Question for Anatomy & Physiology (Need in a few MINUTES!!!)

I responded to a discussion question for my A&P class about bladdar and renal system.

The instructor responded the following:

"Well done. You are correct that the urinary bladder and the renal systems are incredibly important in maintaining homeostasis. Many of us have experienced a urinary tract infections that was extremely uncomfortable but which did not 'alert' the immune system to launch the inflammatory response.

Isn't it interesting that urine is sterile when first produced? How then it is at risk for contamination? Your thoughts?"

Can you help me respond the highlighted part???

I NEED IT IN A FEW MINS!!!!

No Plagarism. Please cite and reference

Thank you!