The collection of capillaries where plasma leaks out to begin the filtration process form a .

Filtration begins in the glomerulus, a cluster of tiny capillaries inside the nephron. Blood pressure pushes water and small dissolved substances from these capillaries into the surrounding capsule, while blood cells and most proteins remain in the blood. The renal medulla is a kidney region, and the renal vein carries blood away from the kidney.

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