Renal pyramid

A renal pyramid is a roughly cone-shaped subdivision of the human renal medulla. Its broad base faces the renal cortex, while its tip forms a renal papilla directed toward a renal calyx. Its striated appearance reflects aligned tubular and vascular structures. Renal columns separate neighboring pyramids.^[ref]

A triangular profile in a longitudinal section should not be mistaken for a flat triangular organ. As an ideal geometric illustration, a cone of height $L$ and base radius $R$ has radius $r(z)=R(1-z/L)$ at distance $z$ from its base. Halfway to the tip, its cross-sectional area is $\pi R^2/4$, one quarter of the basal area. An actual renal pyramid is irregular, but the example explains how different cuts through a three-dimensional structure can produce very different profiles.

Many collecting ducts converge as they pass toward the renal papilla. Recognizing a renal pyramid therefore connects the gross shape of a dissected kidney with the direction of microscopic drainage. The pyramid contains numerous passages and surrounding tissue; it is not one enlarged nephron.^[ref]