Digestive Processes 1 - 2.26.25

Page 1: Introduction to Digestive Processes

• Title: Mouth and Stomach

• Course: Anatomy and Physiology

• Date: Spring 2025, Wednesday, February 26

Page 2: Stages of the Digestive Process

• Ingestion: Taking in food.

• Digestion: Breakdown of food into smaller components.

  • Mechanical Digestion: Involves teeth, stomach, and intestines.

  • Chemical Digestion: Breakdown by digestive enzymes.

• Absorption: Uptake of nutrient molecules into the bloodstream.

• Compaction: Consolidation of feces.

• Defecation: Elimination of waste.

Page 3: Mastication

• Definition: Mechanical processing of ingested food.

• Purpose: Facilitate swallowing and increase surface area for digestion.

• Characteristics:

  • Partially voluntary and reflexive process.

  • Structures involved:

    • Lips & Cheeks: Retain food inside the mouth.

    • Teeth: Cut and grind food.

    • Tongue: Manipulates food, forming a bolus.

• Muscles of Mastication:

  • Masseter & Temporalis: Elevate the jaw.

  • Pterygoids: Lateral movement of the jaw.

Page 4: Salivation

• Regulation by salivary nuclei in the brainstem.

• Stimuli: Mechanoreceptors and chemoreceptors in the oral cavity.

  • Anticipation of food can trigger salivation.

• Autonomic Nervous System controls:

  • Parasympathetic: Stimulates salivation.

  • Sympathetic: Inhibits salivation.

Page 5: Swallowing (Oral Phase)

• Muscle activity coordinated by the swallowing center in the medulla oblongata.

• Oral Phase: Voluntary control.

  • Tongue forms bolus and pushes it posteriorly for swallowing.

Page 6: Swallowing (Pharyngeal Phase)

• Involuntary reflex begins here.

• Mechanisms to prevent backflow:

  • Soft palate and root of tongue raise to block nasal passage.

  • Bolus tips the epiglottis, closing the trachea.

  • Pharyngeal constrictor muscles drive the bolus downward.

• Respiratory Protections:

  • Breathing is automatically suspended.

  • Larynx is elevated by extrinsic muscles.

  • Vestibular folds close to prevent air entry.

Page 7: Esophagus and Esophageal Phase

• Esophageal Phase: Involuntary movement of food.

  • Peristalsis transports the bolus.

  • Lower Esophageal Sphincter: Relaxes to allow food into the stomach.

Page 8: Regulation of Digestive Activity

• Hormonal influences from gastric and intestinal enteroendocrine cells.

• Role of Central Nervous System (CNS):

  • Enteric Nervous System: Main control source for digestive functions.

  • Composed of over 100 million neurons, can function independently of CNS.

Page 9: Enteric Nervous Networks

• Submucosal Plexus: Regulates gland activity.

• Myenteric Plexus: Regulates smooth muscle contractions in digestive tract.

Page 10: Neural Regulation of Digestion

• Short (Myenteric) Reflexes: Intrinsic control via local stimuli in digestive tract.

• Long (Vagovagal) Reflexes: Extrinsic control involving CNS autonomics. Can be triggered by both internal and external stimuli.

Page 11: Gastric Motility

• Sensory stimuli from pharyngeal mechanoreceptors relay to swallowing center.

• Receptive Relaxation: Parasympathetic stimulation via vagus nerves prepares stomach for food.

• Antral Pump: Strong contractions help prepare food for duodenum, controlling pyloric sphincter.

Page 12: Gastric Motility Continued

• Approximately 3mL of chyme enters the duodenum at a time.

• Relaxation of the stomach allows sphincter to open for gradual chyme release.

• Duodenum Overfilling: Inhibits gastric motility.

• Typical stomach emptying: Around 4 hours.

Page 13: Vomiting

• Controlled by the emetic center in the medulla oblongata.

• Triggering factors include:

  • Overstretching of stomach/duodenum.

  • Chemical irritants.

  • Viscera trauma or intense pain.

  • Psychological or sensory stimuli.

• Process involves relaxation of lower esophageal sphincter and intense abdominal contractions.

Page 14: Digestion and Absorption in the Stomach

• Mechanical and chemical digestion occurs through:

  • Churning from peristaltic contractions.

  • Action of gastric enzymes and HCl.

• Absorption: Very minimal nutrients absorbed in the stomach.

Page 15: Regulation of Gastric Function

• Activities increase after food intake; decrease as stomach empties.

• Phases based on site of control:

  • Cephalic Phase: Brain response to food anticipation.

  • Gastric Phase: Local response in stomach.

  • Intestinal Phase: Response in small intestine.

• Overlapping phases that can occur simultaneously.

Page 16: Cephalic Phase

• Stimulatory Events:

  • Anticipation related to the sight and thought of food,

  • Taste and smell stimulation.

  • Increased secretion of HCl via vagus nerve stimulation.

• Inhibitory Events:

  • Emotional states reducing parasympathetic activity.

  • Sympathetic stimulation can override parasympathetic effects.

Page 17: Gastric Phase

• Stimulatory Factors:

  • Activation from swallowed food and stomach distension increases pH.

  • Stimulates secretion of HCl and intrinsic factor via long and short reflexes.

• Inhibitory Factors:

  • Excessive acidity decreases gastric secretions.

Page 18: Intestinal Phase

• Primarily inhibitory phase:

  • Pyloric sphincter restricts chyme entry into the duodenum.

  • Intestinal hormones decrease gastric activity via enterogastric reflex triggered by chyme acidity and fats.

  • Signals inhibit gastric activity both locally and from CNS.

  • Hormones stimulate bile release from the liver and insulin from the pancreas.

Page 19: Flowchart of Digestive Phases

• Cephalic Phase Events:

  • 1a: Sight and thought of food activate brain centers.

  • 1b: Taste and smell receptor stimulation.

  • 2a: Stomach distension activates long and short reflexes.

  • 2b: Food chemicals increase gastric activity.

• Intestinal Phase Events:

  • 3a: Presence of food in the duodenum stimulates further digestive secretions.

• Inhibitory Signals:

  • Loss of appetite, depression affects appetite stimulation.

  • Excessive acidity inhibits gastric activity.