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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 1) 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 "The GI tract extends from the mouth to the body anus, is a continuous tube about 30 ft long." 2) Accessory organs – help digest, but don’t digest directly (never touch food) Van De Graaf, Kent. Human Anatomy. McGraw-Hill. 2000. 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 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 Esophagus (pg 473 Fig 14.3) • Connects pharynx – stomach (passes through the diaphragm) • Has 4 tissue layers Has 4 tissue layers: 1. Mucosa- moist, inner-most, around lumen 2. Submucosaconnective tissue, bl vessels, nerves, etc. 3. Muscularis- (2 layers) inner circular and outer longitudinal 4. Serosa- visceral and parietal peritoneum 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 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 • 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 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 Gastric Pit• Excretions Chief cells (in gastric pit) make enzymes the break down proteins – pepsinogen before 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 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 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 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 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 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 Large Intestine • Major functions: – Dry out indigestible food – Eliminate waste as feces – Produce alkaline mucus – Absorb nutrients produced by bacteria in colon • No villi Large Intestine