GI anatomy 2

• Gastrointestinal Organs


  • GI Tract
  • Oral cavity
  • Pharynx
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine

  
• Small Intestine Segments


  • Duodenum
  • Jejunum
  • Ileum

  
• Accessory Digestive Organs


  • Liver
  • Gall bladder
  • Pancreas
• Additional Abdominal Organs


  • Kidneys
  • Spleen
• Intestinal Layers


  • Mucosa (contain folds - crypts & villi to increase surface area for digestion/absorption)
  • Submucosa (thin layer - blood vessels, nerves, etc.)
  • Muscularis externa (stomach movement; 2 layers of smooth muscle - circular & longitudinal; no oblique)
  • Serosa (outermost layer - protection and support)

  
• Intestinal Movements


  1. Peristalsis (series of involuntary wave-like muscle contractions to move substance along digestive tract in one direction; coordinated contraction of circular and longitudinal muscle layers)

  2. Segmentation (mixing and churning within smaller segments to facilitate digestion; mainly circular muscle layer)

  
• Jejunum


  Middle portion of small intestine (2 - 3m long); lies in upper and lower left abdominal quadrants; continues absorption of nutrients, fat, and H2O

  
• Ileum


  Third and final segment of small intestine (3 - 4m long, longest segment); most lies in lower right quadrant; mainly H2O and fat absorption, and any remaining nutrients

  
• Large Intestine Segments


  • Cecum
  • Appendix
  • Colon (ascending, transverse, descending, sigmoid)
  • Rectum
  • Anal canal

  
• Large Intestine


  • Teniae coli (three thickened bands of smooth muscle)
  • Haustra (sacs)
  • Omental appendices (small fatty projections)
  • Larger in diameter than small intestine

  
• Cecum


  Large pouch for collection of food; ileum terminates into cecum via ileocecal orifice and valve; no mesentery/mesocolon so can be displaced from iliac fossa
• Appendix


  Vermiform appendix (wormlike, 5 - 10cm); hypothesized to be part of gastrointestinal immune system as a "safe house" for repopulating commensal bacteria after GI illness
• Colon Segments


  • Ascending colon
  • Right colic flexure (hepatic)
  • Transverse colon
  • Left colic flexure (splenic)
  • Descending colon
  • Sigmoid colon
  • Rectum
  • Anal canal
• Large Intestine/Colon


  • Movement of food for elimination
  • H2O and vitamin reabsorption
  • Lined with bacteria to break down any remaining nutrients (i.e. fiber)
  • Chyme moved through, dehydrated, mixed with bacteria and mucus, and formed into feces

  
• Haustral Churning


  1. Haustra remain relaxed and distend as they fill up

  2. After a certain point, the walls contract and squeeze contents into the next haustrum
• Spleen


  Largest lymphatic organ; located in left upper quadrant; organ of odd numbers (dimensions: 1 x 3 x 5 inches, weight: 7 oz.); blood reservoir (5 - 10% of total blood volume)
• Spleen Functions


  • Blood is monitored by T-cells for pathogens
  • Macrophages swallow and digest debris in the blood (i.e. old/damaged red blood cells and platelets)
  • Hematopoiesis during development (process of blood cell formation; bone marrow takes over after maturation of long bones)
• Liver


  Second largest organ of the body (1.5kg); one of two organs able to repair itself; immediately inferior to diaphragm; secretes bile, stores glycogen, produces lymphocytes
• Liver Lobes


  • Left lobe
  • Right lobe
  • Caudate lobe
  • Quadrate lobe
• Primary Intestinal & Liver Arteries

  • Superior mesenteric artery
  • Inferior mesenteric artery
  • Hepatic artery proper
• Primary Intestinal & Liver Veins

  • Superior mesenteric vein
  • Inferior mesenteric vein
  • Splenic vein
  • Hepatic portal vein
• Liver Blood Supply


  • Double blood supply entering porta hepatis: 25% hepatic artery proper (to supply liver organ), 75% hepatic portal vein (from GI tract to be filtered)
• Liver Sinusoids


  Portal vein enters liver and breaks up into capillary network; leakiest capillary bed in the body (fenestrated); hepatic artery and portal veins blood mixes in sinusoids; sinusoids drain into central veins which drain to one hepatic vein to IVC to right atrium
• Portal Triad


  1. Bile duct, 2. Branch of hepatic artery, 3. Branch of hepatic portal vein