Digestive System Overview

Alimentary Canal Definition

• Continuous tube from mouth to anus for food digestion.
• Includes all organs involved in ingestion, digestion, and excretion.

Main Digestive System Organs

• Mouth
• Pharynx
• Esophagus
• Stomach
• Small intestine (duodenum, jejunum, ileum)
• Large intestine (cecum, colon, rectum, anal canal)
• Anus

Accessory Digestive System Organs

• Salivary glands (parotid, submandibular, sublingual)
• Liver
• Gallbladder
• Pancreas

Food Processes During Ingestion

• Digestion: Mechanical and chemical breakdown into absorbable molecules.
• Absorption: Uptake of nutrients into bloodstream through intestinal walls.
• Metabolism: Conversion of food into energy (anabolism/catabolism).

Mouth Structure and Function

• Hard & Soft Palate: Hard palate for chewing, soft palate for nasal closure during swallowing.
• Uvula: Prevents food from entering the nasal cavity during swallowing.
• Tongue: Manipulates food for chewing, tasting, and swallowing.
• Teeth: Incisors, canines, premolars, molars for cutting, tearing, crushing, and grinding.
• Mastication: Chewing breaks down food mechanically.
• Salivary Glands: Produce saliva with enzymes (amylase) for carbohydrate digestion and lubrication.

Pharynx Structure and Function

• Location: Behind the mouth and nasal cavity, connecting to esophagus and larynx.
• Structure: Muscular tube with nasopharynx, oropharynx, and laryngopharynx regions.
• Function: Passageway for food and air, directing both to appropriate destinations.

Digestive Tract Wall Layers

• Lumen: The hollow space through which food passes.
• Mucosa: Innermost layer for secretion and absorption.
• Submucosa: Connective tissue layer with blood vessels, nerves, and glands.
• Muscularis: Smooth muscle for peristalsis and segmentation.
• Serosa: Outermost connective tissue layer (peritoneum), reducing friction.

Esophagus Structure and Function

• Location/Length: 10 inches (25 cm) from pharynx to stomach.
• Structure: Mucosa, submucosa, muscularis, and serosa layers.
• Epiglottis: Covers trachea during swallowing to prevent food aspiration.
• Esophageal Hiatus: Opening in diaphragm for esophagus.
• Cardioesophageal Sphincter (lower esophageal sphincter): Prevents reflux.

Stomach Structure and Function

• Fundus, Body, Pylorus: Regions of the stomach.
• Pyloric Sphincter: Regulates chyme release to small intestine.
• Greater & Lesser Curvatures: Outer and inner stomach curves, attachment points for omentum.
• Muscle Layers: Facilitate churning and mixing.
• Mucosa: Inner layer with gastric glands for secretion.
• Rugae: Folds for expansion.
• Peristalsis: Mixing and propulsion.
• Chyme: Mixture of food and gastric juices.
• Gastric Glands: Secrete hydrochloric acid, pepsinogen, and mucus.

Small Intestine Structure and Function

• Duodenum, Jejunum, Ileum: Segments of small intestine.
• Plicae Circularis: Circular folds increasing surface area.
• Intestinal Villi & Microvilli: Increase surface area for nutrient absorption.
• Intestinal Glands: Secrete enzymes and mucus.
• Blood Supply: From mesenteric arteries for nutrient delivery.
• Lacteals: Lymphatic vessels absorbing fats.
• Ileo-cecal Valve: Controls chyme flow to large intestine.

Liver and Gallbladder

• Location: Liver in upper right quadrant, gallbladder below liver.
• Hepatic Duct: Carries bile from liver.
• Cystic Duct: Connects gallbladder to common bile duct.
• Common Bile Duct: Conduit to duodenum.
• Bile: Fluid aiding in fat emulsification and digestion.
• Location of bile production: Liver, storage: gallbladder.

Pancreas Structure and Function

• Exocrine & Endocrine Portions: Produces digestive enzymes and hormones.
• Pancreatic Duct: Carries enzymes to duodenum.
• Relationship to Common Bile Duct: Merger before entering duodenum.
• Exocrine Secretions: Enzymes and bicarbonate to neutralize stomach acid.
• Endocrine Hormones: Insulin (lowers glucose), glucagon (raises glucose).

Large Intestine Structure and Function

• Ileo-cecal Valve: Regulates chyme flow.
• Cecum: Receives chyme from ileum.
• Appendix: Vestigial organ with suspected immune function.
• Colon (Ascending, Transverse, Descending, Sigmoid): Sections for water and salt absorption, waste storage.
• Rectum: Stores feces before expulsion.
• Anus: Fecal excretion opening.
• Anal Sphincters: Voluntary & Involuntary muscles for continence.
• Teniae Coli: Longitudinal bands for contraction.
• Haustra: Pouches formed for contraction and water absorption.
• Blood Supply: Superior & Inferior mesenteric arteries.

Peritoneum

• Location: Serous membrane lining abdominal cavity.
• Parietal Peritoneum: Lines abdominal wall.
• Visceral Peritoneum: Covers abdominal organs.
• Function: Reduces friction, supports organs, and conduits for blood vessels and nerves.

Mesentery and Greater Omentum

• Mesentery: Attaches intestines to posterior abdominal wall, provides support, and pathways for blood vessels and nerves.
• Greater Omentum: Drapes over intestines, provides insulation, fat storage, and immune functions (macrophages).