Urinary System

The urinary system consists of the kidneys, ureters, bladder, and urethra. The most striking difference between the urinary system of marine mammals and that of most terrestrial animals is that marine mammals have reniculated kidneys.

Reniculated kidneys are an adaptation for concentrating urine when fresh water is scarce and appear as a “sack of grapes”. Each grape is an individual small kidney which can be seen when the kidney is bisected.

Detailed annotated images of the urinary system in a California Sea Lion are shown below.  CLICK on an image to see an enlarged view.