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Gut Tube and Digestion

Gut Tube and Digestion. Path of Food Esophagus Stomach Small intestines Large intestines Rectum and anus Liver and Pancreas Digestion function Role in glucose metabolism. Mouth--chewing. Path of Food. Pharynx--conscious swallowing. Esophagusu--transport to stomach.

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Gut Tube and Digestion

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  1. Gut Tube and Digestion • Path of Food • Esophagus • Stomach • Small intestines • Large intestines • Rectum and anus • Liver and Pancreas • Digestion function • Role in glucose metabolism

  2. Mouth--chewing Path of Food Pharynx--conscious swallowing Esophagusu--transport to stomach Stomach--mechanical and chemical breakdown Small Intestines-- chemical digestion and absorption Large Intestines-- resorb water, form feces Rectum---collect and expel feces

  3. Esophagus • Pharynx to stomach • Smooth muscle (conscious swallowing is in pharynx) • Passes through esophageal hiatus in diaphragm, stomach against inferior diaphragm • Cardiac orifice, with esophageal hiatus guard opening to stomach, prevent regurgitation • GERD--gastroesophageal reflux disease • Sometimes due to hiatal hernia • Lower esophagus becomes ulcerous and precancerous • Treat with antacids and other acid-reducing drugs

  4. Stomach • STRUCTURE • J-shaped but varies from “steerhorn” (high and horizontal) to vertically elongate (down to pelvis on tall, thin people) • From esophagus (cardiac orifice) to small intestine (pyloric sphincter) • Greater, lesser curvatures • FUNCTION • Mechanical breakdown of food--smooth muscle in wall • Protein breakdown--pepsin secreted by epithelial lining • Acidic conditions--for pepsin to work and to kill bacteria • Absorption of water, ions and some drugs (e.g., aspirin, alcohol)

  5. Digestive Tract (adult gut tube) Wall • Internal = Mucosa • Epithelium • Lamina propria • Muscularis mucosae • Middle = Submucosa • CT w/ elastic fibers, nerves, vessels • Outer = Muscularis Externa • Inner circular layer • Outer longitudinal layer

  6. Internal Anatomy of Stomach • Mucosa • Rugae: mucosal folds allow expansion • Typical Submucosa • Muscularis externa • Oblique layer • Circular layer • Pyloric sphincter • Longitudinal layer • Serosa pg 648

  7. Small Intestines • Duodenum • C-shaped initial piece (5% of total) • Entries for pancreatic, bile ducts • Jejunum • Fan-shaped coil (40% of total) at superior left abdomen • Ileum • Inferior right part of coil • End of appendix at lower right quadrant

  8. Location of Duodenum

  9. Small Intestine:Modifications for absorption • Length • Increase surface area • Plicae circularis • Transverse ridges of mucosa • Increase surface area • Slow movement of chyme • Villi • Move chyme, increase contact • Contain lacteals: remove fat • Microvilli: • Increase surface area • Modifications decrease distally pg 653

  10. Large Intestines • Frame around rest of gut • Ascending, transverse, descending • Starts at cecum/appendix • Ends at rectum, anal canal • Teniae coli • “ribbons” or strips of muscle along length of colon (three around tube) • Tension in teniae coli forms haustra or sacs • Little continuous movement, but mass peristaltic movement several times daily to force feces towards rectum • Resorption of water from food

  11. Rectum + Anal Canal • Rectum • descends into pelvis • no teniae coli • longitudinal muscle layer complete • rectal valves • Anal Canal (more with pelvis) • passes through levator ani muscle • releases mucus to lubricate feces • Internal anal sphincter • involuntary, smooth m. • External anal sphincter • voluntary, skeletal m. pg 655

  12. Blood supply--ventral branches off of aorta • Celiac a.--to stomach, liver, pancreas, spleen, duodenum • Superior (cranial mesenteric a.--to small intestines and most of colon • Inferior (caudal) mesenteric a.--to descending colon, rectum

  13. Innervation of gut VAGUS • Parasympathetic • What nerve? • Where does it run? • Sympathetic • Only thoracic output from spinal cord • Splanchnic nerves from thorax lateral to vertebral bodies bring posteriorly to abdominal cavity and gut • Synapse in celiac and superior mesenteric ganglia • Both Para- and Sympathetic follow aa. out to organs • High level of local control with network of synapses within ganglia and around gut With aorta

  14. STRUCTURE Large ventral organ of abdominal cavity with multiple lobes (learn them!!) Sets against inferior surface of diaphragm on left side Forms as outpocketing of gut--common bile duct is left as connection Bile duct is two-way street (bile from hepatic duct is stored in gall bladder and later expelled to common bile duct to duodenum) FUNCTION Digestion--bile is digestive enzymes plus RBC breakdown product Removes nutrients and toxins from blood (hepatic portal system brings gut blood directly to liver) Glucose metabolism (with pancreas--see below) Liver

  15. Gallbladder • Muscular sac • Between right + quadrate liver lobes • Bile is stored + concentrated • Bile: breaks down fats = emulsification • Bile • Produced by liver • Stored in gallbladder pg 659

  16. Bile Ducts • Cystic duct • carries bile from gallbladder • Hepatic duct • carries bile from liver • Common Bile duct • joins cystic and hepatic • carries bile into duodenum pg 652

  17. Movement of Bile • Bile secreted by liver continuously • Hepatopancreatic (Vater) ampulla • common bile + main pancreatic duct meet and enter duodenum • Sphincter of Oddi around it • closed when bile not needed for digestion • Bile then backs up into gallbladder via cystic duct • When needed gallbladder contracts, sphincters open pg 652

  18. Liver: External Features • Diaphragmatic surface • Right lobe (larger) • Left lobe • Falciform ligament between • Fissure between • Visceral surface • Quadrate lobe • Caudate lobe • Both part of left lobe pg 659

  19. Liver: Blood Supply • Hepatic Vein • from inferior vena cava • Hepatic Artery • from abdominal aorta • Hepatic Portal Vein • Carries nutrient-rich blood from stomach + intestines to liver • Portal system = 2 capillary beds! pg 660

  20. Hepatic Portal System--concept • Directs blood that has already been through gut capillaries into liver capillaries (or sinusoids) • Allows nutrients and toxins to be removed from blood Fig. 19.22, M&M

  21. Hepatic Portal System--anatomy

  22. Pancreas • STRUCTURE • Smaller, diffuse gland • Head in C of duodenum • Tail extends towards spleen • FUNCTION • Digestion--produces most digestive enzymes • Glucose metabolism--Islets of Langerhans make insulin

  23. Glucose metabolism • Liver receives blood from intestines (don’t forget hepatic portal system • After meal, in response to insulin from pancreas, glucose stored as complex carbohydrate--glycogen--in liver • Between meals, in response to glucagon from pancreas, glucose is released • Pancreas releases insulin when sugar levels in blood go up • Inadequate or zero insulin production results in hyperglycemia or high blood sugar • Overproduction or over-dosing of insulin results in hypoglycemia or low blood sugar--insulin shock • Diabetes is insufficient production of insulin • Type I--juvenile onset with elimination of Islets of langerhans and zero insulin production • Type II--adult onset with gradual loss of insulin production

  24. “How Stuff Works” Diabetes: http://www.howstuffworks.com/diabetes1.htm

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