Control of metabolism Flashcards
What is metabolism?
Extract energy from nutrients
Use energy for work and synthesis
Store excess energy
Two pathways
- Anabolic –> build large molecules
- Catabolic –> break down large molecules
Two states
- Absorptive –> ‘fed’ - anabolic
- Post-absorptive –> ‘fasted’ - catabolic
What are the energy stores?
Glycogen store: –> 600g maximum
- Liver
- Muscle
Adipose:
- No limit of fat that can be stored
What is the oral glucose tolerance test?
Glucose drink containing 75g
- measures the amount of glucose being absorbed
- monitors glucose levels in the blood over the next two hours
In comparison to the placebo group (orange squash), there is a larger peak of blood glucose, placebo remains quite constant, similar to that of fasting conditions. Decrease after peak following insulin release from pancreatic beta cells.
How does the liver produce glucose?
Glyconeolysis –> breakdown of glycogen stores
- Glucose-6-phosphate –> either continue to pyruvate or becomes glycogen
Gluconeogenesis –> glucose synthesised from non-carbohydrate precursors in the liver
Availability of glucose in liver and muscle cells determines which of these enzymes is activated or inhibited
What is gluconeogensis?
Formation of glucose in the liver from non-carbohydrate precursors.
- main precursors are lactate, glycerol, alanine, and glutamine
- requires energy
- activation of enzymes in these processes is determined by levels of glucose and pyruvate and enzymes controlling them
Lactate produced in anaerobic respiration
How is fat metabolised?
- Body fat is stored mostly in adipocytes and triglycerides. Clusters of adipocytes form adipose tissue
- Release of fatty acids and glycerol into bloodstream allow energy production
- 2.5x more ATP from fat than CHO
- Excess glucose can readily be converted and stored as fat
- Breakdown is known as lipolysis
- Low glucose stores/ levels activate lipolysis. Glycerol converted into glucose
Fatty acids can be used to for some keto-acids used to form some amino acids
What controls metabolism?
The ratio of insulin and glucagon
Glucose levels alters the ration
What happens when insulin levels are higher in the ratio?
Anabolic state
Absorptive state
- Increase glucose oxidation
- Increase glycogen synthesis
- Increase fat synthesis
- Increase protein synthesis
What happens when glucagon levels are higher in the ratio?
Catabolic state
Post-absorptive state
Fasted - low glucose levels
- Increase glycogenolysis
- Increase gluconeogenesis
- Increase ketogenesis
What occurs in the post-absorptive state?
e.g before breakfast
Glucagon increases
Blood glucose fairly constant at 5mmol/min
Blood glucose maintained by
- glycogenolysis
- gluconeogenesis
50:50 balance between processes
Glucagon mechanism
Low blood glucose levels –> alpha cells from pancreas release glucagon –> signals liver to break glycogen into glucose –> bring glucose levels back to homeostasis
Insulin levels low –> uptake of glucose to adipose and muscle is low
Glucagon effects in liver
- Glycogenolysis
- Gluconeogenesis
- Synthesis of ketones
What is the effect of glucagon on carbohydrate and fat metabolism?
Stimulates lipolysis to use fat as fuel
Stimulates gluconeogenesis in the liver
Inhibits glycogen synthesis
Promotes the conversion of fatty acids to ketone bodies in the liver –> enough energy for brain, can use glucose and ketones
What happens to fat metabolism in the post-absorptive phase?
Low insulin sends signals that energy must be made from triglycerides –> FA and glycerol
Brain:
- Glucose oxidation
Muscle:
- Low insulin prevents glucose uptake from plasma
- HIgh levels of plasma FFA
- FA taken up by liver and muscle and enter mitochondria for oxidation
Minimum energy from glucose will go to the brain
Hydrolysis of triglycerides into FFA release in the bloodstream
- HSL (hormone-sensitive lipase) stimulated by glucagon/ low insulin
- Activate triglyceride breakdown into glycerol and fatty acids
- Glycerol to the liver to produce energy
- FFA released into the blood –> can be converted to ketone bodies to supply energy to the brain
How do ketones provide the brain with energy?
From lipolysis –> FFA undergo beta oxidation –> become AcetylCoA –> enter krebs cycle
-> in liverAcetylCoA converted to Ketones –> energy for the brain
What occurs in the absorptive phase?
Anabolic state
- Suppression of mobilisation of endogenous fuels
- Production of glucose by the liver is inhibited
- FFA release from adipose is inhibited
- Body preserves its stores
- Starts to use incoming fuels and stores excess
Insulin excretion after feeding is caused by:
- secretion of secretin and CCK from duodenum in response to food
- rise in plasma glucose and amino acids following the absorption of digested food
GLUT4 carrier made present in muscle and adipose tissue, activity influenced by insulin
- in basal conditions, found in membrane and cytosol
- insulin increases the movement of GLUT4 translocation by 10-20x
What are some consequences of increased insulin?
- Increased uptake and utilisation of glucose by cells
- Increased storage of glucose as glycogen
- Increased amino acid uptake and protein synthesis –> stimulates enzymes involved in protein synthesis, inhibits those involved in protein catabolism
- Increased uptake and storage of fat by adipose tissue
