The urinary system or tract includes the kidneys, the ureters (tubes that connect the kidneys to the bladder), the bladder, and the urethra (the tube through which urine exits the body). The urinary system has several important functions. It gets rid of the waste products that are created when food is transformed into energy. It also maintains the correct balance of water and electrolytes (salts) within the body's cells. Another key function is the production of hormones called erythropoietin and renin, which are important in maintaining healthy blood pressure, producing blood cells, and absorbing salt correctly. Finally, the urinary system processes vitamin D.  

Acute kidney failure is an abrupt decline in function that occurs over a period of days. Dogs can develop acute kidney problems as a result of ingesting toxins, including antifreeze, certain medications, tainted foods, etc. Other reasons for this type of kidney failure include decreased blood flow or oxygen delivery to the kidneys, infections and urinary obstruction.

Chronic: While some kidney problems have an immediate cause that can be treated, chronic kidney disease shows up over a period of time and its causes are harder to determine. This condition develops slowly and affects mostly older dogs. It is often caused by underlying illness and congenital and hereditary conditions.