Notes on Digestive System Functions

Overview

• Discussion of the digestive process highlighting key functions and terms related to different regions of the gastrointestinal (GI) tract.
• Focus on chemical digestion, mechanical digestion, absorption, and special terms used in the digestive process.

Mouth

• Chemical Digestion:
  • Lingual Lipase: Initiates fat digestion.
  • Salivary Amylase: Begins starch digestion.
• Mechanical Digestion:
  • Mastication: Also known as chewing.
• Absorption:
  • Limited, but can absorb certain substances like Vitamin B12.
• Special Term:
  • Bolus: A lump of chewed food ready for swallowing.

Pharynx and Esophagus

• No chemical or mechanical digestion nor absorption.
• Primarily serve as transport pathways.
• Processes:
  • Deglutition: Swallowing.
  • Peristalsis: Rhythmic contraction and relaxation of muscles to move food.

Stomach

• Chemical Digestion:
  • Gastric Lipase: Active mostly in babies, less effective in adults due to pH.
  • Pepsin: Converts proteins to peptides, released as inactive pepsinogen.
  • Hydrochloric Acid (HCl): Denatures proteins, released by parietal cells.
  • Intrinsic Factor: Essential for B12 absorption, released by parietal cells.
  • Alcohol Dehydrogenase: Breaks down consumed alcohol.
• Mechanical Digestion:
  • Churning: Vigorous mixing of stomach contents.
• Absorption:
  • Water, certain drugs (e.g., aspirin), and some alcohol are absorbed.
• Special Terms:
  • Chyme: Partially digested, soupy food moving to the small intestine.
• Gastric Pits and Glands:
  • Gastric Pits: Contain mucous cells to release mucus, protecting stomach lining.
  • Gastric Glands: Composed of chief cells (release pepsin and lipase) and parietal cells (release HCl and intrinsic factor).
• Hormones and Cells:
  • G Cells: Secrete gastrin, which stimulates GI tract movement and secretion.

Small Intestine

• Major site for digestion and nutrient absorption.
• Receives chyme from the stomach through the pyloric sphincter.
• Designed to maximize surface area for absorption.

Key Takeaways

• Enzymes: Various enzymes play specific roles in breaking down different types of nutrients.
• Hormones: Gastrin plays a crucial role in regulating the movement and secretion in the digestive tract.
• Structural Features: Gastric pits and glands are essential for protecting the stomach and facilitating digestion.
• Absorption: While some absorption occurs in the stomach, the small intestine is the primary site for nutrient absorption.