Integration of Metabolism Lecture 10

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.