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The Excretory System

  • The excretory system is responsible for the removal of nitrogenous wastes and for osmoregulation.
  • The functional unit of the kidney is the nephron. Filtration takes place in the glomerulus where pressure drives water small molecules across the glomerular membrane
  • Reabsorption of water and substances such as NaCl, amino acids and glucose takes place in in the proximal convoluted tubule. Other substances are secreted into the PCT.
  • Aquaporins in the descending loop of Henle allow for water reabsorption in this segment of the tubule.
  • The ascending loop of Henle is impermeable to water. The ascending loop of Henle maintains the concentration gradient from cortex to medulla by transporting NaCl into the interstitium.
  • In the distal convoluted tubule both reabsorption and secretion take place.
  • The collecting duct is permeable to water when acted upon by antidiuretic hormone (ADH). ADH stimulates the reabsorption of water by the kidney.
  • Aldosterone is released in response to low blood pressure or blood volume and stimulates the reabsorption of Na+ by the distal convoluted tubule.

The Excretory System

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AP Biology Intro