Nutrition in humans

• 1. Salivary amylase
  2. Pharynx
  3. Oesophagus
  4. liver
  5. Gall bladder
  6. Pancreas
  7. Duodenum
  8. Jejunum
  9. Ileum
  10. large intestine
  11. Rectum
  12. Anus

  
• Human digestive system

  1. Cardiac orfice
  2. Stomach
  3. Pyloric sphincter

  
• Functions of digestive system

  1. Ingestion
  2. Transportation
  3. Digestion
  4. Absorption
  5. Assimilation
  6. Secretion
  7. Digestive juices + mucus
  8. Substances useful to the body
  9. Egestion
  10. Passing out of undigested food materials
  11. Only food that is not digested and absorbed
  12. Excretion
  13. Metabolic waste
• Physical digestion

  • Mechanical break up of food molecules into smaller food particles
  • Occurs in the
  • Mouth: Chewing by teeth
  • Stomach: Churning by muscles on stomach walls break up food molecules and mixes them well with the digestive enzymes
  • Increases surface area to volume ratio
• Chemical digestion

  • Breakdown of large food molecules into small soluble food molecules which can be absorbed
  • Hydrolytic reactions catalysed by enzymes
• Absorption

  • Water soluble digested food absorbed into blood capillaries of villi in ileum
  • Digested fats absorbed into villi cells
  • Forms up again to be enter the lacteal
• Human digestive system

  1. Pyloric splinter
  2. Exit of stomach
  3. Controls how much food enters the duodenum
  4. Rectum
  5. Stores waste
  6. Accessory organs
  7. Salivary glands
  8. Secrete saliva
  9. Secrete amylase
  10. Liver
  11. Produces bile
  12. Gall bladder
  13. Stores and secrete bile
  14. Pancreas
  15. Secretes bicarbonate
  16. Secretes enzymes
  17. Trypsin, Amylase, Lipase
  18. Secretes hormones
  19. Insulin, Glucagon
• Peristalsis

  • Enables food to be mix with digestive juices
  • Pushes food down the gut
  • Walls of esophagus
  • Two layered muscles
  • Circular muscles
  • Longitudinal muscles
  • These muscles can be found from esophagus to the gut
  • Muscles are antagonistic
  • When one contracts, other relaxes
  • Causes rhythmic wave like contractions
• Peristalsis

  • Behind the food
  • Circular muscles contracts, longitudinal muscles relax
  • Constricts walls of gut, making it narrower and longer
  • Pushes food forward
  • In front of the food
  • Circular muscles relax, longitudinal muscles contracts
  • Dilates walls of gut, making it wider and shorter
  • Opens up space for food
• Ingestion

  • Food in mouth stimulates salivary glands to secrete saliva
  • Mucin in saliva softens food
  • Salivary amylase in saliva breaks down starch to maltose
  • pH of saliva is neutral
  • Chewing by teeth increases surface area to volume ratio
  • Increases rate of amylase breaking down starch to maltose
• Ingestion

  • Tongue rolls food into boli
  • Boli swallowed and passed down the esophagus via the pharnx
  • Peristalsis in walls of esophagus pushed food down into stomach
  • Gravity also helps
• Ingestion

  • When boli enters stomach, it stimulates gastric glands to secrete gastric juices
  • Peristalsis by the walls of the stomach churns and breaks up the food into smaller particles
  • Also mixes food well with gastric juices
  • Gastric juices consists of hydrochloric acid, pepsin and rennin
• Ingestion

  • In stomach - (Hydrocloric acid)
  • Stops action of salivary amylase by denaturing it
  • Activates inactive forms of enzyme, prorennin and pepsinogen to active forms of enzyme, rennin and pepsin
  • Provides suitable acidic medium for action of gastric enzymes and kills of potentially harmful microorganisms
• Ingestion

  • In stomach - (Pepsin and rennin)
  • Pepsin and rennin both act on proteins
  • Pepsin digests proteins to polypeptides
  • Rennin curdles milk by converting soluble caseinogen to insoluble casein
  • This is because milk passes through duodenum as easily as water so not enough time for pepsin to act on milk
  • Insoluble casein stays long enough in stomach for pepsin to act on it