In the nephron, uric acid is secreted through

Ultrafiltration occurs at the barrier between the blood and the filtrate, in the renal corpuscle or Bowman's capsule in the kidneys. The Bowman's capsule contains a dense capillary network called the glomerulus. Blood flows into these capillaries through a wide afferent arteriole and leaves through a narrower efferent arteriole. The high pressure forces small molecules, such as,  water, glucose, amino acids, sodium chloride and urea,  through the filter, from the blood in the glomerular capsule across the basement membrane of the Bowman's capsule,  and into the nephron. This type of high pressure filtration is ultrafiltration. The fluid formed in this way is called glomerular filtrate.