Digestive System Overview

Introduction

• Presenter: Dr. Morton, noted anatomist
• Focus: Digestive system organs, functions, accessory organs, vascular supply, and innervation.

Digestive Organs and Their Functions

Oral Cavity

• Teeth: Mastication (physical breakdown of food)
  • Mandible aids in chewing
  • Physical digestion reduces food size without breaking chemical bonds.
• Salivary Glands: Chemical digestion of carbohydrates
  • Types: Submandibular, Parotid, Sublingual
  • Submandibular produces most saliva (75-80%)
  • Saliva forms a bolus, contains enzymes (salivary amylase) for carbohydrate digestion.

Esophagus

• Transports food from oral cavity to the stomach
• Muscle types:
  • Proximal: Skeletal muscle (voluntary)
  • Middle: Mixed
  • Distal: Smooth muscle (involuntary)
• Peristalsis: Involuntary movement propelling food through the GI tract.

Layers of the GI Tract

• Mucosa: Lined with epithelium, absorption, and secretion
  • Contains lamina propria with capillaries and lymphatics
• Submucosa: Dense connective tissue, blood vessels
• Muscularis Externa: Smooth muscle layers
  • Inner circular and outer longitudinal layer
  • Responsible for segmentation and peristalsis
• Serosa: Visceral peritoneum, serous fluid production

Stomach

• Location: Between esophagus and duodenum
• Function:
  • Peristaltic movements convert bolus to chyme
  • Goblet cells produce mucus; parietal cells produce hydrochloric acid
  • Chief cells secrete pepsinogen for protein digestion.
• Regions: Cardia, Fundus, Body, Pylorus
• Sphincters: Cardiac and Pyloric

Small Intestine

• Length: ~7 meters, small lumen diameter
• Parts: Duodenum, Jejunum, Ileum
• Duodenum: First section, chemical digestion, and nutrient absorption
  • Contains Bruner's glands and receives bile and pancreatic enzymes
• Jejunum and Ileum: Absorption, fewer circular folds in the ileum
  • Ileum has Peyer's patches for immunity

Large Intestine

• Length: ~1.5 meters, larger diameter
• Function: Absorb water, salts, compact feces
• Regions: Cecum, Colon (Ascending, Transverse, Descending, Sigmoid), Rectum
  • Contains features like teniae coli, haustra, and epiploic appendages

Accessory Digestive Organs

Liver

• Location: Upper right quadrant
• Functions: Bile production, metabolism, detoxification
• Lobes: Right, Left, Quadrate, Caudate
• Portal Triad: Hepatic artery, portal vein, bile duct

Gallbladder

• Stores and concentrates bile
• Connected to the liver and small intestine via the biliary tree

Pancreas

• Location: Deep to the stomach, mostly retroperitoneal
• Exocrine function: Produces digestive enzymes (proteases, amylase, lipase)
• Endocrine function: Produces insulin and glucagon

Spleen

• Not a digestive organ but shares blood supply
• Functions in immune response and red blood cell recycling

Vascular Supply and Innervation

• Arterial Supply:
  • Foregut: Supplied by the celiac trunk
  • Midgut: Supplied by the superior mesenteric artery
  • Hindgut: Supplied by the inferior mesenteric artery
• Venous Drainage:
  • Mirrors arterial supply
  • Drains into the hepatic portal system
• Innervation:
  • Sympathetic: Reduces GI activity (splanchnic nerves)
  • Parasympathetic: Increases digestion (vagus nerve)

Summary

• A comprehensive look at the digestive system from ingestion to defecation.
• Understand the anatomical and functional aspects of each organ.
• Recognize the integration of vascular supply and nerve innervation in the digestion process.