DIGESTIVE SYSTEM

• Digestive system


  Made up of the gastrointestinal (GI) tract, liver, pancreas, and gallbladder

  
• GI tract


  • A series of hollow organs joined in a long, twisting tube from the mouth to the anus
• Hollow organs of the GI tract

  • Mouth
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
  • Rectum
  • Anus
• Solid organs of the digestive system

  • Liver
  • Pancreas
  • Gallbladder
• Bacteria in the GI tract, also called gut flora or microbiome, help with digestion
• Parts of the nervous and circulatory systems also play roles in the digestive process
• Digestion


  Breaking down food into nutrients, which the body uses for energy, growth, and cell repair
• Carbohydrates


  Sugars, starches, and fiber found in many foods
• Simple carbohydrates


  Sugars found naturally in foods such as fruits, vegetables, milk, and milk products, as well as sugars added during food processing
• Complex carbohydrates


  Starches and fiber found in whole-grain breads and cereals, starchy vegetables, and legumes
• The Dietary Guidelines for Americans, 2010, recommends that 45 to 65 percent of total daily calories come from carbohydrates
• Protein


  Large molecules that the body digests into smaller molecules called amino acids
• The Dietary Guidelines for Americans, 2010, recommends that 10 to 35 percent of total daily calories come from protein
• Fats


  A rich source of energy for the body that help the body absorb vitamins
• The Dietary Guidelines for Americans, 2010, recommends that 20 to 35 percent of total daily calories come from fat
• Water-soluble vitamins


  Include all the B vitamins and vitamin C
• Fat-soluble vitamins


  Include vitamins A, D, E, and K
• The body stores fat-soluble vitamins in the liver and fatty tissues, whereas the body does not easily store water-soluble vitamins and flushes out the extra in the urine
• Digestion


  1. Begins in the mouth with chewing and ends in the small intestine

  2. Food mixes with digestive juices, causing large molecules to break down into smaller molecules

  3. Smaller molecules are absorbed through the walls of the small intestine into the bloodstream

  4. Waste products pass through the large intestine and out of the body as stool
• Parts of the digestive process performed by each organ

  • Mouth: Chewing, saliva (breaks down starches)
  • Esophagus: Swallowing (no digestive juices)
  • Stomach: Upper muscle relaxes to let food enter, lower muscle mixes food with stomach acid (breaks down protein)
  • Small intestine: Peristalsis, small intestine digestive juice (breaks down starches, protein, and carbohydrates)
  • Pancreas: Pancreatic juice (breaks down starches, fats, and protein)
  • Liver: Bile (breaks down fats)
• Peristalsis


  The movement of organ walls that propels food and liquid through the GI tract and mixes the contents within each organ
• Lower esophageal sphincter


  A ringlike muscle at the junction of the esophagus and stomach that controls the passage of food and liquid between the esophagus and stomach
• Chyme


  The mixture of food and digestive juices that is slowly emptied from the stomach into the small intestine
• Salivary glands


  Produce saliva that moistens food and contains an enzyme that begins to break down starches
• Glands in the stomach lining

  Produce stomach acid and an enzyme that digests protein
• Pancreatic juice


  Contains enzymes that break down carbohydrates, fats, and proteins
• Bile


  A digestive juice produced by the liver that mixes with and dissolves fats
• The gallbladder stores bile between meals and squeezes it into the small intestine when a person eats
• Pancreas


  • Produces a juice containing enzymes that break down carbohydrates, fats, and proteins
• Liver


  • Produces a digestive juice called bile, which is stored in the gallbladder and released to mix with fat in food
• Small intestine


  • Digestive juice combines with pancreatic juice and bile to complete digestion, absorbing most digested food molecules, water and minerals
• Bacteria in the small intestine

  • Produce some of the enzymes needed to digest carbohydrates
• Digestion


  1. Breaks down food into nutrients

  2. Moves food through the gastrointestinal tract

  3. Begins in the mouth with chewing

  4. Ends in the small intestine

  5. Food mixes with digestive juices to break down large molecules

  6. Smaller molecules are absorbed through the walls of the small intestine into the bloodstream
• Waste products of digestion pass through the large intestine and out of the body as stool
• Digestive juices


  Contain enzymes that break food down into different nutrients
• The small intestine absorbs most digested food molecules, as well as water and minerals, and passes them on to other parts of the body for storage or further chemical change
• Hormone regulators


  • Cells in the lining of the stomach and small intestine produce and release hormones that control the functions of the digestive system, stimulating production of digestive juices and regulating appetite
• Nerve regulators


  • Extrinsic nerves connect the digestive organs to the brain and spinal cord, releasing chemicals to control muscle contractions and relaxation
  • Intrinsic nerves within the GI tract are triggered by food stretching the walls, releasing substances to speed up or delay food movement and digestive juice production
• Digestion is important for breaking down food into nutrients, which the body uses for energy, growth, and cell repair
• The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) conducts and supports research into many kinds of digestive issues, including studies of the basic biology of the digestive system's structure and function