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

Stomach4 Layers of stomach wall• Mucosa– 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• LipaseAbsorption:• 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