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The Renal System

Biology (Year 12) - Osmoregulation

Ben Whitten

What are the kidneys? The kidneys are two bean-shaped organs, each about the size of a fist. They are located just below the rib cage, one on each side of your spine. The kidneys predominantly play a key role in osmoregulation, their osmoregulatory functions including;

  • Removal of nitrogenous wastes

  • Regulation of blood water concentration

  • Regulation and maintenance of blood ion levels

How are the kidneys' structure related to their function? How does filtration work? The cortex and medulla make up two of the main layers in a kidney and are composed of individual filtering units known as nephrons (the functional units of the kidneys), which act to filter the blood in order to both regulate the concentrations of chemicals and to produce urine as a waste product. At the end of each nephron, in the cortex of the kidney are cup-shaped structures termed Bowman's capsules; each one surrounds a group of capillaries called a glomerulus. Blood travels from the renal arteries into the glomerulus of each nephron; at the glomerulus, plasma is forced out through the walls of the glomerulus, then in through the outer layers of the Bowman's capsule to its interior, being filtered in the process. After entering the capsule, the filtrate flows along the proximal convoluted tubule to the loop of Henle, and then to the distal convoluted tubule and the collecting ducts, finally flowing into the ureter. Each of the various components of the nephrons are selectively permeable to different molecules, and enable the complex regulation of water and ion concentrations in the body.


  • Renal arteries carry blood to the kidney

  • Renal veins carry blood away from the kidney

  • The glomerulus is the site in the nephron where fluid and solutes are filtered out to form a glomerular filtrate (process called filtration)

  • The proximal and distal convoluted tubules, the loop of Henle and the collecting ducts are sites for reabsorption of water and ions (where reabsorption is the process of water, ions and other substances in the filtrate being absorbed back into the blood)

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