Lecture Notes on the Digestive System

Introduction

• Presenter: Dr. Morton, noted anatomist
• Topic: Digestive system
  • Digestive system organs and their functions
  • Accessory digestive organs' contribution to digestion
  • Vascular supply and innervation of the GI tract

Digestive Organs

Oral Cavity

• Teeth: Responsible for mastication (physical digestion)
  • Breaks down food into smaller pieces
• Salivary Glands:
  • Produce saliva which moistens food and forms a bolus
  • Salivary Amylase: Initiates chemical digestion of carbohydrates
  • Three main glands:
    • Submandibular (75-80% saliva production)
    • Parotid (15-20%)
    • Sublingual (2-3%)

Esophagus

• Transports food from oral cavity to stomach
• Muscle architecture:
  • Proximal: Skeletal muscle (voluntary)
  • Distal: Smooth muscle (involuntary)
  • Middle: Mix of skeletal and smooth muscle
• Peristalsis: Involuntary movement aiding in food transport

Layers of the GI Tract

1. Mucosa: Epithelium, lamina propria; absorption and secretion
2. Submucosa: Dense connective tissue, larger vessels, and nerves
3. Muscularis Externa: Inner circular and outer longitudinal smooth muscle
   • Segmentation and peristalsis
4. Serosa: Mesothelial lining (visceral peritoneum)

Stomach

• Located between esophagus and duodenum
• Functions:
  • Churns and converts bolus into chyme
  • Goblet Cells: Produce mucus
  • Parietal Cells: Produce hydrochloric acid and intrinsic factor
  • Chief Cells: Secrete pepsinogen (protein digestion)
• Regions: Cardia, fundus, body, pylorus

Small Intestines

• Sections: Duodenum, jejunum, ileum
• Duodenum: Four parts, Brunner’s glands
• Jejunum and Ileum:
  • Circular folds for absorption
  • Jejunum: More folds; Ileum: Fewer folds, Peyer's patches

Large Intestines

• Length: 1.5 meters
• Functions: Absorption of water, salts, vitamins
• Features: Teniae coli, haustra, epiploic appendages
• Parts: Cecum, colon (ascending, transverse, descending, sigmoid), rectum

Accessory Digestive Organs

Liver

• Located in upper right quadrant
• Functions: Produces bile, detoxifies blood, produces proteins
• Lobes: Right, left, quadrate, caudate

Gallbladder

• Stores and concentrates bile

Pancreas

• Location: Deep to stomach
• Functions:
  • Exocrine: Digestive enzymes
  • Endocrine: Insulin and glucagon

Spleen

• Not a digestive organ
• Functions: Stores blood, removes defective red blood cells

Vascular Supply and Innervation

Embryonic Gut Division

• Foregut: Stomach to duodenum (accessory organs)
• Midgut and Hindgut: Duodenum to rectum

Arterial Supply

• Celiac Trunk: Foregut organs
• Superior Mesenteric Artery (SMA): Midgut organs
• Inferior Mesenteric Artery (IMA): Hindgut organs

Venous Drainage

• Hepatic Portal System
  • Foregut: Gastric, gastro-omental, splenic veins
  • Midgut: Superior mesenteric vein
  • Hindgut: Inferior mesenteric vein

Innervation

• Sympathetic: Reduces peristalsis
• Parasympathetic: Increases peristalsis
  • Foregut: Greater splanchnic nerve, vagus nerve
  • Midgut: Lesser splanchnic nerve, vagus nerve
  • Hindgut: Lumbar splanchnic nerves, pelvic splanchnic nerves

Summary

• Digestive processes from oral cavity to anus
• Integration of vascular supply, venous drainage, innervation
• Importance of accessory organs in digestion