Science8-quarter4: Digestive System

• Digestion


  Function of Digestive system - breaks down food mechanically and chemically
• Journey of food


  1. Starts from the mouth down to the anus

  2. Takes about 18-20 hours
• Ingestion


  Taking in food or any substance into the body through the mouth
• Digestion


  Process involves break down of large food molecules into smaller molecules for easy absorption by the cells
• Mastication/Chewing


  Process when food is in the mouth, teeth cut, crush, and break it apart into tiny pieces, the tongue helps mix food with saliva forming a moist ball called bolus
• Mechanical digestion


  The initial stage
• Salivary amylase


  Enzyme that breaks down starch into smaller carbohydrates
• Esophagus


  1. Tube that attaches the mouth to the stomach

  2. Bolus passes from the mouth to the esophagus
• Peristalsis


  Series of wave-like muscle contractions that push and transport foods and liquids in small sections to the stomach
• Stomach


  • J-shaped, bag-like muscular organ that can hold approximately one liter of fluid
  • Primary function is to store food, which turns to chyme after being acted on by the stomach acid
• Chyme


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


  • Have special cells that secrete gastric juices like hydrochloric acid and pepsin that begin the chemical breakdown of proteins
• Three organs that are part of the digestive system and help in secretion of essential substances

  • Liver
  • Gallbladder
  • Pancreas
• Liver


  • Produces bile, a green fluid that turns large fat droplets into smaller ones and stores them in the gallbladder
  • Bile gets into the small intestine and helps in the digestion of fat
• Pancreas


  • Makes three different kinds of enzymes: amylase, peptidase, and lipase released through a pancreatic duct that aid in the digestion of carbohydrates, proteins, and fats
  • Produces about half a liter of digestive juices each day
• Gallbladder


  Small pear-shaped sac that can hold about 50 ml of bile
• Small intestine


  1. Organ that breaks down food further into substances, such as glucose, that can be absorbed by the villi and ileum

  2. Has 3 parts: duodenum, jejunum, and ileum
• Duodenum


  • First and shortest part of small intestine that starts at the lower end of the stomach and extends about 20-25 cm in length
  • In charge for the continuous breaking-down process as it partially receives the chyme from the stomach, it resumes chemical digestion of food and prepares absorption through the villi
• Carbohydrates


  Broken down into sugars by enzymes like amylase, maltase, and lactase
• Proteins


  Broken down into amino acids by enzymes like trypsin and peptidase
• Fats


  Broken down into fatty acids by the enzyme lipase
• Secretion


  • Production and release of enzymes and acids in the digestive system
  • Aids in the breaking down of complex food molecules into their chemical building blocks
• Jejunum


  • Second part of small intestine, 2.5 cm in length
  • Its wall works for absorption through enterocytes or columnar cells of small nutrient particles which have been previously digested by the enzymes in the duodenum
• Villi


  • Tiny, finger-like projections from the epithelial lining of the intestinal wall
  • Each villus contains blood capillaries that enable it to absorb water, glucose, amino acids, vitamins, minerals, and fatty acids
  • Increases the amount of surface area available for the absorption of nutrients
• 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 serve to expand the surface area for diffusion and also to lessen any increase in volume
• Ileum


  • Third part of small intestine, 8.5 m in length
  • Main function is to assimilation (absorption) of B12 and the re-assimilation (reabsorption) of conjugated bile salts
• Large Intestine


  • Divided into caecum, ascending colon, transverse colon, descending colon, and sigmoid colon
  • Reabsorption of liquid electrolytes and some vitamins from the undigested food takes place
  • Secretes mucus to aid in the formation of feces and maintains alkaline conditions
  • Last segment of the gastrointestinal tract that completes absorption and compacts waste
• Egestion


  Release of undigested food collected in the rectum called feces and pushed out of the body through the anus by defecation
• Absorption


  1. Third process
  2. Occurs mostly in the small intestine, where several digestive juices, pancreatic juice, and bile aid in the chemical digestion of food
  3. Process of passing the soluble food molecules in the wall of the small intestine through the villi