Podcast
Questions and Answers
What type of energy source does cardiac muscle primarily utilize after birth?
What type of energy source does cardiac muscle primarily utilize after birth?
What happens to muscle glycogen stores during exercise lasting 1 to 3 hours at moderately high intensity?
What happens to muscle glycogen stores during exercise lasting 1 to 3 hours at moderately high intensity?
How does the energy usage of the failing heart compare to a healthy heart?
How does the energy usage of the failing heart compare to a healthy heart?
What is the primary energy source for the brain?
What is the primary energy source for the brain?
Signup and view all the answers
Which transporters are responsible for glucose uptake in the brain?
Which transporters are responsible for glucose uptake in the brain?
Signup and view all the answers
What primarily stimulates glucose uptake by adipose tissue after a meal?
What primarily stimulates glucose uptake by adipose tissue after a meal?
Signup and view all the answers
During fasting, which hormone promotes glycogen degradation and gluconeogenesis in the liver?
During fasting, which hormone promotes glycogen degradation and gluconeogenesis in the liver?
Signup and view all the answers
Which type of muscle fiber primarily supports short-term, high-intensity exercise?
Which type of muscle fiber primarily supports short-term, high-intensity exercise?
Signup and view all the answers
What is the role of hormone-sensitive lipase during fasting?
What is the role of hormone-sensitive lipase during fasting?
Signup and view all the answers
Which substrates provide carbon skeletons for gluconeogenesis during fasting?
Which substrates provide carbon skeletons for gluconeogenesis during fasting?
Signup and view all the answers
What is the main role of acetyl-CoA in metabolism?
What is the main role of acetyl-CoA in metabolism?
Signup and view all the answers
What is the primary fuel source for resting skeletal muscle?
What is the primary fuel source for resting skeletal muscle?
Signup and view all the answers
How does insulin affect fatty acid release from adipose tissue?
How does insulin affect fatty acid release from adipose tissue?
Signup and view all the answers
Which hormone primarily responds to low blood glucose levels?
Which hormone primarily responds to low blood glucose levels?
Signup and view all the answers
What happens to slow-twitch muscle fibers in trained endurance athletes?
What happens to slow-twitch muscle fibers in trained endurance athletes?
Signup and view all the answers
What is the primary energy source that red blood cells use under normal conditions?
What is the primary energy source that red blood cells use under normal conditions?
Signup and view all the answers
What occurs during oxidative phosphorylation?
What occurs during oxidative phosphorylation?
Signup and view all the answers
During prolonged fasting, which of the following processes is stimulated by glucagon in the liver?
During prolonged fasting, which of the following processes is stimulated by glucagon in the liver?
Signup and view all the answers
Which of the following tissues is NOT a major target for insulin?
Which of the following tissues is NOT a major target for insulin?
Signup and view all the answers
What major change in fuel utilization occurs in the brain after several weeks of fasting?
What major change in fuel utilization occurs in the brain after several weeks of fasting?
Signup and view all the answers
Which process primarily occurs in the gastrointestinal tract related to carbohydrates?
Which process primarily occurs in the gastrointestinal tract related to carbohydrates?
Signup and view all the answers
What promotes triglyceride synthesis in adipose tissue after a meal?
What promotes triglyceride synthesis in adipose tissue after a meal?
Signup and view all the answers
What effect does increased levels of epinephrine have on skeletal muscle during fasting?
What effect does increased levels of epinephrine have on skeletal muscle during fasting?
Signup and view all the answers
What are the three levels at which anabolic and catabolic pathways are controlled?
What are the three levels at which anabolic and catabolic pathways are controlled?
Signup and view all the answers
Which process occurs in the liver when there is an excess of fatty acids during starvation?
Which process occurs in the liver when there is an excess of fatty acids during starvation?
Signup and view all the answers
How does prolonged fasting affect the degradation of proteins?
How does prolonged fasting affect the degradation of proteins?
Signup and view all the answers
Which energy source is utilized by the brain during both fed and fasting states?
Which energy source is utilized by the brain during both fed and fasting states?
Signup and view all the answers
What is the effect of increased insulin levels after a meal on the liver?
What is the effect of increased insulin levels after a meal on the liver?
Signup and view all the answers
Which statement is true regarding the energy source of the brain after several weeks of fasting?
Which statement is true regarding the energy source of the brain after several weeks of fasting?
Signup and view all the answers
Study Notes
Carbohydrate Metabolism
- Energy extraction from food occurs through oxidation, producing carbon dioxide and water.
- This process involves four stages.
- Stage 1: Metabolic fuels are hydrolyzed in the gastrointestinal tract.
- Stage 2: Building blocks are broken down into acetyl-CoA in tissues.
- Stage 3: The citric acid (Krebs or TCA) cycle oxidizes acetyl-CoA to CO2.
- Stage 4: Oxidative phosphorylation (using NADH and FADH2 via the electron transport chain (ETC)) produces ATP.
Metabolic Energy Storage
- ATP is created in catabolic pathways through ADP phosphorylation.
- ATP provides energy for biosynthesis (anabolic pathways).
- ATP has a limited circulation.
- Excess dietary energy is stored as fatty acids and glycogen.
- Proteins can be used for energy during prolonged fasting, but are primarily for other functions.
Regulation of Fuel Metabolism
- Insulin promotes fuel storage (anabolic hormone).
- Glucagon, epinephrine, cortisol, and growth hormone oppose insulin's action.
- Glucagon responds to low blood glucose by promoting glucose release into the blood.
- Anabolic and catabolic pathways are controlled by:
- Allosteric inhibitors and activators of rate-limiting enzymes.
- Control of gene expression by insulin and glucagon.
- Phosphorylation (glucagon) and dephosphorylation (insulin) of rate-limiting enzymes.
Well-Fed State
- Immediately after eating, blood glucose increases, triggering insulin release.
- Insulin promotes glycogen synthesis in the liver and muscles.
- Excess glucose is converted into fatty acids and triglycerides.
- Insulin promotes triglyceride synthesis in adipose tissues and increases protein synthesis in muscle.
- Most energy needs of the liver come from amino acid oxidation.
- The brain and red blood cells don't need insulin to use glucose.
Post-Absorptive State
- During an overnight fast, glucagon and epinephrine levels increase.
- These hormones stimulate glycogen degradation and glucose release in the liver.
- Hepatic gluconeogenesis is stimulated, but slower than glycogenolysis.
- The decrease in insulin combined with increased epinephrine stimulates the release of amino acids from muscle tissue and fatty acids from adipose tissue.
- Amino acids and fatty acids are taken up by the liver.
- Fatty acid oxidation provides ATP for gluconeogenesis.
Starvation/Prolonged Fast
- Glucagon and epinephrine levels are significantly high during starvation.
- Lipolysis occurs rapidly, generating excess acetyl-CoA for ketone synthesis.
- Muscle tissue relies mainly on fatty acids as its fuel.
- The brain adapts to use ketones for energy; approximately two-thirds during prolonged fast.
- Shifting to ketone use reduces the amount of protein needed for gluconeogenesis.
- Red blood cells and renal medulla depend entirely on glucose.
Patterns of Fuel Metabolism in Tissues
- Different organs utilize various fuels depending on whether the body is well-fed or fasting.
- Liver: glucose and amino acids (well-fed), fatty acids (fasting).
- Resting skeletal muscle: glucose (well-fed), fatty acids and ketones (fasting).
- Cardiac muscle: fatty acids (well-fed, fasting).
- Adipose tissue: glucose (well-fed), fatty acids (fasting).
- Brain: glucose (well-fed), glucose and ketones (fasting).
- Red blood cells: glucose (well-fed, fasting).
Liver
- Maintains constant blood glucose levels.
- Synthesizes ketones when excess fatty acids are oxidized.
- After a meal, the liver replenishes glycogen stores using glucose from the portal blood.
- Excess glucose is converted to acetyl-CoA and used for fatty acid synthesis.
- The liver prioritizes using excess amino acids for energy during a well-fed state.
- During fasting, the liver releases glucose into the blood and promotes gluconeogenesis using lactate, glycerol, and amino acids as carbon skeletons.
Adipose Tissue
- Insulin stimulates glucose uptake and fatty acid synthesis in adipose tissue.
- Lipoprotein lipase, an enzyme induced by insulin, breaks down triglycerides.
- Insulin inhibits fatty acid release.
- During a fast, decreased insulin and elevated epinephrine activate hormone-sensitive lipase, which releases fatty acids.
- Adipose tissue stores fatty acids as triglycerides.
Skeletal Muscle
- Skeletal muscle uses glucose and fatty acids as primary fuels.
- After a meal, muscle takes up glucose and amino acids to replenish glycogen and protein stores.
- During fasting, muscle primarily uses fatty acids.
- Ketones can be used if the fasting state is prolonged.
Active Muscle
- The primary fuel for active muscle depends on the intensity and duration of the exercise.
- Fast-twitch fibers rely on anaerobic glycolysis for short-term, high-intensity exercise.
- Slow-twitch fibers use more oxidative pathways for sustained exercise, oxidizing both glucose and fatty acids.
- Muscle glycogen stores are depleted after a few hours of continuous exercise at moderate intensity.
Cardiac Muscle
- Fetal cardiac muscle primarily uses glucose for energy.
- Postnatally, cardiac muscle shifts to fatty acid ß-oxidation.
- Ketones are used during prolonged fasts.
- Cardiac muscle closely resembles skeletal muscle during prolonged exercise.
- In patients with cardiac hypertrophy, the situation reverses partially.
- In failing hearts, glucose oxidation rises while β-oxidation decreases.
Brain
- The brain uses 20% of total oxygen and 25% of total glucose.
- Blood glucose concentration is tightly regulated to supply the brain with glucose.
- The brain uses glucose primarily as fuel; ketones are an alternative energy source during prolonged fasting, providing about two-thirds of the fuel needed.
- Red blood cells cannot use ketones and rely solely on glucose.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
This quiz covers the key stages of carbohydrate metabolism and the regulation of fuel metabolism in the body. Learn about the processes from energy extraction to ATP generation, including the roles of hormones like insulin and glucagon. Test your knowledge on how the body stores and uses energy from food.
