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The Digestive System Functions • Ingestion • Mechanical digestion • Chemical digestion • Movements • Absorption • Elimination Mouth Teeth Pharynx & Esophagus • Both oropharynx and laryngopharynx • Esophagus Stomach Gastric Secretions •Mucus •HCl •Intrinsic factor •Pepsinogen •Gastrin Regulation of Gastric Secretion • Cephalic • Gastric • Intestinal • Stomach emptying • 4 hours • Liquids and carbs move out fast • Proteins and fatty acids take longer Small Intestine • Functions • Finishes digestion • Absorbs nutrients • Passes waste to large intestine Small Intestine Secretions • Neutral/alkaline fluid • Mucus • Peptidase • Maltase, sucrase, lactase • Lipase • Secretin & cholecystokinin Large Intestine Large Intestine Functions • Absorption of fluids and electrolytes • Waste elimination Liver • Produces and secretes bile • Bile salts • Many other non-digestive functions including: plasma proteins, storing glucose, detoxification of blood, and biomolecule metabolism Gallbladder • Stores and concentrates bile Pancreas • Endocrine function for glucose homeostasis • Digestive functions: • Amylase • Trypsinogen/trypsin • Lipase Chemical Digestion • Breaks down complex molecules into smaller ones that can be absorbed by cells • Uses the process of hydrolysis Carbohydrate Digestion • Begins in the mouth • Polysaccharides are broken down to disaccharides • In the small intestines, disaccharides are broken down into monosaccharides – glucose, fructose, and galactose Protein Digestion • Begins in the stomach • Breaks proteins into polypeptides • In the small intestines, peptides are reduced to amino acids (the building blocks of proteins) Lipid Digestion • Only occurs in the small intestine • Fats are emulsified by bile to decrease attraction between the molecules • Lipids are broken down to monoglycerides and fatty acids (the building blocks of lipids) The Bottom Line • We ingest approximately 10 liters of materials a day. • 9 liters or more are absorbed in the small intestine. • A meal takes approximately 24-72 hours to make a complete journey through the digestive tract.
