|MadSci Network: Zoology|
Since the polar bear is a mammal it will have essentially all the same major organs and structures that other mammals have internally. This would include things like a four-chambered heart, paired lungs attached to trachea and bronchii, a complete gastrointestinal (GI) tract, a pair of kidneys attached to a urinary bladder by ureters with a urethra leaving the bladder, a central and peripheral nervous system, and a full set of endocrine glands to name much of the most important stuff. I looked on the web also and could find nothing on the internal anatomy of Ursus meritimus (Polar bear) in a short scan through some search engines. One spot that gave some interesting information was: http://tqjunior.thinkquest.org/3500/polarbear.htm, and you might check that one out.
If you go to the library and get an advanced anatomy book for humans and look for a cross section it will be very similar to what the bear would look like. I must say that cross-sectional anatomy is always the most advanced form of studying a system and so there may not be anything available for polar bears. You might try a veterinarian (DVM) or better yet, if you have a veterinary school near where you live they might have something in print that would be helpful.
Best wishes for hunting further,
Try the links in the MadSci Library for more information on Zoology.