biol_1322_ch3

biol_1322_ch3 - Digestion, Absorption and Transport Chapter...

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1 Digestion, Absorption and Transport Chapter 3 Organization of the GI Tract • Mouth --> Esophagus --> Stomach --> Small Intestine --> Large Intestine --> Anus • GI Tract works with assisting organs: – salivary glands –l iver – gallbladder –pancreas Sphincters of the GI Tract • Cardiac (lower esophageal sphincter) - located between the esophagus and the stomach. Prevents food from refluxing back into the esophagus • Pyloric sphincter - located between the stomach and duodenum • Ileocecal - located between the ileum and ascending colon • Rectum/anal opening How Does the Body Process Food? • The action unfolds in the GI Tract in two ways: – Digestion - the process of transforming the foods we eat into units for absorption – Absorption - the movement of these small units from the gut into the bloodstream or lymphatic system for circulation • The digestive system is designed to digest carbohydrates, proteins, and fat simultaneously, while preparing other substances - vitamins, minerals, and cholesterol - for absorption What is the Goal? • During digestion, the body’s goal is to break down large, complex nutrients into their simplest form •Fa t s Æ 2 free fatty acids and one monoglyceride •P ro te in s Æ free amino acids •S ta
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2 Mechanical Digestion in the Mouth • Mechanical digestion is taking place - mixing and churning of food substances • Saliva, mucus, and other fluids mix with the food so that it is easier to swallow • Masticated food is now called a “bolus” • Bolus must slide over the epiglottis, which blocks the entrance to the lungs Salivary Glands •Sa l iva –Water, salts, mucus, enzymes Enzymatic Digestion in the Mouth • Salivary glands secrete saliva and salivary amylase • Salivary amylase begins to breakdown carbohydrate (starch) into dextrins – the longer the carbohydrates stay in the mouth, the more digestion takes place - cracker becomes “sweeter” b/c it is broken down into sugars •Very small amount of lingual lipase is secreted and begins fat digestion In the Stomach…. • Bolus slides down the esophagus to the stomach • Once the bolus enters the stomach, gastric juices are secreted –Water & Mucus – Gastrin - triggers HCl acid production –HC l ac id • lowers stomach pH to ~1.5-1.7 (kills antigens) • denatures protein • converts Pepsinogen into Pepsin (protein- digesting enzyme) – Gastric Lipase - breaks down fats – Intrinsic factor is secreted and binds to Vit. B 12 - assists in the absorption of this vitamin in the
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biol_1322_ch3 - Digestion, Absorption and Transport Chapter...

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