Formation of urine

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  • Created by: Steff06
  • Created on: 28-02-16 12:07
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  • Formation of urine
    • Ultrafiltration:
      • Blood flows into the GLOMERULUS from the AFFERENT arteriole. The AFFERENT arteriole is WIDER than the EFFERENT arteriole.
      • Difference in diameters of arterioles ensures that blood in the capillaries of the glomerulus is under increased PRESSURE.
      • Pressure in the glomerulus is higher than in the Bowman's capsule.
    • Glomerular filtration:
      • 1. Glomerulus brings a large surface area of blood capillaries in close contact with the Bowman's capsule.
      • 2. Liquid and small molecules are filtered from the blood under pressure.
      • 3. Glomerular filtrate is produced containing WATER, GLUCOSE, SALTS, UREA, AMINO ACIDS.
      • 4. PROTEINS and BLOOD CELLS are TOO BIG to pass into the tubule.
    • ADAPTIONS of Bowman's capsule for ultrafiltration:
      • 1. ENDOTHELIUM of the capillary. Has NARROW GAPS between cells and is ONE CELL thick.
        • Provides SHORTER DIFFUSION distance. Gaps allow blood plasma and substances dissolved in it to PASS THROUGH.
        • Acts as FILTER to prevent passage of molecules greater than 69000.
      • 3. PODOCYTES (Epithelial cells of Bowman's capsule). Have specialised finger-like PROJECTIONS (major processes).
        • These ensure there are GAPS between the cells so fluid from blood can pass into LUMEN of Bowman's capsule.
    • Presence of PROTEINS left in the capillary means the blood has a very LOW WATER POTENTIAL.
      • This ensures some fluid is retained in the blood and is important to help to REABSORB WATER later on.


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