GCSE AQA Biology 3 Kidneys & Homeostasis

1. Definition: Maintenance of a constant internal environment
2. 6 things to be controlled:
   1. Body temp.

      Nota:

      • Can get too hot or cold
   2. Water content

      Nota:

      • Can't get too high or low - too much water could move into/out of cells - damaging them
   3. Ion content

      Nota:

      • Can't get too high or low - too much water could move into/out of cells - damaging them
   4. Blood sugar level

      Nota:

      • Needs to stay within certain limits
   5. Carbon dioxide

      Nota:

      • Product of respiration - must be removed in lungs when breathing out
   6. Urea

      Nota:

      • Waste product made from excess amino acids

1. Enzymes in human body work best at 37 degrees C
   1. If too hot/cold - won't work properly

      Nota:

      • In extreme cases - could lead to death
2. Thermoregulatory centre in brain - contains receptors that are sensitive to temp. of blood in brain
   1. Also receives impulses from skin about skin temp.
3. When you're too hot...
   1. Hairs lie flat
   2. Sweat is produced by sweat glands - evaporates, removing heat
   3. Blood vessels supplying skin dilate - more blood flow to surface of skin (makes it easier for heat to be transferred from blood to environment)
4. When you're too cold...
   1. Hairs stand up - trap insulating layer of air
   2. No sweat produced
   3. Blood vessels near skin constrict - close off blood supply
   4. Shiver (muscles contract automatically) - requires respiration which releases energy to warm body

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

Nota:

• Usually contain water, sugar & ions

1. Can help body replace water & ions lost in sweat & sugar used up by muscles during exercise

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

1. If kidneys don't work properly - waste substances build up & you can't control ion and water level
2. People with kidney failure can be kept alive by having dialysis treatment or kidney transplant
3. Dialysis treatment
   1. Must be done regularly

      Nota:

      • To keep concentrations of dissolved substances at normal levels and remove waste substances
   2. In dialysis machine, person's blood flows alongside selectively permeable barrier, surrounded by dialysis fluid

      Nota:

      • Permeable to ions, waste substances but not big molecules like proteins
      1. Fluid has same concentration of ions & glucose as healthy bood
         1. Only waste substances (urea) & excess ions & water diffuse across
   3. Cons: Have to have session 3 times a week (3-4hrs each), may cause blood clots/infection
4. Kidney transplants
   1. Healthy kidneys transplanted from people who have died suddenly (& are on the register)/are still alive (we have 2)
   2. Donor kidney can be rejected by immune system (foreign antigens attacked by antibodies) so precautions are taken:
      1. Donor with similar tissue type is chosen

         Nota:

         • Tissue type bases on antigens (proteins on surface of cells) Have to wait a long time
      2. Patient given immunosuppressants

         Nota:

         • Stop immune system attacking kidney

1. Insulin & glucagon control blood glucose level
   1. Eating foods containg carbs puts glucose into blood from gut
   2. Normal metabolism of cells removes glucose
      1. Exercise removes much more
   3. Changes in blood glucose are monitored/controlled by pancreas, using insulin & glucagon...
      1. When blood glucose level is too high:
         1. 1) Insulin secreted by pancreas
            1. 2) Tells liver to turn glucose into glycogen
               1. 3) Blood glucose reduced
      2. When blood glucose level is too low:
         1. 1) Glucagon secreted by pancreas
            1. 2) Tells liver to turn glycogen into glucose
               1. 3) Blood glucose increased
2. Type 1 Diabetes

   Nota:

   • Condition where pancreas produces little/no insulin - person's blood glucose can rise to a level that can kill them
   1. Can be controlled by: Avoiding foods rich in sugars, doing exercise & injecting insulin
      1. Amount of insulin needed depends on person's diet & activity
         1. Insulin used to be extracted from pig/cow pancreases
            1. But is now made by genetic engineering - human insulin doesn't cause adverse reaction
               1. Injecting can control level but not as well as normal pancreas - diabetics can have a pancreas transplant
                  1. Has same issues as kidney transplant but could mean no more injecting