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Digestion Topic 6.1 Terminology • Ingestion: – Food entering the body • Digestion – Series of reactions where the food is broken down into smaller and smaller molecules. • Absorption – Food entering nearby blood and lymphatic vessels. • Assimilation – Process of bringing the nutrient to a body cell and then using it. • Transport – Circulatory system delivers the small molecular nutrients to your body cells. Digestive Anatomy • • • • • • • Mouth • Gall Bladder Esophagus • Pancreas Stomach • Liver Small Intestine Large Intestine (colon) Rectum Anus Digestive Enzymes • Enzymes are needed to break larger molecules into smaller one. (macromolecules into monomers) • Enzymes have substrate specificity • Lowers the activations energy necessary for reaction to occur • Cellulose(plant cell walls ) cannot be digested. Known as Fiber Molecule Ingested Form Digested Form Proteins Protein Amino Acids Lipids Triglycerides Glycerol and Fatty Acids Carbohydrates Poly, Mono, Disaccharides Monosaccharides Nucleic Acids DNA, RNA Nucleotides Common Digestive Enzymes Salivary Amylase Endopeptidase (protease) Pancreatic Lipase Source Salivary Glands Stomach Cells Pancreas Cells Substrate Amylose (starch) Proteins (polypeptides) Lipids Products Maltose and glucose Amino Acids Glycerol and Fatty Acids Optimum pH Neutral (pH 7) Acidic (pH 3) Neutral (pH 7) Peristalsis • The contraction of both longitudinal and circular muscles (smooth muscle) • Circular muscles constrict to make sure food travels one way • Longitudinal muscles moves food along • These muscles exert continuous, moderate force rather than periods of rest and then contraction Cell layers of small intestine Micrograph of small intestine Small Intestine • Bile: - Produced by the liver and secreted by the gall bladder - Digests fats • Digestive enzymes: -secreted by the pancreas -endopeptidase (protease), lipase and Amylase • Villi • Small projections that are responsible for absorption of nutrients • Contains capillary beds for rapid absorption and transport. Villi • Digested nutrients and vitamins and minerals either enter the lacteal or the capillary beds. (absorption) • Single layer of epithelial cells allows for rapid diffusion. • Increased surface area for maximum absorption Surface of small intestine Methods of Absorption • Different methods of membrane transport are required to absorb different nutrients. • Nutrients must pass from the lumen of the small intestine to the capillaries/lacteals in the villi • They must first pass through the epithelial cells • Simple diffusion, facilitated diffusion, active transport and exocytosis Absorption of triglycerides 1. Triglycerides digested into fatty acids and monoglycerides 2. Monoglycerides diffuse into epithelial cells by simple diffusion (can pass through the phospholipid bi-layer) 3. Fatty acids are absorbed by facilitated diffusion (fatty acid transport proteins) 4. In the epithelial cells, triglycerides are reformed, join with cholesterol and become covered with phospholipids 5. Sent out of epithelial cells via exocytosis Absorption of triglycerides Absorption of Glucose • Glucose is polar and cannot pass through phospholipids • Sodium/potassium pump allows glucose to pass through (sodium-glucose co-transporter protein) into epithelial cells • Glucose channels allow glucose to move by facilitated diffusion into the capillaries Absorption of Glucose
