Peritubular capillaries are a network of capillaries (tiny blood vessels) which surround the renal tubules of the nephrons, allowing reabsorption and secretion between blood and the inner lumen of the nephron.
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. The majority of exchange through the peritubular capillaries takes place because of chemical gradients, osmosis and Na+ pumps.
The kidney has two capillary beds arranged in series, the glomerular capillaries which are under high pressure for filtering, and the peritubular capillaries which are situated around the tubule and are at low pressure, allowing large volumes of fluid to be filtered and reabsorbed.