function of the kidney 1

• whats filtered


  • water
  • amino acids
  • glucose
  • urea
  • inorganic mineral ions
• ultrafiltration


  • filtering blood at the molecular level
  • blood flows into glomerulus through afferent arteriole (wider than efferent arteriole) and carries blood away from glomerulus
  • difference in diameters ensures that blood in capillaries of the glomerulus maintains a higher pressure than pressure in Bowman's capsule
• what is left in the capillary


  blood cells and proteins. presence of proteins shows blood has a very low water potential - helps reabsorb water at a later stage
• function of nephrons

  • as fluid from Bowman's capsule passes along nephron tubule, it's composition is altered by selective reabsorption
• function of nephrons


  • in proximal convoluted tubule the fluid is altered by reabsorption of all sugars, most mineral ions and some water
  • 85% of fluid reabsorbed here
  • cells of these tubules have a highly folded surface producing a brush boarder which increases surface area
• function of nephrons 


  • in descending limb of loop of Henle, water potential of fluid is decreased by addition of mineral ions and removal of water
  • in ascending limb of loop of Henle, water potential is increased as mineral ions are removed by active transport
• function of nephrons

  • in the collecting duct, water potential is decreased again by removal of water. Final product in the collecting duct is urine.
  • tis product ensures the final product (urine) has a low water potential. urine therefore has a higher concentration of solutes than is found in blood and tissue fluid.
  • urine passes into pelvis and down the ureter to the bladder
• selective reabsorption 


  • involves active transport and cotransport
  • cell surface membrane in contact with tubule fluid is highly folded to form microvilli. Microvilli increase surface area for reabsorption.
  • cell surface membrane also contains special cotransporter proteins that transport glucose or amino acids, from tubule into the cell.
• selective reabsorption


  • opposite membrane of the cell, close to tissue fluid and blood capillaries, is also folded to increase its surface area. This membrane contains sodium/potassium pumps that pump sodium ions out of cell and potassium ions into cell
  • cell cytoplasm has many mitochondria. indicates that an active, or energy-requiring process is involved, many mitochondria will produce a lot of ATP
• mechanism of reabsorption


  • movement of sodium ions and glucose into the cell is driven by concentration gradient created by pumping sodium ions out of the cell.
  • sodium ions move into cell by facilitated diffusion but they cotransport glucose or amino acids against their concentration gradient. called secondary active transport
  • movement of these substances reduces water potential of the cell so water is drawn in from tubule by osmosis. As substances move through to blood, water follows