The renal pyramids function as filtering and collections tubes for the transportation of urine. It is thought that the tissue of the kidney’s medulla contains a high concentration of sodium. As the collecting tubules travel through the medulla, the concentration of sodium causes water to be extracted through tubule walls into the medulla (the soft innermost part of an organ or structure).
This renal pyramid, as it is called, is also shaped like a grapefruit which has been cut in half to reveal the various sections partitioned by a thin membrane.The renal medulla is the soft part that filters the liquid waste from the blood cells that constantly feed this vital organ fresh oxygen.
The impurities are left behind in the renal medulla before being sent to the calyx located in the renal pelvis (a funnel-shaped interior structure of the kidney into which urine is discharged before passing into the ureter).
Urine is nothing more than the impurities found in the liquid parts of blood (plasma) that gets filtered through the kidneys renal medulla before it passes out of the body through the ureters, urinary bladder and then the urethra (the narrow tube which carries urine from the bladder to be discharged outside the body). The renal medulla of the kidney is surrounded by the renal cortex.
The tissues of the renal cortex dip into the medulla between adjacent renal pyramids to form a wall or renal columns. The granular appearance of the renal cortex is due to the random arrangement of tiny tubules associated to the nephrons, the functional part of the kidney.