LEC 21: DIGESTIVE SYSTEM

• ingestion


  Taking food into the gastrointestinal tract
• secretion


  Releasing digestive enzymes and other substances to aid in digestion
• motility 


  1. Movement of food along the digestive tract through processes like peristalsis and segmentation

  2. Mechanical breakdown to increase surface area for digestion

  3. Mixing food with digestive enzyme secretions

  4. Chewing food with saliva

  5. Churning food in the stomach

  6. Segmentation, which is mixing food with digestive juices in the intestines
• digestion


  Breakdown of food into smaller, absorbable molecules by enzymes
• absorption


  Movement of digested nutrients from the digestive tract into the bloodstream or lymphatic system
• defecation


  Elimination of indigestible water products from the body through the anus
• mucosa


  • Innermost layer of the alimentary canal
  • Lines the entire digestive tract
  • Always in contact with food
  • Functions: Secretion of gastrointestinal juices, Absorption of digested end products, Protection against infectious disease
• submucosa


  • Beneath the mucosa
  • Monitor and control layers
  • Contains blood and lymphatic vessels, lymphoid follicles, nerve fibers
  • Functions: Provides support to the mucosa, Allows passage of blood and lymphatic vessels
• muscularis


  • Beneath submucosa
  • Functions: Performs peristalsis, Facilitates segmentation of food
• serosa


  • Protective outermost layer
  • Forms visceral peritoneum
  • Functions: Protection, Supports digestive organs
• splanchnic circulation


  Arteries from abdominal aorta supply blood to digestive organs
• hepatic portal system

  • Collects nutrient-rich blood from digestive organs and delivers it to liver for processing
  • Importance: Allows liver to regulate nutrient levels in bloodstream before blood enters general circulation
• PERITONEUM

  • Location: Lines abdominal cavity (parietal peritoneum) and covers the organs (visceral peritoneum)
  • Functions: Provides support and protection for the abdominal organs, Allows them to move freely within the cavity, Secretes lubricating fluid to reduce friction
• Peritoneal cavity


  Filled with serous fluid to allow organs to move near each other without friction causing damage to the tissues
• Mesentery


  Extends to the digestive organs from body wall, Allows blood vessels, lymphatics, and nerves to reach the digestive organs, Holds the organs in place and stores fat
• Greater omentum


  Hangs from the greater curve of the stomach in front of the intestines
• Lesser omentum


  Hangs from the liver to the lesser curve of the stomach
• retroperitoneal


  • Refers to organs located posterior to the peritoneum, against the dorsal abdominal wall
  • Organs: Most of the pancreas, Duodenum, Parts of the large intestine
• EFFECTORS OF DIGESTIVE SYSTEM

  Smooth muscle and glands in the GI system respond to stimuli
• enteric nervous system

  • Participates in both short and long reflexes
  • short reflexes: mediated entirely by enteric neurons
  • long reflexes: involves CNS integration centres and extrinsic autonomic nerves
• chemical stimuli 


  Presence of food molecules, certain nutrients and pH changes
• mechanical stimuli


  Physical stretching or movement of the GI tract