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Introduction to the Digestive System

Introduction to the Digestive System. For student copy. Digestive system & homeostasis. Digestive system contributes to homeostasis of body by breaking down food into forms that can be absorbed & used by body cells. also: absorbs : water, vitamins, minerals eliminates: wastes.

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Introduction to the Digestive System

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  1. Introduction to the Digestive System For student copy

  2. Digestive system & homeostasis • Digestive system contributes to homeostasis of body by breaking down food into forms that can be absorbed & used by body cells. • also: • absorbs : • water, vitamins, minerals • eliminates: • wastes

  3. Accessory Organs 2 groups of organs: GI Tract aka Alimentary Canal continuous tube mouth  anus mouth most of pharynx esophagus stomach small & large intestine teeth tongue salivary glands liver gallbladder pancreas

  4. vocabulary • Ingestion: eating • Secretion: ~7 liters water, acids, buffers, & enzymes into lumen of GI tract • Motility: contraction/relaxation of smooth muscle in wall of GI tract mix & propel food & secretions  anus • Mechanical Digestion: physically breaking down food • Chemical Digestion: • Absorption • Defecation: wastes leave body/ material defecated called feces/ gas called flatus

  5. Layers of the gi tract (inner  outer) • mucosa • submucosa • muscularis • serosa

  6. Mucosa: 3 layers • epithelium • mouth  esophagus: stratified sq. epith for protection • stomach  intestines: simple columnar • cells slough off q 5-7 d • exocrine mucus glands (mucus & water) & several types endocrine glands called enteroendocrinecells interspersed

  7. Mucosa: 2nd layer:lamina propia • areolar CT • rich in blood & lymph vessels • contains most of MALT (mucosa-associated lymphatic tissue)

  8. Mucosa: 3rd layer:muscularis mucosa • thin layer of smooth muscle • creates small folds in epithelium  increases surface area for digestion & absorption

  9. submucosa • areolar CT that binds mucosa to muscularis • rich blood & lymphatics, glands • submucosal plexus: extensive network of neurons

  10. Muscularis • skeletal muscle in mouth, pharynx, superior & middle parts of esophagus, external anal sphincter • voluntary swallowing & defecation • 2 sheets smooth muscle in rest of GI tract with myenteric plexus between them • outer longitudinal • inner circular

  11. Serosa • parts of GI tract suspended in abdominopelvic cavity have this superficial layer = visceral peritoneum • esophagus lacks a serosa; has adventitia a single layer of areolar CT

  12. Innervation of thegi tract

  13. Enteric Nervous System(ENS) • 100 million neurons that extends from esophagus  anus • 2 plexuses: • myenteric plexus (plexus of Auerbach) • motor neurons of longitudinal & circular muscle • submucosal plexus (plexus of Meissner) • w/in submucosa supplying the secretory cells

  14. ANS • parasympathetic fibers via X to most of GI tract (not to 2nd ½ large intestine: gets it from sacral spinal cord) • increase secretions & motility • sympathetic fibers from thoracic & upper lumbar spinal nerves • decrease secretions & motility

  15. Peritoneum • largest serous membrane of body • simple squamous epithelium with underlying areolar CT • divided: • parietal peritoneum • visceral peritoneum

  16. Peritoneal Cavity • space between parietal & visceral peritoneums • contains serous fluid: decreases friction • Ascites: excess serous fluid ass’c w/ some diseases

  17. Retroperitoneal • “behind peritoneum” • kidneys & most of pancreas, end of sigmoid colon under parietal peritoneum

  18. 5 Major Peritoneal Folds • greater omentum • falciform ligament • lesser omentum • mesentery • mesocolon

  19. Greater Omentum • largest peritoneal fold • “fatty apron” • drapes over transverse colon & coils of sm intestine • extends downward anterior to sm intestine • contains adipose cells, macrophages, plasma cells; • function to combat & contain infections

  20. Greater omentum

  21. FalciformLigament • attaches liver to anterior abdominal wall & diaphragm • liver only organ in abdominopelvic cavity attached to anterior abd wall

  22. Lesser Omentum • arises as 2 folds in serosa of stomach & duodenum

  23. Mesentery • fold of peritoneum that attaches small intestine to posterior abdominal wall • starts @ posterior wall  wraps around sm intestine  reflects back to posterior abd wall • route of bld supply to sm intestine

  24. Mesocolon • binds large intestine to posterior abd wall • route of blood supply, lymphatic drainage

  25. Peritonitis • acute inflammation of the peritoneum: contamination by infectious microbes • from punctures of abdominal organs • trauma • surgical wounds

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