Drs. Foster and Smith have a lot of good pet health info (searchable and understandable) on PetEducation.com. I don't know if it is completely new or not, but they are currently advertising a write-up on the urinary system - kidneys, bladder, etc. Have a look!
Urinary System in Mammals: Anatomy and Function
There is a new article on coughing. It helps to explain why it is so hard to figure out why a dog is coughing.
Coughing in Dogs and Cats: Causes, Diagnosis, and Treatment