Key   functions   of  excretory
   systems include:
<P>
<BR><LI> Filtration.
Water  and  solutes are forced across the membranes of capillaries
to produce a filtrate.
<BR><LI> Reabsorption.
Valuable  solutes  such  as  glucose and amino acids are reclaimed
from the filtrate by active transport.
<BR><LI> Secretion.
Toxins  and  excess  ions  are  extracted  from body fluids to the
filtrate by active transport.
<BR><LI> Excretion.
The filtrate leaves the system.