chapter 14 science

• human digestive system - chemically break down large, insoluble, complex molecules into small, soluble, simple molecules to be absorbed into the blood
• nutrients

  1. provide us with chemical energy that is released from nutrients via respiration

  _converted to heat energy to maintain our body temperature

  _do work

  _energy needed to maintain bodily functions eg. breathing, pumping of heart

  
  

  2. provide us with raw materials to

  _make new cells and tissues for growth and repair worn-out tissues

  
  

  3. keep us healthy
• carbohydrate

  eg. rice, bread, potato, biscuits

  • starch -> maltose -> glucose
  • immediate source of energy
  • indigestible carbohydrates make up part of the fibre in our bodies
  • fibre passed out, forms bulk of our faeces
  • digestion of carbs start at mouth
• protein

  eg. beans, peas, milk, fish

  • protein -> polypeptide -> amino acid
  • make new cells for growth, repair worn-out tissue
  • make complex proteins called enzymes
  • provides energy ONLY when insufficient carbs and fats
• fats

  eg. tuna, peanuts, avocado, butter

  • fat -> glycerol + fatty acids
  • provide energy
  • stored in body to keep us warm
  • digestion starts at small intestine
• large and complex molecules (eg. maltose, polypeptides, fats) cannot pass through cell surface membrane of small intestine cells -> need for digestion

  
  

  partially permeable - only allow some substances (small particles) to pass through but not others (large particles)

  
  

  digestion -> pass through cell surface membrane -> absorbed into blood -> blood transports nutrients to tissue cells for cellular processes
• 1. Physical digestion

  : breaking down of food into smaller pieces

  • physical/mechanical means (grinding, crushing, mixing)
  • no chemical changes to molecules of food

  2. Chemical digestion

  : process of breaking down large, insoluble, complex food molecules into small, soluble, simpler molecules

  • enzymes needed to help in digestion
• enzymes -> biological molecules made by digestive system that speed up digestion

  • act on food molecules = digestive enzymes
  • specific in action = only act on one type of substrate
  • complementary = unique shape, only fit specific substrate

  carbohydrase -> carbohydrates

  protease -> proteins

  lipase -> fats

  after digestion, enzymes remain chemically unchanged, can be reused -> only small amount needed
• mouth

  • jaw muscles and teeth cut and grind food into smaller pieces through chewing
  • secretes saliva

  - softens, lubricates food for swallowing

  - contains carbohydrase (starch -> maltose)
• oesophagus

  • 25cm long, move food to stomach by peristalsis
  • peristalsis: muscles of digestive system contract and relax to produce wave-like movement that pushes food along the gut
  • carbohydrase (from mouth) continues to digest starch as food moves down the oesophagus
• stomach

  • food stays for 3-4 hours
  • secretes gastric juices

  - hydrochloric acid -> kills harmful microorganisms in food, provides suitable condition for stomach protease to act in

  - protease -> proteins to polypeptides

  • thick layer of mucus to protect tissues from damage by hydrochloric acid and protease
  • churning: stomach muscles contract and relax to break food down into smaller pieces and mixes food well with gastric juice
  • muscles at both end of stomach - control amount of food entering/leaving stomach
• small intestine

  _completely digest all complex nutrients

  • fats -> glycerol + fatty acids
  • remaining starch -> maltose
  • maltose (from mouth) -> glucose
  • remaining protein -> polypeptides
  • polypeptides (from stomach) -> amino acids

  _most water and mineral salts absorbed in small intestine (NOT LARGE INTESTINE!)
• large intestine

  • colon: SOME of remaining water and mineral salts absorbed from undigested food
  • rectum: undigested food forms faeces, temporarily stored here before leaving through anus
• • digested nutrients transported by blood to all parts of body to be used by tissue cells

  glucose -> broken down during cellular respiration to release energy - used for other cellular processes

  
  

  amino acids -> used as raw materials to make new cells, repair worn-out cells - energy required

  
  

  fatty acids and glycerol -> make fats - used to make cell surface membranes/ stored under skin (reduce heat loss)
• diabetes -> blood sugar level too high after meals

  
  

  1)body produces insufficient insulin

  OR

  2)body produces sufficient insulin but tissue cells do not respond to insulin

  
  

  symptoms

  1. slow healing of wounds
  2. constant hunger
  3. frequent urination
  4. tingling or numbness in hands and feet
  5. blurred vision
• diabetes

  • linked to other health conditions

  eg. obesity, heart attacks, kidney problems, high blood pressure, blindness, stroke

  • caused by excess intake of carbohydrates over an extended period of time
  • detect BSL with conventional blood sugar meter
  • BSL monitoring device can be linked to phone
• reduce risk of diabetes

  1. regular health screenings
  2. healthy, balanced diet : more whole grains, fruits, vegetables, lean meat -> avoid food high in salt, sugar, saturated fats
  3. exercise regularly (5 days a week, 30 min each)
  4. avoid smoking, drinking alcohol
• constipation

  • caused by faeces moving too slowly through large intestine
  • too much water to be absorbed from faeces
  • faeces becomes hard and dry -> difficult to pass out

  caused by

  1. stress
  2. certain medication
  3. insufficient fibre in diet
  4. insufficient water consumed

  • eat more food high in fibre, drink more water, adequate exercise
• gastric pain

  • caused by gastritis -> painful swelling and inflammation of stomach lining

  symptoms - upper abdominal pain, nausea, bloating

  • caused by bacterial/viral infection, skipping meals, consuming alcohol, caffeine, too much oily food
• food poisoning

  • caused by eating food contained with bacteria that can lead to diarrhoea, life-threatening diseases (eg. cholera, salmonella infection)
• 1. Handling food safety

  • use separate utensils and crockery for raw/cooked food
  • cover food properly before placing in refrigerator
  • store cooked food above raw food in fridge (so juices cannot drip and contaminate)
  • keep raw food below 5°C

  2. Choose food carefully

  • bottled milk and drinks must be tightly sealed
  • do not consume food from dented/ bloated cans
  • select food with expiry dates that have not passed
  • chilled food stored between 0°C and 4°C. frozen food below -18°C
• benefits of bacteria

  • help fight off some diseases, absorb nutrients, minerals salts, produce enzymes, vitamins, amino acids
  • help digest carbohydrates
  • make food - coffee, chocolate, yoghurt, cheese, vinegar, pickles