When a kidney is cut lengthwise, three distinct regions become apparent. the outer region is light in color, while the deeper "middle" region is darker reddish-brown. the inner deepest region is flat and tube-like?

In the cross-section of a kidney, there are three main regions that become apparent. The outer region is called the "renal cortex", this is where the capillaries are mainly located. The deeper and darker region, that looks like small pyramids arranged in a semicircle is called the "renal medulla", where the filtering of the blood takes place. The flat, tube-like structure is called the "renal pelvis".