Starvation and Exercise Flashcards
What are the 4 stages of starvation?
-Post absorptive
-Early
-Intermediate
-Late
Give a brief description of what happens at each stage of starvation
-Post absorptive: depletion of free glucose and stored glycogen. Gluconeogenesis initiated
-Early: Protein catabolism to support increased gluconeogenesis. Lipolysis initiated
-Intermediate: carbohydrate and protein sparing effects of increased lipolysis, ketogenesis
-Late: fat and protein depletion
What are the 4 main metabolic priorities post prandial
-generate energy as needed in the form of ATP
-replenish glycogen
-store excess calories as triglycerides in adipose tissue
-synthesize new protein as needed
What does insulin stimulate in the fed state?
-Glucose update: GLUT4 increases
-glycogen synthesis: glycogen synthase
-fatty acid uptake and TG storage and fatty acid synthesis: LPL and acetyl CoA carboxylase
-Protein synthesis
What does insulin inhibit in the fed state?
-Glycogenolysis
-fatty acid release from TG in adipose
Why is gluconeogenesis more active in carnivores and ruminants?
Because they take in less dietary glucose
What does the liver do in the post absorptive phase?
transitions to gluconeogenesis to maintain blood glucose levels
What happens in adipose tissues during the post absorptive state?
Lipolysis initiation, HSL is activated by glucagon and catecholamines
What happens in muscle during the post absorptive state?
AA exchange, not breakdown of muscle protein. Switches to fatty acid oxidation for energy
What is the primary glucogenic amino acid in the liver?
alanine
What three molecules can muscle export to the liver for gluconeogenesis during the post absorptive state?
Pyruvate, alanine, and lactate
What are the main processes that occur during early starvation?
-hepatic gluconeogenesis
-lipolysis increases
-ketogenesis initiates in the liver
what is providing the glucogenic AA for gluconeogenesis in early starvation?
muscle protein breakdown
Why is gluconeogenesis still running in early starvation? Why doesnt the body just switch to fatty acid for energy?
the brain relies on glucose
What allows the heart to take up more fatty acids from VLDL TG in preference over adipose for use as energy during starvation?
The cardiac LPL had a 10 fold lower Km fro TG than adipose
What are the 4 main gluconeogenic substrates during early starvation?
-Lactate
-Glucogenic AA
-Glycerol
-Propionate (mainly ruminants)
What three organs transition to ketone body usage in early starvation?
muscle, heart, and kidney
Why do muscle cells inhibit pyruvate dehydrogenase in mitochondria during early starvation?
so that pyruvate can be converted to alanine to export to liver for gluconeogenesis instead of entering the TCA cycle in the myocite
Why can circulating VLDLs rise during early starvation in some species?
When the liver reesterifies some fatty acids to TG and package them for export to other tissues
What is hepatic lipidosis?
abnormal accumulation of lipid in the liver
What is the main cause of hepatic lipidosis in cats?
any disease leading to inadequate dietary intake or cellular nutrition
What is the pathophysiology of hepatic lipidosis?
anorexia leads to usage of fat stores, increases FFA and uptake by liver, increased accumulation in the liver outpaces the ability of the liver to esterify FA into TG and export as VLDL, this can lead to hepatocyte swelling and membrane damage.
What stage does the body switch to mainly fat for energy?
intermediate phase
What happens in the brain during intermediate stage?
can begin to use ketone bodies ~70%, but still needs ~30% glucose
What is the main gluconeogenic substrate during intermediate starvation? why?
glycerol, due to high fatty acid oxidation rates and protein conservation begins
What happens to the BMR during intermediate starvation?
it drops due to thyroid hormone levels dropping
What characterizes end stage starvation?
depletion of fat reserves
All protein will be catabolized in end stage starvation, what is the order of protein catabolized?
-digestive enzymes
-liver enzymes for processing food nutrients
-muscle proteins
What is refeeding syndrome?
It is when there is a sudden influx of calories and glucose which leads to insulin secretion. insulin drives movement of electrolytes from blood into cells, when electrolyte store are already low, this can lead to dangerously low levels causing hemolysis, arrhythmias, seizures, decreased cardiac output, coma.
How much does cardiac output increase during exercise?
2-5 fold
What 3 areas has increased blood flow during exercise?
coronary, skeletal muscle, and cutaneous blood flow
Explain what happens to the GI blood flow during exercise?
-initially decreased
-with increased exercise duration hypoxia can occur so there is autoregulation that can result in vasodilation when needed
What are the energy sources to skeletal muscle during sudden bursts of exercise?
-preformed ATP
-Glucose
-Creatine phosphate
