The renal pyramids, also known as malpighian pyramids, are located inside the inner kidney. They consist of tubules, which collect urine from the outer kidneys and transfer them to the calyces, which store urine before it passes to the ureter and bladder.
Renal pyramids are conically shaped, and the point of each, called the papilla, leads into a calyx. The papilla allows urine to pass through its porous membrane in small droplets. The openings are connected to the duct of Bellini, where all the tubules of the renal pyramids converge. Between each pyramid runs a series of large arteries called the interlobar arteries. If one of these arteries become blocked, the renal pyramids can become seriously damaged.
The renal pyramids are atop parallel nephrons, giving the structure a striped appearance. Nephrons are the basic unit of the kidney that produce urine as they filter waste from the blood. Nephrons also regulate water levels and soluble substances, such as sodium, in the blood stream. Once the blood is filtered, unneeded compounds are excreted as waste, and the rest is reabsorbed into the bloodstream. The number of renal pyramids contained within the kidney varies from creature to creature. Humans have seven pyramids in each kidney, while smaller animals, such as rats and rabbits, only have one.