Integrated Metabolism Flashcards
What are the primary ingested and absorbed macronutrients during the fed state (3 hours after a meal)?
Glucose, fatty acids, and amino acids, depending on food intake.
Describe the postabsorptive or early fasting state (3 – 18 hours).
Sources of fuel shift from ingested glucose, amino acids, and fatty acids to liver glycogenolysis, providing glucose released into the blood and delivered to tissues.
What characterizes the fasting state (18 hours – 2 days without food intake)?
Glycogen stores are depleted, and de novo glucose formation occurs in the liver using precursors such as amino acids, glycerol, and lactate.
Explain the key pathways in the postabsorptive state.
After the initial phase of liver glycogenolysis, gluconeogenesis becomes vital, utilizing precursors like lactate and the glucose-alanine cycle. Muscle glycogenolysis provides glucose for muscles, and lipolysis releases fatty acids.
What happens to liver and muscle glycogen stores after an overnight fast, and what remains the main fuel source?
Liver and muscle glycogen stores are depleted, and glucose remains the main fuel source through glycolysis or gluconeogenesis.
Outline the key pathways in the fasting state (18 – 48 hours of no food intake).
Glycogen stores are depleted, and de novo glucose formation occurs in the liver using precursors such as amino acids, glycerol, and lactate. Increased glucagon secretion stimulates lipolysis, leading to fatty acids as an energy source.
How does the body utilize proteins during the fasting state, and what is the role of glucagon?
Amino acids from muscle protein breakdown contribute to de novo glucose formation, stimulated by increased glucagon secretion, leading to large losses of nitrogen through urine.
What are the key pathways during starvation (long-term fast)?
A metabolic shift spares body proteins, relying on gluconeogenesis and lipolysis. Plasma fatty acids become a major fuel for the heart, liver, and skeletal muscle, leading to the formation of ketones for brain energy.
Explain the role of glycerol during starvation and the organ responsible for gluconeogenesis after several weeks.
Glycerol from lipolysis serves as a precursor for gluconeogenesis, and the kidney becomes the organ for gluconeogenesis after several weeks.
Describe the key pathways during continued starvation and the role of TCA cycle intermediates.
Continued starvation leads to the depletion of TCA cycle intermediates for gluconeogenesis, with an accumulation of acetyl-CoA from fatty acid degradation. This results in increased ketone body formation in the liver.
What happens to ketone bodies in the blood during continued starvation, and how are they utilized in the body?
Ketone bodies in the blood increase, leading to ketosis. They serve as a source of fuel in skeletal muscle, heart, and brain, sparing amino acids for essential proteins.
How does the duration of starvation vary based on body fat levels?
3 months for adults with normal weight and body fat, and 1 year for obese adults, with potential physiological damage due to ketosis.
What occurs after the depletion of fat reserves during prolonged starvation?
Essential proteins are used to form glucose, leading to the loss of liver and muscle function.
Explain the fuel use by the brain during starvation.
The brain switches from relying on glucose to ketones as a source of fuel during starvation.
Describe the fuel metabolization during starvation, focusing on reliance on adipose tissue lipolysis.
During starvation, there is a higher reliance on adipose tissue lipolysis, leading to increased muscle protein degradation.
