HUMAN DIGESTIVE SYSTEM

• The human digestive system's function is to digest food, the breakdown of organic compounds into their simple forms (glucose) for use by the cells
• Digestion is the chief function of the digestive system
• The digestive system breaks down food mechanically and chemically
• Ingestion


  Taking in food or any substance into the body through the mouth
• When food is chewed, saliva starts digesting carbohydrates
• Digestion


  Breakdown of large molecules and small molecules for easy absorption of the cells
• Both chemical and mechanical digestion begin immediately in the mouth
• Mastication (chewing)


  • Food in the mouth will crush and break apart into tiny pieces by the teeth
  • The tongue helps mix food with saliva secreted by the salivary glands forming a moist ball called a bolus so it can easily swallow
• Salivary glands


  Three pairs (parotoid, sublingual, and submandibular) that produce saliva containing the enzyme salivary amylase to help break down starch
• Peristalsis


  Wave-like muscle contractions that transport the bolus from the mouth to the stomach

  
• Chyme


  Semifluid material formed from the bolus that is acted upon by the gastric juices secreted by the stomach
• Gastric juices


  Hydrochloric acid and pepsin that begin the chemical breakdown of proteins
• Organs of the digestive system

  • Liver
  • Pancreas
  • Gallbladder

  
• Liver's contribution to digestion

  Production of bile which drains into the duodenum and is stored in the gallbladder
• Gallbladder's function


  Store and secrete bile to help digest fats
• Pancreas


  Produces enzymes (amylase, peptidase, protease, lipase) that aid in the digestion of carbohydrates, proteins, and fats
• Parts of the small intestine

  • Duodenum
  • Jejunum
  • Ileum

  
• Duodenum


  Shortest part of the small intestine, where chemical digestion continues and food is prepared for absorption
• Jejunum


  Second part of the small intestine, where absorption of nutrients occurs through the enterocytes or columnar cells
• Ileum


  Third part of the small intestine, where absorption of B12 and reabsorption of bile salts occurs

  
• Absorption


  Passing of soluble food molecules through the villi in the wall of the small intestine into the blood vessels
• Villi


  Tiny, finger-like projections from the epithelial lining of the intestinal wall that increase the surface area for absorption
• Assimilation


  Movement of digested food nutrients into the blood vessels of the small intestine through diffusion and use of nutrients into the body cells through the microvilli

  
• Microvilli


  Microscopic cellular membrane projections that expand the surface area for diffusion and lessen any increase in volume
• Egestion


  Release of undigested food collected in the rectum (feces) and pushed out of the body through the anus by defecation
• The large intestine is where reabsorption of liquid, electrolytes, and some vitamins from the undigested food takes place