In the renal system, peritubular capillaries are tiny blood vessels that travel alongside nephrons allowing reabsorption and secretion between blood and the inner lumen of the nephron. Peritubular capillaries surround the proximal and distal tubules, as well as the loop of Henle, where they are known as vasa recta.
Ions and minerals that need to be saved in the body are reabsorbed into the peritubular capillaries through active transport, secondary active transport, or transcytosis.
The ions that need to be excreted as waste are secreted from the capillaries into the nephron to be sent towards the bladder and out of the body.
Basically, they reabsorb useful substances such as glucose and amino acids and secrete certain mineral ions and excess water into the tubule.
The majority of exchange through the peritubular capillaries occurs because of chemical gradients, osmosis and Na+ pumps.