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The Small Intestine and Digestion Q: Breaking down of carbohydrates (sugar) begins where? – in your mouth (enzyme: salivary amylase in saliva) Q: Breaking down of proteins begins where? – in your stomach (enzyme: pepsin) • but, resulting molecules are still too large for your cells to absorb and use!!! • so, proteins, fats and sugars must be further mechanically and chemically digested in your small intestine 4) Small intestine: a tube 2.5 cm in diameter and 4-6 m long! mouth esophagus stomach small intestine large intestine The Small Intestine (SI) • The small intestine is attached to the stomach and is divided into three sections: 1) The duodenum (connected to the stomach) 2) The jejunum (middle portion) 3) The ileum (connected to the large intestine) 5) Liver (organ): - Is the largest organ in the human body - Produces 1L of bile each day Bile - Green fluid produced by the liver and stored in the gall bladder - Breaks up (emulsifies) fat particles in the SI 6) Gall bladder (organ) - Stores bile and releases it into the duodenum (SI) when necessary 7) Pancreas (organ): - Secretes 1.3 L of pancreatic juices into the SI each day - Secretes insulin (hormone that breaks down sugar) Digestion of Food in the SI • When food enters the small intestine three substances are secreted into it: 1) Bile secreted by the gall bladder (but produced in the liver) Bile aids in the mechanical digestion of fats. 2) Intestinal juices secreted by glands that line the walls of the small intestine 3) Pancreatic juices secreted by the pancreas These 2 juices contain enzymes that complete the chemical digestion of carbohydrates, proteins and fats in the SI Mechanical Digestion in the SI • Food is also churned in the SI just like in the stomach – This is necessary to mix the chyme with the digestive juices of the SI • Food advances throughout the SI through peristalsis just like in the esophagus Digestion of Fat in the SI • The chyme that leaves your stomach and enters the SI contains water and fat. • Water and fat do not mix, they coalesce – This means the fat floats to the surface of the water • Bile is required to separate the fat molecules from the water molecules. – This is called emulsification • Emulsified fat molecules have only been mechanically digested as bile does not contain enzymes and only separates molecules from each other. • Emulsified fat molecules then mix with digestive juices (in the SI) containing enzymes which digest the fat chemically. Practice Questions 1) What are the names of the 3 sections of the small intestine? 2) How is the inner lining of the small intestine special and why is this important to digestion? 3) What three substances does the small intestine contain and which organs or cells are responsible for secreting each of these substances? 4) What 3 nutrients are digested in the small intestine and what are the names of their individual components? 5) What is the function of bile, where is it produced and where is it stored? 6) What hormone does the pancreas produce? 7) What process does the stomach and the small intestine have in common? What about the esophagus and the small intestine?