The interstitium is composed of fibrocytes and occasional macrophages. The interstitial cells produce the extracellular matrix (collagen and glycosaminoglycans) , which surround the nephrons, duct, blood vessels, and lymphatics.
The vessels that are responsible for reabsorbing all of the molecules that cross the tubular epithelial cells are called peritubular capillaries. In order to do their job efficiently, they need to be immediately adjacent to the tubules. If there is an aggregate of fibroblasts or inflammatory cells, then it is more difficult for them to take up the products delivered to them by the tubular epithelial cells. Likewise, this intricate tortuous network of capillaries delivers oxygen and glucose to the tubules as well. Loss of the peritubular capillaries or an increase in the distance between the tubules and the capillaries will therefore impact tubular epithelial energy balance and functionality.
In addition to the peritubular capillaries that surround the cortical tubules, there is another aggregate of thin-walled vessels known as the vasa recta. These vessels run alongside the Loop of Henle.