30 Questions
Which hormone inhibits fatty acid synthesis by diminishing the production of pyruvate?
Glucagon
During the early fasting stage, what does glucagon promote the release of by adipose tissue?
Fatty acids
What happens to the liver during the refeeding stage after breakfast?
Remains in a gluconeogenic mode
Which metabolic process is responsible for converting glucose into ATP in anaerobic conditions?
Glycolysis
What is the main target organ for glucagon in the body?
Liver
Which process results in the shift of fuel from glucose to fatty acids by muscle and liver?
Beta oxidation
What is the reason that β-oxidation of fatty acids by muscle halts the conversion of pyruvate into acetyl CoA?
Acetyl CoA inhibits the phosphorylation of pyruvate dehydrogenase complex.
During days 1-3 of starvation, what is a significant raw material for glucose synthesis in the liver?
Glycerol
Which compound must be converted to Ketone Bodies on days 3-7 of starvation due to its inability to leave liver cells?
Acetyl CoA
What is the primary reason for the liver to produce large amounts of Ketone Bodies during extended starvation?
Limiting levels of oxaloacetate
Which compound is considered a "portable" form of Acetyl CoA, mainly produced in the liver's mitochondria?
D-3-hydroxybutyrate
In the context of energy generation during starvation, which molecules contribute to the production of Acetyl CoA?
Amino acids and fatty acids
What are the primary fuels for heart and skeletal muscle during starvation?
Ketone bodies
Which organ uses lactate for fuel during a period of 1-3 days of starvation?
Brain
What process becomes the primary source of glucose during the 1-3 days of starvation?
Heptic gluconeogenesis
Which fuel becomes the primary source for the brain after 3-7 days of starvation?
Ketone bodies
What leads to death during starvation?
Depletion of energy stores leading to loss of function of heart, liver, kidney
Which event is an example of studying the effects of intrauterine deprivation and subsequent adult health?
Dutch famine Nov 1944 - Apr 1945
What is the primary role of gluconeogenesis during starvation?
To provide sufficient glucose to the brain and other tissues
What happens to the fuel used by muscle during starvation?
It shifts from glucose to fatty acids
What is the normal glucose concentration that the human body attempts to maintain?
4-6 mmol/L
What is the result of the action of pyruvate carboxylase and PEP carboxykinase in gluconeogenesis?
Formation of phosphoenolpyruvate (PEP) from pyruvate
Why can't fatty acids be converted into glucose?
Because acetyl CoA cannot be transformed into pyruvate
What is the role of pancreatic islets of Langherhans in glucose homeostasis?
Secrete glucagon and insulin
What is the primary source of energy during prolonged starvation?
Fatty acids from triacylglycerols
During periods of fasting, what happens to the release of fatty acids?
Increases
What is the enzyme responsible for converting fructose 1,6-bisphosphate to fructose 6-phosphate?
Fructose 1,6-bisphosphatase
What is the process by which glucose is synthesized from non-carbohydrate sources during fasting?
Gluconeogenesis
What is the primary source of energy for the liver and muscle during periods of fasting?
Fatty acids
What is the process by which glucose is converted into energy in the presence of oxygen?
Aerobic respiration
Study Notes
Cellular Metabolism
- Cellular metabolism involves converting energy from food into cellular energy (ATP)
- Processes involved: beta oxidation, glycolysis, anaerobic oxidative deamination, and electron transport and oxidative phosphorylation
Fat and Glucose Metabolism
- Glucagon increases lipolysis and inhibits fat synthesis
- Fat is stored in adipose tissue and released as fatty acids during fasting
- Glucose is stored in the liver and muscles as glycogen, and released during fasting
Stages of Fasting
- Post-absorptive stage: after a meal, glucose and amino acids are transported to the blood, and lipids are packed into chylomicrons and transported to the blood via the lymphatic system
- Early fasting stage: during the night, glucagon levels increase, and glucose and insulin levels decrease, leading to glycogen breakdown and fatty acid release
- Refed stage: after breakfast, the liver remains in a gluconeogenic mode, and newly synthesized glucose is used to replenish liver glycogen stores
Glucose Metabolism During Starvation
- Days 1-3: glucose is synthesized from alanine, lactate, and pyruvate through gluconeogenesis in the liver
- Days 3-7: acetyl-CoA is converted to ketone bodies (acetoacetate, d-3-hydroxybutyrate, and acetone) in the liver, which are then used as fuel by the heart, skeletal muscle, and other organs
Fuel Choice During Starvation
- Plasma levels of fatty acids and ketone bodies increase, while glucose levels decrease
- Fuel choices during starvation:
- 24h: glycogen
- 1-3d: hepatic gluconeogenesis
- 3-7d: free fatty acids and ketone bodies
- 1W+: protein
Starvation in Humans
- Examples of starvation studies: Dutch famine, Minnesota starvation study, Irish hunger strike, and the siege of Leningrad
- Effects of starvation on the human body: depletion of energy stores, protein degradation, and changes in carbohydrate, fat, and protein metabolism
Ketone Bodies
- Ketone bodies are produced in the liver during starvation and are used as fuel by the heart, skeletal muscle, and other organs
- Acetoacetate, d-3-hydroxybutyrate, and acetone are the three ketone bodies produced
- Ketone bodies are "portable" forms of acetyl-CoA that can be used by other organs for energy production
Barker Hypothesis
- The Barker hypothesis states that intrauterine undernutrition can lead to changes in glucose metabolism and increase the risk of adult-onset diseases, such as diabetes and cardiovascular disease
Test your knowledge on cellular metabolism processes including fat synthesis, glucose uptake, glycolysis, Krebs cycle, and ATP production. Understand how energy is converted from food to cellular energy through various metabolic pathways.
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