Biology - B3.3 - Keeping Internal Conditions Constant

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B3.3.1 - Controlling Internal Conditions

  • Homeostatis: keeping conditions within a narrow range - must control temperature, blood, glucose, water and ion content, waste product levels
  • Waste products that have to be removed: CO2 - removed via lungs when we breathe out, urea - produced in liver fom amino acid breakdown, removed by kidneys in urine, temporarily stored in bladder
  • Water and ions enter body when we eat/drink - if content is wrong, too much water may move in or out of cells - could damage or destroy cells
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B3.3.2 - The Human Kidney

  • Body has two kidneys - filter blood - excrete uneeded substances and keep needed ones
  • Healthy kidney produces urine by: filtering blood -> reabsorbing all the sugar -> reabsorbing dissolved ions needed by body -> reabsorbing as much water as needed -> releasing urea, excess ions and water in urine
  • Urine temporarily stored in bladder before removed from body
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B3.3.3 - Dialysis - an Artificial Kidney

  • Person kept alive by dialysis if kidney fails
  • Dialysis machine works same as kidney - blood flows between partially permeable membrane
  • Dialysis fluid contains same concentration of useful substances as blood, eg. glucose and mineral ions: useful substances don't diffuse out of body: don't need to be reabsorbed - urea diffuses out of blood into dialysis fluid
  • Dialysis restores concentration of substances in blood back to normal - but has to be done regularly
  • Kidney becomes avaliable: patient may have kidney transplant - successful transplant = no more dialysis
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B3.3.4 - Kidney Transplants

  • Kidney transplant is often better than dialysis - diseased kidney replaced with healthy one - may be obtained from dead person or living donor
  • New kidney must be good tissue match: rejected otherwise
  • Proteins (antigens) on surface of cells - recipients antigens may attack donor organs antigens: recognise them as being foreign
  • Recipient must take drugs after transplant to suppress immune response to prevent rejection - immunosuppressants
  • Risk from transplant operation, treatment involves suppressing immune system - vunerable to common infections
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B3.3.5 - Controlling Body Temperature

  • Temperature ~37C for enzymes - core body temperature has to be stable
  • Body temperature monitered and controlled by thermoregulatory centre in brain - has receptors to detect blood temperature - receptors in skin send impulses to brain about skin temperature
  • Skin looks red when hot: increased blood flow
  • Sweating cools body - water lost from skin: water taken in to balance it
  • Core temperature rises - blood vessels near surfaces dilate to flow more through capillaries: energy transferred by radiation: skin cools - more sweat produced, water evaporates from skin surface, energy needed for water evaporation comes from surface: cool down
  • Core temperature falls - blood vessels near surface: less blood flows through skin capillaries: less energy radiated - muscles contract quickly (shiver): respiation needed: energy released warms blood
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B3.3.6 - Treatment and Temperature Issues

  • When chosing treatment need to consider: general health, length of time on dialysis, cost of treatment, risk of operation, avaliability of donors
  • Ethical issues: should transplant regisiter be opt out? should donors be paid? should people pay to jump queue for transplant?
  • Enzymes don't work properly in extreme temperatures
  • Small children have large surface area-volume ratio - transfer energy to surroundings quickly in cold conditions and dyhydrate quickly in hot conditions
  • Body temperature too low: enzymes work too slowly: little energy released - if child dehydrates, can't cool down: overheat: denature enzymes
  • Old people suffer from hypothermia when cold - don't move much to release energy from respiration in muscles
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B3.3.7 - Controlling Blood Glucose

  • Pancreas monitors and controls glucose levels in blood - too much glucose: pancreas produces insulin
  • Insulin moves glucose from blood to cells - excess glucose in liver stored as glycogen
  • No or little insulin produced by pancreas: high blood sugar levels - type 1 diabetes - controlled by insulin injections and careful attention to diet and exercise
  • Insulin causes blood glucose levels to fall - if receptors in pancreas detect levels are too low, pancreas releases glucagon (hormone) that causes gycogen to change into glucose, which is released back into blood
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B3.3.8 - Treating Diabetes

  • Type 1 diabetes traditionall treated with human insulin produced by genetically engineered bacteria - has to inject it every day
  • Active diabetics have to match amount of insulin injected with diet and exercise - some use pumps attached to body and can adjust levels injected by pumps
  • Developing new ways of treating or curing diabetes: psncreas transplants, transplanting pancreas cells, use embryonic stem cells to produce insulin secreting cells, use adult stem cells from diabetic patients, genetically engineer pancreas cells to make them work properly
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