Chapter 4

• Utilization


  Processes that nutrients undergo during digestion, absorption, metabolism, and excretion
• Metabolism


  Breakdown of food and its subsequent transformation into energy the body needs
• Digestion


  Mechanism of breaking down large, indissoluble food molecules into smaller ones for absorption into the bloodstream
• Types of Digestion


  • Mechanical Processes
  • Chemical Processes
• Mechanical Processes


  • Chewing and swallowing
  • Storage, mixing, controlled emptying
• Chemical Processes


  • Enzymatic actions
• Enzymes


  • Protein in nature
  • Initiate and accelerate chemical reactions
• Proenzymes / Zymogens


  Inactive form
• Cofactor


  Zinc / vitamin need to be functional
• Digestive Enzymes


  • Amylase - starch splitters
  • Lipase - fat splitters
  • Protease - protein splitters
• Substrate


  Substance acted upon by an enzyme
• Bioavailability


  Amount of nutrient in a food that the body may use to perform physiological functions
• Factors affecting bioavailability


  • Digestion, absorption, and distribution of the nutrient by the circulating blood
  • Entry of the nutrient into the specific body tissues and fluids
• Absorption


  Action of taking in or assimilating substances into cells across tissues and organs
• Digestion and Absorption of Carbohydrates

  1. Mouth: Digestion starts with saliva containing amylase, small portion converted to dextrin and maltose

  2. Bolus → Esophagus → Stomach: No digestion occurs

  3. Mixing of Chyme in Duodenum: Chyme mixes with digestive secretions

  4. Pancreatic Juices breaks up Starch and Glycogen: Amylase breaks down starch and glycogen into maltose and other disaccharides

  5. Enzymatic Breakdown of Disaccharides into Mono: Enzymes like maltases, sucrases, lactases break down disaccharides
• Absorption of Simple Sugars

  Through simple diffusion and active transport
• Glucose and Galactose


  Absorbed by facilitated diffusion
• Digestion and Absorption of Proteins

  1. Pepsin digests protein in ingested food

  2. Hydrochloric Acid activates pepsinogen → pepsin

  3. Parietal Cells lower pH level of stomach to activate pepsin

  4. Enterokinase converts trypsinogen to trypsin

  5. Trypsin and Chymotrypsin hydrolyze peptide bonds of polypeptides

  6. Carboxypeptidase hydrolyzes peptide bonds of carboxyl group

  7. Brush Boro Enzymes hydrolyze peptide bonds into smaller molecules

  8. Dipeptidase hydrolyzes dipeptides

  9. Aminopeptidase hydrolyzes amino group

  10. Small Peptides absorbed in intestinal cells with hydrogen

  11. Peptidase hydrolyzes peptides into amino acids

  12. Amino Acids diffuse to blood stream

  13. Hydrogen goes out from intestinal cells, Sodium absorbed within the cell

  14. Amino Acids enter cells with sodium

  15. Blood Stream carries protein to the liver
• Digestion and Absorption of Fats / Lipids

  1. Triglycerides breakdown in the mouth with lingual lipase and mastication

  2. Packaged up as chylomicrons in the small intestine before being transported via the lymphatics

  3. CCK stimulates pancreatic enzyme release → pancreatic juice

  4. Secretin stimulates bicarbonate secretion from pancreas

  5. Bile Salt emulsifies and coats the lipids which allow digestion by the pancreatic lipases

  6. Pancreatic Lipases help break down triglycerides further into fatty acids

  7. Micelles composed of bile salts, fatty acids, monoglycerides, cholesterol, and phospholipids