Digestive Processes: Oral Cavity and Stomach

Overview

• Series of videos on digestive processes along the GI tract
• Focus of this video: Oral cavity and stomach

Digestive Processes in the Oral Cavity

• Ingestion:

  • Occurs in the oral cavity
  • Start of food intake

• Propulsion (Motility):

  • Moving food through the digestive tract
  • In the oral cavity, this involves swallowing (deglutination)

• Mechanical Digestion:

  • Chewing (mastication) to break food into smaller pieces
  • Mixes food with saliva, forming a bolus

• Chemical Digestion:

  • Salivary amylase: Enzyme in saliva that breaks down starch (a polysaccharide into monosaccharides)
  • Lingual lipase: Secreted by tongue, breaks down lipids (inactive until low pH in stomach)

Digestive Processes in the Stomach

• Focus on: Propulsion, Mechanical Digestion, Chemical Digestion, and Absorption

• Propulsion and Mechanical Digestion:

  • Mixing waves: Contractions that mix stomach contents
  • Gastric emptying: Movement of chyme from stomach to small intestine

• Chemical Digestion:

  • Lipid and protein digestion
  • Lingual lipase becomes active; gastric lipase also secreted
  • Hydrochloric acid (HCl) and pepsinogen create pepsin, breaking down proteins

• Absorption:

  • Limited absorption occurs in the stomach
  • Hydrophobic substances (e.g., alcohol) can diffuse through cell membranes

Protection Mechanisms in the Stomach

• Prevention of Autodigestion:
  • Pepsinogen secreted as inactive; activated by HCl to form pepsin
  • Mucus layer: Physical and pH barrier against gastric acid
  • Mucus contains mucin and bicarbonate ions to neutralize acid

Key Terms

• Amylase: Enzyme breaking down carbohydrates
• Lipase: Enzyme breaking down lipids
• Pepsinogen/Pepsin: Enzymes for protein digestion, activated by HCl
• Mucin: Protein chains forming mucus, protecting stomach lining

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Closing

• Next video will cover the rest of the digestive tract.