kidney structure

• fine structure of the kidney

  • bulk of each kidney consists of tiny tubules called nephrons.
  • each kidney contains about one million nephrons
  • each nephron starts in the cortex at a cup shaped structure called the bowman's capsule
  • remainder of nephron is a coiled tubule that passes through the cortex, forms a loop down into medulla and back to the cortex before joining a collecting duct that passes back down into the medulla
• endothelium of the capillary


  Narrow gaps between cells of the endothelium of the capillary wall. cells of the endothelium also contain pores, called fenestrations. gaps allow blood plasma and the substances dissolved in it to pass out of the capillary
• basement membrane


  membrane consists of fine mesh of collagen fibres and glycoproteins. this mesh acts as a filter to prevent passage of molecules with relative molecular mass greater than 69000. means most proteins held in capillaries in the glomerulus
• epithelial cells of the Bowman's capsule


  cells called podocytes have a specialised shape. have many finger like projections called major processes. on each major process are minor processes or foot processes that hold cells away from endothelium of the capillary. these projections ensure there are gaps between the cells. fluid from blood in glomerulus can pass between these cells into lumen of bowman's capsule.
• bowman's capsule leads into the rest of the tubule, which has 3 parts

  • proximal convoluted tubule
  • loop of henle
  • distal convoluted tubule
• fluid from many nephrons enters the collecting ducts, which pass down through the medulla to the pelvis at the centre of the kidney.
• blood supply and filtering

  renal artery splits to form many afferent arterioles, which lead to a knot of capillaries called the glomerulus. blood from the glomerulus continues into efferent arteriole which carries blood to more capillaries surrounding rest of tubule. these capillaries eventually flow together into renal vein. each capillary surrounded by Bowman's capsule. fluid from blood pushed into bowman's capsule by ultrafiltration.
• afferent arteriole thicker than efferent arteriole.