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The Digestive System

The Digestive System. Food, Glorious Food!. Functions. Take in food  ingestion Physical & chemical break down of food  digestion Absorption of nutrients Excretes waste  defecates. Two Main Groups . Alimentary Canal (AKA GI tract )

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The Digestive System

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  1. The Digestive System Food, Glorious Food!

  2. Functions • Take in food  ingestion • Physical & chemical break down of food  digestion • Absorption of nutrients • Excretes waste  defecates

  3. Two Main Groups • Alimentary Canal (AKA GI tract) • Coiled, hollow muscular tube food travels through in body • Performs all 4 digestive functions • Open on both ends  outside of body 2) Accessory organs – help digest, but don’t digest directly (never touch food) "The GI tract extends from the mouth to the anus, is a continuous tube about 30 ft long." Van De Graaf, Kent. Human Anatomy. McGraw-Hill. 2000.

  4. Mouth • Food enters the mouth (oral cavity) • Enzymes in your saliva (salivary amylase) begin digestion of starches • Tongue- muscle on floor of mouth, helps mix food and saliva; taste • Lingual frenulum– holds tongue to floor • Uvula – tissue at posterior soft palate; gag reflex • Masticate- chew

  5. Pharynx (pg 473 Fig 14.3) • Walls contain 2 layers of skeletal muscle • Inner muscle layer  longitudinal • Outer muscle layer  run circularly • Layers alternate contractions to move food in a wave-like fashion (peristalsis) https://www.youtube.com/watch?v=-LJVTBuiPgQ

  6. Esophagus (pg 473 Fig 14.3) • Connects pharynx – stomach (passes through the diaphragm) • Has 4 tissue layers

  7. Has 4 tissue layers: • 1. Mucosa- moist, inner-most, around lumen • 2. Submucosa- connective tissue, bl vessels, nerves, etc. • 3. Muscularis- (2 layers) inner circular and outer longitudinal • 4. Serosa- visceral and parietal peritoneum

  8. Stomach • C-shaped; has 3 muscular layers to move & mix food • Has sphincters (cardioesophageal & pyloric) to prevent unregulated movement of food and gastric juices out of stomach

  9. Stomach • Expands and collapses based on food content • Can hold about 1 gallon of food full, 50 mL when empty • When collapsed mucosa layer make large folds (rugae) rugae

  10. Lesser omentum- • Connects liver to “inside” curve of stomach • Greater omentum- • Connects large curve of stomach to the intestines Both are… • Extensions of visceral peritoneum • Riddled with fat to insulate, & protect internal organs • Have many lymph nodes https://www.youtube.com/watch?v=SKP1q-xpooo start at 26 sec

  11. Digestion Continues in the Stomach • Mucosa produces alkaline mucus that coats the stomach  why? • Mucosa has lots of deep gastric pits • Where gastric juices are produced

  12. Gastric Pit Excretions • Chief cells (in gastric pit) make enzymes the break down proteins • pepsinogenbefore it’s activated, pepsin when activated)  breakdown of proteins begins here • Parietal cells (in gastric pit) produce: • HCl- makes stomach acidic  activates enzymes • Intrinsic factor – allows absorption of vitamin B12 in small intestine

  13. Gastric Pit Excretions • Most digestion in stomach occurs in pyloric region • After being processed and churned in the stomach food = chyme • To leave stomach chyme passes through the pyloric sphincter https://www.youtube.com/watch?v=YJ34Qx6hzJk

  14. Peptic Ulcers • Hole in the wall of the: • Stomach • Esophagus • Small intestine (upper section) • NOT caused by stress & spicy foods  a bacteria • Symptoms: • Pain navel-chest • Blood in vomit or stool • Temp. relief w/ antacids • Pain comes & goes

  15. Small Intestine • Major digestive organ • almost all food absorption occurs here • Goes from pyloric sphincter (in stomach) to small intestine • Longest part of GI tract • 8 - 20 feet long

  16. Parts of the Small Intestine • Duodenum(~5% length) • LOTS of enzyme activity • Place where pancreatic and bile ducts empty their chemicals; like a “car wash” • Jejunum (~40% length) • Ileum(~60% length) • Both absorb nutrients

  17. Structure of the Small Intestine **Structure of the small intestine is key to absorption – increase surface area to increase rate of absorption** • Villi – fingerlike projections (each has microvilli on it) • Microvilli – tiny projections of mucosa cells; make the Brush border • Lacteal – lymphatic capillary in each villus

  18. Large Intestine • Major functions: • Dry out indigestible food • Eliminate waste as feces • Produce alkaline mucus • Absorb nutrients produced by bacteria in colon • No villi

  19. Large Intestine

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