for energy
what happens to amino acids in the absorptive state
liver: minority converted to keto aids by deamination to enter TCA cycle
skeletal muscle & other organs: use AA to synthesise proteins and replace proteins lost through catabolism
what is the post-absorptive state
when the GI tract is empty and energy is supplied by the body stores. this is the default mechanism; catabolism of stored energy
what is the default body state?
post-absorptive. Catabolism of stored energy
how is glucose levels maintained for CNS function
- generation of glucose from stored fuels = gluconeogenesis
- glucose sparing, by utiliasation of FA and AA
gluconeogenesis
generation of glucose from stored fuels
fastest, most efficient way to produce glucose from stored fuels in PA state
glycogenolysis
key characteristics of glycogenolysis
rapid
short lived
what is the first repsonse to maintainng plasma glucose levels?
hepatic glycogenolysis
is glucose-6-phosphate converted to glucose in the muscle?
no this cannot occur. instead G6P undergoes glycolysis to produce lactate and pyruvate which circulate the liver and are coverted to glucose
how does muscle make glucose from G6P
occurs indirectly. G6P undergoes glycolysis to produce lactate and pyruvate which circulate the liver and are coverted to glucose
lipolysis
Adipose generates FA and glycerol from TAG
liver converts glycerol to glucose
glycogenolysis from protein
AA converted to glucose in the liver
short term; only 5-10% catabolised
what is the major source of glucose after a few hours in the PA state?
protein
glucose sparing
fat is utilised to spare glucose for CNS.
Organs will reduced glucose utilisation and instead oxidise FA to produce acetyla CoA to encer TCA cyle
fatty acid oxidation
produces acetyl co-a to entre TCA cycle
what state will the body enter in prolonged starvation
ketosis. In the liver, acetyl coA from FA oxidation will be converted to ketones and relesed in the blood for fuel by tissues. In extended starvation, body enters ketosis
two main control systems for maintaining A and PA states
endocrine & neural control
