Chapter 24: The Digestive System

Overview

• The digestive system acquires nutrients from the environment.
  • Anabolism: Using nutrients to make essential compounds.
  • Catabolism: Breaking down food for cellular energy.

Main Components

• Digestive Tract (GI tract): Muscular tube from mouth to anus.
• Accessory Organs: Teeth, tongue, glands.

Main Processes

1. Ingestion: Entry of food into the mouth.
2. Mechanical Digestion and Propulsion: Breaking food into smaller pieces and moving it through the GI tract.
3. Chemical Digestion: Breaking down food chemically into small fragments.
4. Secretion: Release of water, acids, enzymes from digestive glands.
5. Absorption: Movement of nutrients into interstitial fluid.
6. Defecation: Elimination of waste.

Serous Membranes

• Peritoneum: Lines the peritoneal cavity.
  • Visceral Peritoneum: Covers organs.
  • Parietal Peritoneum: Lines body wall.
• Mesenteries: Support digestive tract portions.

Key Structures

• Lesser Omentum: Stabilizes stomach.
• Greater Omentum: Protects abdomen, stores fat.
• Mesentery Proper: Supports small intestine.
• Mesocolon: Supports the large intestine.

Histology of the Digestive Tract

• Mucosa: Innermost layer, contains epithelial tissue.
• Submucosa: Dense connective tissue.
• Muscular Layer: Smooth muscle for movement.
• Serosa: Outermost layer covering.

Motility

• Peristalsis: Moves food along the GI tract.
• Segmentation: Mixes contents in intestines.

Regulation of Digestive Functions

• Local Factors: pH, volume, chemical composition.
• Neural Mechanisms: Control muscle contraction.
• Hormonal Mechanisms: Affect digestion processes.

Oral Cavity

• Functions: Sensory analysis, mechanical digestion, lubrication, limited digestion.
• Tongue: Assists in mechanical digestion, speaking.
• Teeth: Aid in mechanical digestion.
• Salivary Glands: Secrete enzymes for digestion.

Esophagus

• Function: Transports food to the stomach.
• Histology: Stratified squamous epithelium.
• Swallowing (Deglutition): Voluntary and involuntary phases.

Stomach

• Functions: Temporary storage, mechanical and chemical digestion.
• Regions: Cardia, Fundus, Body, Pylorus.
• Histology: Contains gastric pits and glands.

Pancreas and Liver

• Pancreas: Produces enzymes for digestion.
• Liver: Produces bile, processes nutrients.

Small Intestine

• Segments: Duodenum, Jejunum, Ileum.
• Functions: Chemical digestion, absorption.
• Histology: Circular folds, villi, microvilli.

Large Intestine

• Functions: Absorption of water, vitamins, elimination of waste.
• Regions: Cecum, Colon, Rectum.
• Microbes: Aid in digestion, vitamin production.

Additional Topics

• Digestive Enzymes: Break down carbs, proteins, lipids.
• Age-related Changes: Decline in stem cells, muscle tone.

Interconnection with Other Systems

• The digestive system is connected to the nervous, cardiovascular, endocrine, and lymphatic systems and acts as an endocrine organ.

Next Topic: The Urinary System