Digestive System Vocabulary Review

Overview of the Digestive System

• Lecture Objectives:
  • General features of the digestive system from oral cavity to large intestine and accessory organs.
  • Chemical and mechanical digestion sites across the gut tube.
  • Understanding the enteric nervous system.
  • Description of peritoneum folds.

Anatomy of the Digestive System

• Key Components:
  • Oral Cavity:
  • Contains teeth and tongue.
  • Involved in ingestion and initial mechanical digestion.
  • Salivary Glands:
  • Parotid, Submandibular, Sublingual Glands
  • Produce saliva to aid in digestion.
  • Esophagus:
  • Transports food from mouth to stomach.
  • Stomach:
  • J-shaped organ for mixing and digesting food.
  • Small Intestine:
  • Comprises the duodenum, jejunum, and ileum.
  • Primary site for chemical digestion and nutrient absorption.
  • Large Intestine:
  • Absorbs water, electrolytes; compacts waste.
  • Contains cecum, colon, rectum, and anus.

Digestion Fundamentals

• Types of Digestion:
  • Chemical Digestion: Breakdown of food by enzymes (e.g., saliva, gastric juice).
  • Mechanical Digestion: Physical breakdown of food (e.g., chewing, churning in stomach).

The Alimentary Canal

• A continuous tube from mouth to anus, modified into sections:
  • Ingestion
  • Mechanical Processing
  • Transport
  • Secretion
  • Chemical Changes
  • Absorption
  • Defecation

Layers of the Gut Tube

1. Mucosa: Innermost layer; contains epithelium, lamina propria.
2. Submucosa: Connective tissue layer with blood vessels, nerves.
3. Muscularis: Responsible for peristalsis (circular and longitudinal muscle layers).
4. Serosa: Outermost layer; visceral peritoneum.

Peritoneum

• Layers:
  • Parietal Peritoneum: Lines abdominal cavity.
  • Visceral Peritoneum: Covers abdominal organs.
  • Mesentery: Folds of the peritoneum that support organs, containing blood vessels and nerves.

The Digestive Tract

Mouth

• Structure:
  • Bounded by cheeks, palate, lips; contains vestibule and fauces.

Salivary Glands

• Functions of Saliva:
  • Hydrolyzes starch with salivary amylase.
  • Provides lubrication for swallowing.
  • Antimicrobial activity via lysozyme.

Teeth

• Types of Teeth:
  • Incisors: Biting.
  • Canines: Tearing.
  • Molars: Grinding.
• Components: Enamel, dentine, cementum.

Deglutition (Swallowing)

1. Voluntary Phase: Bolus pushed to oropharynx; triggers swallowing reflex.
2. Involuntary Phase: Peristalsis moves food through the esophagus.

Stomach

• Function:
  • Mixes bolus with gastric juices to form chyme.
  • Chemical Digestion: Pepsin or gastric lipase.
  • Mechanical Digestion: Waves of muscle contraction.

Small Intestine

• Sections: Duodenum, jejunum, ileum.
• Functions:
  • Chemical digestion via intestinal juices and enzyme activity.
  • Enhances absorption through villi and microvilli.

Pancreas

• Functions:
  • Endocrine: Hormone secretion (insulin, glucagon).
  • Exocrine: Produces digestive enzymes (e.g., amylase, lipase).

Liver and Gallbladder

• Liver Functions:
  • Produces bile for fat emulsification.
• Gallbladder: Stores bile until needed for digestion.

Large Intestine

• Mechanism: Peristalsis and haustral churning.
• Functions:
  • Absorption of water and electrolytes.
  • Formation of feces.
• Bacterial Fermentation: Conversion of nutrients and production of vitamins.

Defecation

• Reflex actions leading to expulsion of feces, driven by the gastrocolic reflex and activation of sacral nerves.

Control of Digestive Processes

• Enteric Nervous System:
  • Regulates digestive activities via sensory and motor neurons.
  • Influenced by autonomic nervous system (ANS).

Digestive Enzymes Summary

• Salivary: Salivary amylase, lingual lipase.
• Gastric: Pepsin, gastric lipase.
• Pancreatic: Amylase, lipase, trypsin, chemotrypsin, nucleases.
• Intestinal: Peptidase, intestinal lipase, sucrose.

Absorption of Water

• Approximately 9 liters of fluid secreted into the GI tract daily, with 8 liters reabsorbed by the small intestine.