Nierenmarks

Nierenmarks, also known as the renal medulla, describe the inner portion of the kidney. It lies beneath the renal cortex and surrounds the renal pelvis, extending from the corticomedullary junction to the papillae. The medulla is organized into renal pyramids that project toward the calyces and are separated by renal columns (columns of Bertin). Each pyramid ends at a renal papilla, through which urine drains into minor calyces and onward to major calyces and the renal pelvis. The medulla contains the loops of Henle, the collecting ducts, and the vasa recta, and is functionally divided into outer and inner medullary regions.

Functionally, the medulla plays a central role in concentrating urine. The loop of Henle and the collecting ducts establish and maintain an osmotic gradient in the interstitium, enabling water reabsorption from the collecting ducts under antidiuretic hormone control. The vasa recta preserve this gradient as blood perfuses the medulla in a countercurrent arrangement.

Clinical notes: Alterations of the medulla can affect urine concentration and may occur in certain diseases. Medullary necrosis, medullary sponge kidney, and nephrocalcinosis involve the medullary region. Ischemic injury or prolonged analgesic use can also impact medullary tissue and the kidney’s concentrating ability.