= 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.<Longitudinal section through Kidney by the Manipal Museum of Anatomy and Pathology>[specimenEXC002: cortex, medullary pyramids, columns and papillae]{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>.<Kidneys by the National Cancer Institute>[renal-pyramid organization and collecting ducts]{ref}
Back to article page
