Digestive system

• 
  

  The order of the digestive process.

  1. Ingestion

  2. Absorption

  3. Assimilation

  4. Excretion
• The digestive system is a continuous tube that begins at the mouth and ends at the anus

  
• The digestive system is about 30 feet long in the average adult, and is known as the alimentary canal or gastrointestinal tract
• Functions of the digestive system

  • Digestion of food into nutrients
  • Absorption of nutrients into the bloodstream
  • Elimination of solid wastes

  
• Mechanical and chemical digestion

  1. Mechanical digestion: Physical breakdown of large pieces of food into smaller pieces

  2. Chemical digestion: Food is broken down by digestive enzymes

  
• Saliva


  A watery fluid produced by the salivary glands and delivered to the mouth
• Salivary glands


  • Three pairs of glands (parotid, sublingual, and submandibular) that open into the oral cavity and produce saliva

  
• Sensory organs send message to brain


  Brain sends message to salivary glands to secrete chemicals to begin digestive process
• Tongue


  • A muscle covered with a mucous membrane, with a rear portion called the root, the tip, and the central body, covered with taste buds and papillae

  
• Teeth


  • Used for chewing food (mastication), breaking it apart and mixing it with saliva to form a bolus
• Swallowing


  Muscular constrictions move the bolus through the pharynx and into the esophagus, while blocking the opening to the larynx

  
• Esophagus


  • Food is moved down the esophagus toward the stomach by wavelike muscular contractions called peristalsis

  
• Lower esophageal sphincter


  • A muscle valve that permits the passage of food into the stomach, but not the backup of stomach contents under normal conditions

  
• The muscles of the small intestine mix food with digestive juices from the pancreas, liver, and intestine and push the mixture forward to help with further digestion

  
• The walls of the small intestine absorb the digested nutrients into the bloodstream, and the blood delivers the nutrients to the rest of the body

  
• Stomach


  • A muscular, expandable organ with an upper portion called the fundus and a lower portion called the antrum, where hydrochloric acid and other gastric juices convert food to a semiliquid state called chyme
• Chyme passing through the pyloric sphincter valve


  Chyme passes from the stomach into the small intestine
• Small intestine


  • About 21 feet long and 1 inch in diameter, extending from the pyloric sphincter valve to the large intestine, with the duodenum, jejunum, and ileum sections
• Liver


  • Produces bile or gall, which drains into the duodenum and helps digest fats, also stores iron and fat-soluble vitamins
• Gallbladder


  • Stores and concentrates bile, which is then discharged into the duodenum when chyme containing fat leaves the stomach
• Pancreas


  • Secretes pancreatic juice into the duodenum via the pancreatic duct, containing digestive enzymes and bicarbonate ions
• Jejunum and ileum


  • Lined with hair-like protrusions called villi that slow the passage of food and allow nutrients to be absorbed into the bloodstream

  
• Excretion


  The process of expelling waste matter from the body, such as urine or sweat
• Large intestine


  • Absorbs remaining water and nutrients from indigestible food matter, stores unusable food matter (wastes), and eliminates the wastes from the body
• Rectum and anus


  • The rectum stores feces until they are expelled through the anus during a bowel movement, with the external anal sphincter muscle consciously relaxed to allow defecation
• Water is the most important nutrient, as every cell in the human body needs water and many body processes and chemical reactions take place in water
• The function of the digestive system is to help convert large food molecules into simpler molecules (monomers) that can be absorbed and used by the cells of the body

  
• Drink at least 1-2 liters of water each day (6-8 cups), as not enough water can lead to dehydration and problems in the circulatory, respiratory, and nervous systems