26 Digestive Physiology

Page 1

  • Title: Physiology of the Digestive System

    • Copyright Information: © 2007, 2003 by Mosby, Inc.

Page 2: Overview of Digestive Function

  • Primary Function: To bring essential nutrients into the internal environment for cellular availability.

  • Mechanisms of Digestive System:

    • Ingestion: Intake of food.

    • Digestion: Breakdown of complex nutrients into simpler forms.

    • Motility: Movement and physical breakdown of food through the GI wall.

    • Secretion: Release of digestive enzymes for chemical digestion.

    • Absorption: Movement of nutrients into the internal environment via the GI mucosa.

    • Elimination: Excretion of non-absorbed materials.

    • Regulation: Coordination of digestive functions.

  • Digestive tract serves as an extension of the external environment until absorption occurs.

Page 3: Mechanical Digestion

  • Definition: Movements that change food from large to minute particles, facilitating digestion.

  • Processes:

    • Churning contents to mix with digestive juices and enhance absorption contact.

    • Propelling food along the alimentary tract; eliminating waste.

    • Mastication: Chewing to reduce food particle size and mix with saliva.

Page 4: Phases of Swallowing (Deglutition)

  • Oral Stage: Voluntary control; forms bolus on the tongue, pushed to the oropharynx.

  • Pharyngeal Stage: Involuntary; blocks oral cavity and nasopharynx to propel bolus to esophagus.

  • Esophageal Stage: Involuntary; movements push the bolus into the stomach.

Page 5: Types of Motility

  • Peristalsis: Wavelike muscle contractions that move food forward in the GI tract.

  • Segmentation: Mixing movements that facilitate digestion and absorption by bringing contents in contact with intestinal mucosa.

Page 6: Regulation of Motility

  • Gastric Motility: Detailed processes of stomach emptying, influenced by hormonal and nervous signals.

    • Takes approximately 2 to 6 hours. Chyme ejected every 20 seconds.

    • Hormonal Mechanism: Fats in duodenum release gastric inhibitory peptide, slowing gastric peristalsis.

    • Nervous Mechanism: Enterogastric reflex inhibits gastric peristalsis based on acid presence and distention.

  • Intestinal Motility: Includes peristalsis and segmentation; timing of peristalsis increases as chyme approaches the large intestine.