Human excretory system.
<P>
<lI> A pair of kidneys serve as the principal site of water balance and
salt regulation.
<lI> Each  kidney  is  composed  of  an outer renal cortex and an inner
renal medulla.
<lI> Each kidney is made of several functional units called nephrons.
<lI> The nephrons produce urine, which is drained by the ureter.
<P>
   <A ClAsS=ACT Href="http://media.pearsoncmg.com/bc/bc_campbell_biology_7/media/activities/load.html?44&amp;A" oNClick="popact('http://media.pearsoncmg.com/bc/bc_campbell_biology_7/media/activities/load.html?44&amp;A');txtcolor('excretory_system6','gray');return false;" Id=excretory_system6 ClAsS=ACT>Review:</A> Structure of the Human Excretory System