white blood cell casts

Overview of the Mechanisms of Kidney Function
Ms. Cornwall is admitted with pyelonephritis. She has chills, and her temperature is 101?F. She is complaining of flank pain, frequency, and dysuria. Her urine has white blood cell casts and shows growth of Escherichia coli (E. coli).
Based on the above scenario, answer the following questions:
Why does she have bacteria and white blood cell casts in her urine? Include the pathophysiological response of body for your analysis.
What are the differences when comparing prerenal acute renal injury, intrarenal acute renal injury, and postrenal acute renal injury? Give examples of each and pathological processes related to each disease process.