Digestive System

introduction

Overview Gastrointestinal Tract (GI Tract) – from mouth to anus Accessory organs – teeth, tongue, salivary glands, liver, gallbladder, pancrea s

Functions Ingestion Secretion – H20, enzymes, acid, buffers Mixing and propulsion – peristalsis Digestion – mechanical and chemical breakdown Absorption Defecation

structures

Mouth, Pharynx & Esophagus Mouth includes teeth, tongue, salivary glands Pharynx – throat; swallowing reflex Esophagus – muscular tube; transports food to the stomach; some absorption

Stomach J-shaped enlargement of the GI tract Gastric Juice: Mucus Pepsinogen HCl Intrinsic factor Chyme: thick liquid of gastric juice and food

Stomach 4 Layers of stomach wall Mucosa Secretory Cells Rugae – folds of stomach wall Columnar epithelium – secretes mucus Secretory Cells Mucus cells Parietal Cells – HCl and Intrinsic factor (vit. B12 absorption) Chief cells – secrete pepsinogen G cells – secrete gastrin

Stomach Muscularis 3 layers of muscle Serous Membrane Forms the greater omentum and mesentery

Small Intestine 3 sections: duodenum, jejunum, ileum Most of digestion and absorption takes place here Absorptive cells in the microvilli Absorption of sugars, amino acids, H2O, lipids, vitamins Digestive enzymes come from pancreas and small intestine

Small Intestine Digestive enzymes: Maltase, sucrase, lactase Lipase Absorption: Simple sugars, amino acids, ions, H2O, lipids, and vitamins

Large Intestine 1st section at opening of ileum – cecum; appendix attached 4 regions: ascending, transverse, descending, and sigmoid colon Final stage of digestion (work of bacteria) Absorption of H2O, vitamins Chyme → feces → defecation (elimination)

Pancreas Pancreatic juice: H2O, salts, HCO3-, enzymes Enzymes: Amylase; breaks down starches Trypsin; breaks down proteins (inactive form) Lipase; breaks down fats

Liver & Gallbladder Bile: emulsifies large lipid globules; stored in gallbladder Functions: Carbohydrate metabolism – blood glucose levels Lipid metabolism – cholesterol production, etc. Protein metabolism – ATP production, converting ammonia into urea, plasma protein production

Liver & Gallbladder Functions (continued) Processes drugs and hormones; detox center Stores minerals and vitamins Activates vitamin D