SCIENCE - Digestive System

• Ingestion


  Entry of food into the alimentary canal through the mouth
• Chewing


  Food is chewed and mixed with saliva, which contains enzymes that begin breaking down the carbohydrates in the food plus some lipid digestion via lingual lipase
• Bolus


  Appropriately sized food after chewing
• Swallowing


  Food leaves the mouth when the tongue and pharyngeal muscles propel it into the esophagus
• Propulsion


  Movement of food through the digestive tract
• Peristalsis


  Sequential, alternating waves of contraction and relaxation of alimentary wall smooth muscles, which act to propel food along
• Peristalsis is so powerful that foods and liquids you swallow enter your stomach even if you are standing on your head
• Mechanical digestion


  A purely physical process that does not change the chemical nature of the food, but makes the food smaller to increase both surface area and mobility
• Mechanical digestion


  1. Mastication (chewing)

  2. Tongue movements that help break food into smaller bits and mix food with saliva

  3. Churning of food in the stomach to further break it apart and expose more of its surface area to digestive juices
• Chyme

  Acidic "soup" created by mechanical churning of food in the stomach
• Segmentation


  Localized contractions of circular muscle of the muscularis layer of the alimentary canal, isolating small sections of the intestine and moving their contents back and forth while continuously subdividing, breaking up, and mixing the contents
• Chemical digestion


  Digestive secretions break down complex food molecules into their chemical building blocks (e.g. proteins into amino acids)
• Absorption


  1. Nutrients from broken down food enter the bloodstream through the epithelial cells that make up the mucosa of the small intestine

  2. Lipids are absorbed into lacteals and transported via the lymphatic vessels to the bloodstream
• Defecation


  Undigested materials are removed from the body as feces