GCSE Biology 3

Filtration units in the kidney

• Ultrafiltration 
• reabsorption 
• release of waste

• A highs pressure is built up which squeezes water , urea , ions and sugar out of the blood and into the bowman's capsule 
• the membranes between the blood vessels and the bowman's capsule act like filters so big molecules like protein ands and red blood cells are not squeezed out . They stay in the blood

• As the liquid flows along the nephron , useful substances are reabsorbed back into the blood : 
• 1) all the sugar is reabsorbed this involves the process of active transport against the concentration gradient
• 2) sufficient ions are reabsorbed . Excess ions are not . Active transport is needed 
• 3) sufficient water is reabsorbed

The remaining substances including urea continue out the he nephron , into the ureter and down the bladder as urine

• waste substances from the blood
• 1) if the kidneys didn't work properly , waste substances build up In the blood and you lose your ability to control the levels of ions and water in your body . eventually this leads to death 
• 2) people with kidney failure can be kept alive by having dialysis treatment - where the machines do the job of the kidneys . Or they have a kidney transplant

Filter the blood

• 
• dialysis has to be done regularly to keep the concentrations of dissolved substances in the blood at normal levels , and toremove waste   substances  
• in a dialysis machine the persons blood flows alongside a selectively permeable barrier , surrounded bY dialysis fluid . Its permeable to things like ions and waste substances , but not big molecules like protein (just like membranes in the kidney) 
• the dialysis fluid has the same concentration of dissolved ions and glucose as healthy blood 
• this means that useful dissolved ions and glucose Wont be lost from the blood during dialysis
• only waste substances such as urea and excess ions and water diffuse across the Barrier