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.