Final answer:
The movement of microbes out of the urinary tract is primarily achieved through filtration in the kidneys, with the subsequent urine flow helping to excrete them.
Step-by-step explanation:
The mechanism that moves microbes out of the urinary tract as part of the first line of defense is filtration. This process occurs in the renal corpuscle of the nephron in the kidneys, where blood plasma is filtered. During filtration, water and small molecules including salts, glucose, amino acids, urea, and microbes, can pass through the filter, while cells and proteins remain in the bloodstream. The filtered fluid, now called filtrate, eventually becomes urine, which carries any present microbes out of the urinary tract.