Macronutrient Metabolism and Absorption

Macronutrient Metabolism

• Ingested proteins, fats, and carbohydrates break down through digestion.
• Digestion starts with chewing to reduce food into smaller portions.
• Initial digestion takes place in the stomach.
• The intestines continue the digestion processes.
• Proteins break down into amino acids.
• Fats (triglycerides) break down into glycerol and fatty acids.
• Carbohydrates (sugars) break down predominantly into glucose.
• Absorption occurs once these components break down.

Nutrient Absorption

• Amino acids, glucose, glycerol, and fatty acids absorb into the portal vein.
• The portal vein carries nutrients directly to the liver from the intestines for processing.
• Unlike other nutrients, triglycerides (as glycerol and fatty acids) absorb into the lymphatic system.
• The lymphatic system transports triglycerides into the systemic circulation, which is the bloodstream going to the entire body.
• Fats are delivered throughout the entire body before the liver.

Liver Processing and Storage

• The liver processes the absorbed nutrients.
• The body stores the products after a meal.
• Amino acids are stored as proteins.
• Glucose is stored as glycogen.
• Glycerol and fatty acids are stored as triglycerides (fat).
• Biological terms that are stored and inactive end in "ogen".

Energy Production (ATP)

• The body uses stored substances in order to produce energy (ATP).
• Glucose serves as the primary energy source.
• Glucose converts into pyruvate.
• Pyruvate enters the mitochondria and transforms into acetyl-CoA.
• Acetyl-CoA proceeds through the Krebs cycle (citric acid cycle).
• Carbon dioxide (waste) and ATP (energy) are released.
• Glucose converts into pyruvate and creates a small amount of ATP.
• Acetyl-CoA releases hydrogen during the Krebs cycle.
• Hydrogen moves to the membrane of the mitochondria.
• Hydrogen interacts with transmembrane proteins and oxygen in the mitochondrial membrane.
• A high amount of ATP is produced, about 32-36 ATP molecules occur through this process.
• Oxidative phosphorylation or the electron transport chain is what this is called.

Anaerobic Metabolism

• Pyruvate converts into lactic acid because the Krebs cycle does not have enough oxygen.
• Oxygen is not needed for lactic acid production.
• ATP can be formed from lactic acid.
• Anaerobic exercise leads to lactic acid build-up as a result of an insufficient oxygen supply.

Triglyceride Metabolism and Ketone Production

• Glycerol can enter the glucose metabolism pathway at the pyruvate level.
• Fatty acids can enter the glucose metabolism pathway at the acetyl-CoA level.
• Pyruvate can be turned into glucose if it is required.
• Once past pyruvate into acetyl-CoA, this process cannot be reversed.
• The body breaks down triglycerides for energy if there is no glucose.
• Glycerol enters at the level of pyruvate, converting to glucose, and fatty acids enter at the level of acetyl-CoA.
• Oxaloacetate converts to glucose without glucose present.
• An overproduction of acetyl-CoA is a result of fatty acids.
• Ketones (beta-hydroxybutyrate, acetoacetate, acetone) are created as a result of excess acetyl-CoA.
• ATP (energy) can be produced from ketones.