Renal pyramid
Pyramis renalis
Also known as: medullary pyramid, Malpighian pyramid
A cone-shaped, striated mass of medullary tissue whose base faces the cortex and whose apex (papilla) drains urine into a minor calyx.
Overview
Each kidney has ≈8–18 renal pyramids. The base borders the cortex at the corticomedullary junction, where the arcuate vessels run; the apex narrows into the renal papilla. The striations visible to the naked eye are bundles of loops of Henle, collecting ducts and vasa recta running parallel toward the papilla, and they continue into the cortex as medullary rays.
A pyramid plus its covering cap of cortex and half of each adjacent renal column forms a renal lobe, the developmental unit of the kidney; fetal lobation can persist as surface grooves in adults.
- Location
Renal medulla, between the renal columns, apices pointing toward the renal sinus.
Anatomy
- Histology
Thin and thick limbs of loops of Henle, collecting ducts lined by cuboidal → columnar principal and intercalated cells, vasa recta bundles.
Function
- House the medullary segments of nephrons and collecting ducts that concentrate urine
- Funnel urine toward the papilla
Clinical significance
Fetal lobulation
Persistent surface lobulation corresponding to pyramids is a normal variant on imaging and must not be mistaken for scarring (scars overlie calyces; fetal lobulation notches lie between pyramids).
Compiled from standard anatomy and physiology references — see the Urinary System sources. For education only; not medical advice.