30 Questions
What happens to the constituent parts of carbohydrates, fats, and proteins after digestion?
They are transported across the intestinal wall and enter the bloodstream or lymphatic system
What is the primary reason why our body needs to store energy?
To meet the constant demand for energy from organs like the brain
What is the name of the state that occurs after a meal when the body is digesting and absorbing nutrients?
Absorptive state
During the absorptive state, what happens to anabolism and catabolism?
Anabolism exceeds catabolism
Where does the digestion of carbohydrates begin?
In the mouth
What would happen if there were no method in place to store excess energy?
We would need to eat constantly
Where are the absorbed nutrients transported to from the intestines?
Liver, adipose tissue, or muscle cells
What stimulates the release of insulin into the bloodstream?
The ingestion of food and the rise of glucose concentrations in the bloodstream
What is glucose immediately converted into once inside the liver, adipose, and muscle cells?
Glucose-6-phosphate
What is the purpose of the concentration gradient established by the conversion of glucose into glucose-6-phosphate?
To allow glucose to continue moving from the blood to the cells
What is the role of insulin in muscle cells?
To promote the synthesis of protein
What happens to the dietary fats and sugars ingested shortly after eating?
They are processed and used immediately for energy
What happens when the carbon sources for gluconeogenesis are depleted?
Proteins from muscles are released and broken down for glucose synthesis
What is the universal currency of energy in the cell?
ATP
What is the purpose of integrating metabolism?
To ensure a supply of energy for all tissues at all times
What is the result of a positive caloric balance?
A significant proportion of food energy intake is stored as either glycogen or fat
What is the function of NADPH in metabolism?
Reductive biosynthesis
What is the common intermediate in the metabolism of macromolecules?
acetyl CoA
What is the first priority for survival when the body is deprived of nourishment for an extended period of time?
Provide enough glucose or fuel for the brain
Which of the following is NOT used as a source for gluconeogenesis during starvation?
Fatty acids from adipose tissue
What is the primary source of fuel for the heart and other organs after several days of starvation?
Ketone bodies
What process is shut off in cells that can use alternative fuels during starvation?
Glycolysis
What is the fate of pyruvate, lactate, and alanine from muscle cells during starvation?
They are used to synthesize glucose in the liver
What is the primary role of ketones during starvation?
To provide energy for the brain and other glucose-dependent organs
What is the primary fuel source for the heart muscle?
Fatty acids
What happens to pyruvate in skeletal muscle cells?
It is converted to lactate and alanine
What is the function of hormone-sensitive lipase in adipose tissue?
To break down triacylglycerol
What is the brain's primary fuel source under normal conditions?
Glucose
What is unique about heart muscle metabolism compared to skeletal muscle?
It can only function under aerobic conditions
What is the brain's adaptation during fasting conditions?
It adapts to use ketone bodies as fuel
Study Notes
Absorptive State
- The absorptive state occurs after a meal when the body is digesting food and absorbing nutrients.
- During this state, anabolism exceeds catabolism, and the body stores energy for later demands.
- The digestion of carbohydrates begins in the mouth, while the digestion of proteins and fats begins in the stomach and small intestine.
Insulin and Glucose Absorption
- Insulin is released by pancreatic beta cells in response to increased glucose concentrations in the bloodstream.
- Insulin initiates the absorption of blood glucose by liver hepatocytes, adipose, and muscle cells.
- Glucose is converted into glucose-6-phosphate inside these cells, establishing a concentration gradient that allows glucose to continue moving from the blood to the cells.
Energy Storage and Use
- If energy is needed shortly after eating, dietary fats and sugars are processed and used immediately for energy.
- This prevents the continued breakdown of proteins that serve as carbon sources for gluconeogenesis.
- Once these stores are fully depleted, proteins from muscles are released and broken down for glucose synthesis.
- Overall survival is dependent on the amount of fat and protein stored in the body.
Integration of Metabolism
- The integration of metabolism refers to the co-ordination of the three metabolites (carbohydrates, lipids, and proteins).
- Its significance lies in ensuring a supply of suitable energy for all tissues at all times.
- ATP is the universal currency of energy, generated by the oxidation of glucose, fatty acids, and amino acids.
Starvation
- When the body is deprived of nourishment for an extended period, it goes into “survival mode.”
- The first priority is to provide enough glucose or fuel for the brain.
- The second priority is the conservation of amino acids for proteins.
- The body uses ketones to satisfy the energy needs of the brain and other glucose-dependent organs.
Tissue-Specific Metabolism
- Adipose tissue stores triacylglycerol, which is continuously synthesized and broken down, controlled by hormonal sensitive lipase.
- Glucose is needed to synthesize triacylglycerol, and glucose levels determine if fatty acids are released into the blood.
- Heart muscle metabolism is different from skeletal muscle in three ways: it can only function under aerobic conditions, it cannot store glycogen, and fatty acids are the preferred fuel.
- Brain metabolism is characterized by a very high respiratory rate, and it normally uses glucose as its sole preferred fuel.
Learn about the integrated metabolism of carbohydrates, proteins, and fats, and how the body meets its constant demand for energy through storage and processing of food.
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