Fuel Homeostasis Flashcards
Why do we need fuel homeostasis?
Sporadic intake of food, but constant requirement of energy.
CNS is entirely dependent on glucose.
Short and long term storage - mobilisation of stores.
What levels should plasma glucose be maintained between?
5 and 10 mM
What organs are involved in fuel homeostasis?
Liver - major glycogen store
Adipose - major TAG store
Muscle - majority of body mass, major consumer of fuel, some glycogen storage.
What is the absorptive state?
When ingested nutrients are entering the blood from the GI tract, approx 3 hours for an average meal.
How are proteins absorbed?
As amino acids.
How is fat absorbed?
Through lymphatics in chylomicrons (transfer fat from GI tract to adipose).
How are CHOs absorbed?
As glucose.
Explain the uptake of glucose.
Liver - net uptake, converted to glycogen for storage, alpha glycerol phosphate and fatty acids which form TAG - packaged to VDLD and transported to adipose.
Muscle - use for energy and store as glycogen.
Adipose - converted to FA and AGP - essential for TAG synthesis in adipocytes.
Explain the uptake of TAGs.
Adipocytes - chylomicron TAG releases FA, combines with AGP from glucose to form TAG in adipocytes. VLDL also releases TAG.
Other organs - oxidised to provide energy.
Explain the uptake of amino acids.
Liver - minority converted to ketoacids by deamination - TCA cycle for energy, and to FA.
Skeletal muscle and other organs - used to synthesise proteins lost by catabolism.
What is the postabsorptive state?
When the GI tract is empty and energy is supplied by the body stores.
Plasma glucose must be maintained as CNS normally only uses glucose for energy. Give 2 ways this is achieved.
Generating glucose from stored fuels - gluconeogenesis.
Glucose sparing - fat utilisation.
Glycogenolysis?
Liver and muscle - rapid but short lived response.
Hepatic genolysis is the first response.
G6P can’t be converted to glucose in muscle so undergoes glycolysis to lactate and pyruvate and circulated to the liver to produce glucose.
Lipolysis?
In adipose tissue: generates FA and glycerol - liver converts glycerol to glucose.
What happens to proteins in the postabsorptive state?
Skeletal muscle - catabolised to amino acids - converted to glucose in the liver.
After a few hours - protein becomes a major source of glucose.
