Final answer:
The peritubular capillaries are the tiny vessels that surround the tubules in the kidney, which include the proximal and distal convoluted tubules and are associated with the vasa recta.
Step-by-step explanation:
The tiny vessels that surround the tubules in the kidney are called peritubular capillaries. These capillaries form a second capillary bed of the renal portal system and are primarily associated with the proximal and distal convoluted tubules, as well as with the vasa recta in juxtamedullary nephrons. In the kidney structure, first, the blood gets filtered in Bowman's capsule which is closely associated with the glomerulus; then the filtered fluid enters the proximal convoluted tubule (PCT), moves down the descending and up the ascending limbs of the loop of Henle before finally arriving in the distal convoluted tubule (DCT). The DCT empties into collecting ducts that eventually lead to the renal pelvis and ureter.