7. Human nutrition

• Balanced diet: provides all dietary requirements in the correct proportions (carbohydrates, proteins, fats, vitamins, minerals)
• Lack of protein: lose muscle mass, slow metabolism...
• Lack of lipids: weak immune system, poor growth, poor vision, poor taste, poor smell
• Lack of carbohydrates: blood sugar level may drop (hypoglycemia)
• Source of important dietary:

  • carbohydrates: bread, pasta...
  • fats: butter, cream...
  • proteins: fish, beef, chicken...
  • vitamins: citrus fruit (vitamin C), egg yolk (vitamin D)
  • mineral salt: milk (calcium), spinach (iron)
  • fibre: beans, peas
  • water
• Ingestion: the taking of substances into the body through the mouth
• Mechanical digestion: the breakdown of food into smaller pieces without chemical change to the food molecules
• Chemical digestion: the breakdown of large, insoluble molecules into small, soluble molecules
• Absorption: the movement of small food molecules and ions through the wall of the intestine into the blood
• Assimilation: the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells
• Egestion: the passing out of food that has not been digested or absorbed, as faeces, through the anus
• Diarrhea: the loss of water faeces
• Treatment for diarrhea (oral rehydration therapy):

  • drinks with small amount of salt and sugar to rehydrate the person
• Cholera:

  • a bacteria that produce a toxin that would release chloride ions into the small intestine
  • lowers water potential from within -> causes water from outside to move in due to osmosis
  • dehydration and diarrhea occurs
• Alimentary canal diagram:

  A) mouth

  B) oesophagus

  C) liver

  D) stomach

  E) gall bladder

  F) duodenum

  G) pancreas

  H) ileum

  I) colon

  J) appendix

  K) rectum

  L) anus

  
• Main organs in alimentary canal (P1):

  • mouth: Contains teeth for mechanical digestion, food is mixed with amylase - ingestion take place here
  • salivary glands: produce saliva contain amylase and help food slide down the oesophagus
  • oesophagus: tube shape organ to transport food from mouth to stomach
  • stomach: has pepsin to breakdown protein into amino acids & kill bacteria with hydrochloric acid
• Main organs in alimentary canal (P2):

  • duodenum (small intestine): fats emulsified by bile and digested by pancreatic lipase to form fatty acids and glycerol; trypsin break down starch
  • ileum (small intestine): maltase breakdown maltose to glucose, where absorption take place, having villi & microvilli
  • pancreas: produce amylase, trypsin and lipase
  • liver: produce bile, deamination, makes urea to be sent to kidney
• Main organs in alimentary canal (P3):

  • gall bladder: stores bile from the liver
  • colon (large intestine): absorption of minerals and vitamins & reabsorbing water from waste
  • rectum (large intestine): where faeces are temporarily stored
  • anus: a ring of muscle that controls when faeces is released
• Chemical digestion:

  • producing small, soluble molecules that can be absorbed in the alimentary canal

  Enzymes:

  • amylase (mouth): break down starch -> simpler sugars
  • protease (pancreas): break down protein -> amino acids
  • lipase (pancreas, mouth, stomach): break down fats -> fatty acids and glycerol
• Hydrochloric acid in gastric juice:

  • denaturing enzymes in harmful microorganism
  • giving the optimum pH for pepsin activity
  • kill pathogens
• Digestion of starch in alimentary canal:

  • amylase secreted into alimentary canal and break down starch to glucose on membrane of he epithelium lining of small intestine
• Bile:

  • an alkaline mixture that neutralises the acid mixture of food & gastric juices
  • provide a suitable pH for enzyme action in the duodenum from the stomach
  • emulsifying fats - increase surface area for the chemical digestion of fat to fatty acid & glycerol by lipase
• Absorption and villus:

  • small intestine: region for the absorption of digested food
  • water is absorbed in both the small intestine & colon (mostly in s.intestine)
  • villi: increasing surface area for absorption, have tiny folds on cell outside called microvilli
  • capillaries: provide good blood supply & a steep concentration gradient
  • lacteals: absorbs fatty acid and glycerol