Fluids, Electrolytes & Nutrition: Macronutrient Metabolism

Carbohydrates

Sugars

  • Monosaccharides (Single Units):
    • Glucose
    • Fructose
    • Galactose
  • Disaccharides (2 Units):
    • Sucrose: Glucose-Fructose
    • Lactose: Galactose-Glucose
    • Maltose: Glucose-Glucose
  • Oligosaccharides (3-10 or 12 Units):
  • Polysaccharides (> 10-12 Units):
    • Starch
    • Glycogen
    • Cellulose
    • Chitin
    • Pectin

Digestion & Absorption

  • Digestion:
    • Begins in the Mouth with Salivary Amylase (Ptyalin)
      • Inactivated by Stomach Acid
    • Further Digested in Small Intestine by Pancreatic Amylase
  • Absorption:
    • Only Absorbed as Monosaccharides:
      • Secondary Active Transport – Glucose & Galactose
      • Facilitated Diffusion – Fructose Mn
    • Oligosaccharides that Cannot Be Broken Down or Absorbed are Fermented by Colonic Bacteria to Produce Short-Chain Fatty Acids (Primary Fuel of Colonocytes)

Fat

Fatty Acid Saturation

  • Saturated Fatty Acids
    • Definition: No Double Bonds Linking Adjacent Carbons
    • Higher Melting Point – More Likely to Be Solid at Room Temperature
  • Unsaturated Fatty Acids
    • Definition: At Least One Double Bond Linking Adjacent Carbons
    • Level of Saturation:
      • Monounsaturated Fatty Acids: Single Double Bond
        • Decrease LDL & Maintain HDL
      • Polyunsaturated Fatty Acids: Multiple Double Bonds
    • Bond Side:
      • Cis-Bonds – Abundant in Natural Sources
      • Trans-Bonds – Produced After Processing of Fats
        • More Adverse Cardiovascular Effects

Essential Fatty Acids

  • Definition: Fatty Acids That Humans Cannot Synthesize & Must Consume
  • Includes:
    • Linolenic Acid
    • Alpha-Linolenic Acid
  • Essential Fatty Acid Deficiency
    • Effects:
      • Diffuse Scaly/Waxy Dermatitis
      • Alopecia
      • Thrombocytopenia
      • Intellectual Disability
    • Causes:
      • Infants Fed Diets Deficient in EFAs (Skim-Milk Formula) – Most Common
      • Chronic Total Parenteral Nutrition (TPN) with Inadequate Supplementation

Digestion & Absorption

  • Digestion:
    • Digestion Begin in Mouth with Lingual Lipase
    • Bile & Pancreatic Lipase Breakdown Triglycerides to Individual Fatty Acids
    • Fatty Acids Aggregate into Micelles
  • Absorption:
    • Fatty Acids Then Diffuse into Small Intestine Epithelial Cells & Recombine Back into Triglycerides
    • Triglycerides & Cholesterol are Packaged into Chylomicrons
    • Chylomicrons are Then Absorbed into Lacteals to Directly Enter the Lymphatic Circulation & Transport into the Bloodstream

Protein

Amino Acids (AA)

  • Nonessential Amino Acids
    • Definition: Humans Can Make & Do Not Need to Consume
    • Includes: Alanine, Arginine, Asparagine, Aspartic Acid, Cystine, Glutamic Acid, Glutamine, Glycine, Proline, Serine & Tyrosine
    • Conditional Amino Acids
      • Definition: Usually Nonessential but Can Become Essential in Times of Stress or Illness
      • Includes: Arginine, Cystine, Glutamine, Glycine, Proline, Serine & Tyrosine
  • Essential Amino Acids
    • Definition: Humans Cannot Make & Need to Consume
    • Includes: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan & Valine Mn
    • Branched Chain Amino Acids: Mn
      • Leucine
      • Isoleucine
      • Valine

Digestion & Absorption

  • Broken Down by Pepsin (Stomach) & Trypsin/Chymotrypsin (Pancreatic Enzymes)
  • Absorbed in the Small Intestine
    • 50% in the Duodenum
  • Absorbed as Single Amino Acids, Dipeptides & Tripeptides
    • Most Peptides Longer than Four Amino Acids are Not Absorbed

Degradation

  • Protein Degradation:
    • Ubiquitin-Proteasome Pathway:
      • Proteins are Marked for Degradation by the Attachment of Ubiquitin
      • Polyubiquitinated Proteins are Recognized & Degraded by Proteasomes
    • Lysosomal Proteolysis Pathway:
      • Proteins are Taken Up by Lysosomes
      • Lysosomal Proteases Then Degrade Proteins
    • Result in Nitrogenous End Products (Ammonia)
  • Nitrogen Elimination:
    • Urea Cycle – Converts Ammonia to Urea
      • Arginine is the Immediate Precursor to Urea
    • Primarily Occurs in the Liver, Somewhat in the Kidney
    • Urea is Then Excreted in the Kidney

Mnemonic

Monosaccharide Absorption

  • F:F – Fructose Absorbed by Facilitated Diffusion
  • Others by Secondary Active Transport

Essential Amino Acids

  • “PVT TIM HALL”
  • Includes: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan & Valine

Branched Chain Amino Acids

  • “Louisville (Leu-Val) Sluggers” (Baseball Bats – Lumber/Branches)
    • Leucine
    • Isoleucine
    • Valine