GCSE AQA Biology 3 Kidneys & Homeostasis

GCSE AQA Biology 3 Kidneys & Homeostasis

1. Homeostasis

   • Definition: Maintenance of a constant internal environment
   • 6 things to be controlled:
     • Body temp.
       • Can get too hot or cold
     • Water content
       • Can't get too high or low - too much water could move into/out of cells - damaging them
     • Ion content
       • Can't get too high or low - too much water could move into/out of cells - damaging them
     • Blood sugar level
       • Needs to stay within certain limits
     • Carbon dioxide
       • Product of respiration - must be removed in lungs when breathing out
     • Urea
       • Waste product made from excess amino acids

2. Controlling body temp.

   • Enzymes in human body work best at 37 degrees C
     • If too hot/cold - won't work properly
       • In extreme cases - could lead to death
   • Thermoregulatory centre in brain - contains receptors that are sensitive to temp. of blood in brain
     • Also receives impulses from skin about skin temp.
   • When you're too hot...
     • Hairs lie flat
     • Sweat is produced by sweat glands - evaporates, removing heat
     • Blood vessels supplying skin dilate - more blood flow to surface of skin (makes it easier for heat to be transferred from blood to environment)
   • When you're too cold...
     • Hairs stand up - trap insulating layer of air
     • No sweat produced
     • Blood vessels near skin constrict - close off blood supply
     • Shiver (muscles contract automatically) - requires respiration which releases energy to warm body

3. Kidney involvement in homeostasis

   • Act as filters to clean blood
     • Main roles...
       • Removal of urea
         • Proteins can't be stored so excess amino acids are converted into carbs and fats
           • Process occurs in liver - urea produced as waste product
             • Urea is poisonous - released into bloodstream by liver, kidneys filter it out. temporarily stored in bladder before excretion
       • Adjustment of ion content
         • Ions (e.g. Na) are taken into body in food & absorbed into blood
         • If ion (or water) content is wrong - could upset balance between them
         • Excess ions removed by kidneys
           • Some are also lost in sweat
       • Adjustment of water content
         • Water taken into body as food/drink & lost in...
           • Urine
           • Sweat
           • Air we breathe out
         • Water balance is between...
           • Liquids consumed
           • Amount sweated out
           • Amount excreted by kidneys in urine

4. Sports drinks

   • Usually contain water, sugar & ions
   • Can help body replace water & ions lost in sweat & sugar used up by muscles during exercise

5. Kidney function

   • Nephrons are filtration units in kidney
     • 1) Ultrafiltration
       • High pressure built up - squeezes water, urea, ions & sugar out of blood, into Bowman's capsule
         • Membranes act like filters - big molecules like proteins & blood cells stay in blood
       • 2) Reabsorption
         • As liquid flows along nephron - useful substances reabsorbed:
           • All the sugar (involves active transport), sufficient ions (active transport involved) & sufficient water
         • 3) Release of wastes
           • Remaining substances (including urea) continue out of nephron, into ureter & down to bladder as urine

6. Kidney failure

   • If kidneys don't work properly - waste substances build up & you can't control ion and water level
   • People with kidney failure can be kept alive by having dialysis treatment or kidney transplant
   • Dialysis treatment
     • Must be done regularly
       • To keep concentrations of dissolved substances at normal levels and remove waste substances
     • In dialysis machine, person's blood flows alongside selectively permeable barrier, surrounded by dialysis fluid
       • Permeable to ions, waste substances but not big molecules like proteins
       • Fluid has same concentration of ions & glucose as healthy bood
         • Only waste substances (urea) & excess ions & water diffuse across
     • Cons: Have to have session 3 times a week (3-4hrs each), may cause blood clots/infection
   • Kidney transplants
     • Healthy kidneys transplanted from people who have died suddenly (& are on the register)/are still alive (we have 2)
     • Donor kidney can be rejected by immune system (foreign antigens attacked by antibodies) so precautions are taken:
       • Donor with similar tissue type is chosen
         • Tissue type bases on antigens (proteins on surface of cells) Have to wait a long time
       • Patient given immunosuppressants
         • Stop immune system attacking kidney

7. Controlling blood glucose

   • Insulin & glucagon control blood glucose level
     • Eating foods containg carbs puts glucose into blood from gut
     • Normal metabolism of cells removes glucose
       • Exercise removes much more
     • Changes in blood glucose are monitored/controlled by pancreas, using insulin & glucagon...
       • When blood glucose level is too high:
         • 1) Insulin secreted by pancreas
           • 2) Tells liver to turn glucose into glycogen
             • 3) Blood glucose reduced
       • When blood glucose level is too low:
         • 1) Glucagon secreted by pancreas
           • 2) Tells liver to turn glycogen into glucose
             • 3) Blood glucose increased
   • Type 1 Diabetes
     • Condition where pancreas produces little/no insulin - person's blood glucose can rise to a level that can kill them
     • Can be controlled by: Avoiding foods rich in sugars, doing exercise & injecting insulin
       • Amount of insulin needed depends on person's diet & activity
         • Insulin used to be extracted from pig/cow pancreases
           • But is now made by genetic engineering - human insulin doesn't cause adverse reaction
             • Injecting can control level but not as well as normal pancreas - diabetics can have a pancreas transplant
               • Has same issues as kidney transplant but could mean no more injecting