Lecture Notes: Anatomy of the Digestive System

Overview

• Digestive System: A group of organs that work together to break down food into smaller molecules for absorption.
• Gastrointestinal (GI) Tract: Tube from mouth to anus, also called alimentary canal.
• Accessory Organs: Teeth, tongue, salivary glands, liver, gallbladder, pancreas.
• Digestive Processes: Ingestion, secretion, motility, digestion, absorption, defecation.

Digestive System Functions

1. Ingestion: Taking food and liquids into the mouth.
2. Motility: Moving and mixing materials through GI tract via smooth muscle contractions.
3. Secretion: Release of water, acid buffers, and enzymes (approximately 7 liters/day).
4. Digestion:
   • Mechanical: Physical breakdown (chewing, churning).
   • Chemical: Breakdown into carbohydrates, lipids, proteins, nucleic acids using enzymes.
5. Absorption: Moving nutrients into blood/lymphatic system.
6. Defecation: Expulsion of undigested materials.

GI Tract Layers

1. Mucosa: In contact with food, fast cell turnover.
2. Submucosa: Contains blood/lymphatic vessels and neurons.
3. Muscularis: Two muscle layers (inner circular, outer longitudinal).
4. Adventitia/Serosa: Superficial tissue, covered by visceral peritoneum.

Peritoneum and Abdominal Cavity

• Peritoneum: Largest serous membrane, compartmentalizes abdominal organs.
• Five Folds: Greater omentum, lesser omentum, falciform ligament, mesentery, mesocolon.

Individual Organs

Oral Cavity

• Structures: Hard/soft palate, uvula, cheeks, lips, vestibule, oral cavity proper, frenulums.
• Salivary Glands: Parotid, submandibular, sublingual.

Esophagus

• Function: Transports food from pharynx to stomach.
• Sphincters: Upper (voluntary), lower (involuntary).

Stomach

• Regions: Cardia, fundus, body, pyloric antrum/canal.
• Function: Mixes food with gastric juices to form chyme, minimal absorption.

Pancreas

• Function: Produces enzymes for digestion, sodium bicarbonate to neutralize stomach acid.

Liver

• Functions: Metabolism, detoxification, bile production.
• Bile: Emulsifies fats.

Gallbladder

• Function: Stores bile produced by liver.

Small Intestine

• Regions: Duodenum, jejunum, ileum.
• Function: Main site of nutrient absorption.

Large Intestine

• Regions: Cecum, colon (ascending, transverse, descending, sigmoid), rectum, anal canal.
• Function: Absorbs remaining water, forms and expels feces.

Clinical Views

• Vomiting: Expulsion of stomach contents, can lead to alkalosis.
• Cirrhosis: Liver tissue replaced by scar tissue, often due to alcohol or viral hepatitis.
• Jaundice: Yellowing of skin due to bilirubin buildup.
• Appendicitis: Inflammation of appendix, risk of rupture.
• Diarrhea/Constipation: Issues with stool consistency and frequency.

These notes highlight the main components and functions of the digestive system, focusing on anatomy and physiological processes, as well as providing insights into some clinical conditions related to the digestive system.