19) Energy and Metabolism

• We gain most energy from chemical bonds in food.

  • When digested it can release different amounts of ATP
• Bond energy = Energy intake - Energy output
• Energy output = Work + Heat
• Main sources of work include:

  • Biological transport
  • Mechanical work
  • Chemical Work
• Metabolites are absorbed through ”Gut epithelial cells” and processed in the liver
• Metabolite I: Carbohydrates

  • Absorbed actively and passively
  • Glucose is the most important metabolite as its the only thing the brain uses for energy
  • Stored in the body as glycogen in the liver and muscles, but excess it converted into triglycerides
• Glycolysis of 1 Glucose = 2 ATP
• Metabolite II: Proteins

  • Aquired from diet and turnover of gut membranes
  • Used to make lipoproteins, structural proteins, enzymes, hormones, muscle
  • Excess amino acids are converted into fat
• Protein absorption relies on Na+, H+, K+ ions within the gut epithelial cells and passive carriers
• Digestion of fats:

  • Triglycerides are water-insoluble and require bile salts to emulsify them to increase their SA for Lipase to work on
  • When Hydrolysed, monoglycerides and fatty acids are packaged into micelles and transported into chylomicrons
  • Chylomicrons are exocytosed into lymphatic vessels
• KiloCalories (kCal) are the unit of energy.

  1. 1 Gram of glucose = 4 kCal
  2. 1 Gram of Protein = 4 kCal
  3. 1 Gram of Fat = 1 kCal
• Metabolic rate is influenced by:

   -  Age and gender

   - Amount of lean muscle mass: Muscle uses more energy

   - Activity level

   - Type of diet 

   - Hormones: THYROID and CATECHOLAMINES

   - Genetics (FTO)

   - Energy intake and level of physical acitivy
• Insulin and glucagon is produced in the pancreas
• • Alpha cells produce glucagon
  • Beta cells produce Insulin and Amyli
• Factors that control insulin release:

  1. incr amino acid and plasma glucose concentration
  2. Feed-forward effects of gastrointestinal hormones (hormones involved in metabolism)
  3. Parasympathetic activity
  4. Sympathetic activity
• Insulins main function is to reduce glucose levels 

   ⤷ 1) Stimulated incr expression of glucose transporters

    2) Incr sensitivity of GLUT (Without incr number of cells) 

   3) Enhances anabolic pathways 

  4) Enhance use of amino acids and protein synthesis

  5) Enhances fat synthesis