Base of renal pyramid

The base of the renal pyramid refers to the broad, outer portion of each renal (medullary) pyramid that faces toward the renal cortex. The renal pyramids are cone-shaped structures within the renal medulla, and each pyramid has two distinct ends:

• Base (outer border): This is the wide end of the pyramid, oriented toward the outer cortex of the kidney. It borders the corticomedullary junction, where the cortex and medulla meet. The medullary rays (extensions of the pyramid) project from the base into the cortex. The base receives the straight portions (pars recta) of the proximal and distal tubules, as well as the descending and ascending limbs of the loops of Henle and the collecting ducts as they course between the cortex and medulla.

• Apex (renal papilla): In contrast, the narrow, inner tip of the pyramid points toward the renal hilum and projects into a minor calyx. This is where the collecting ducts converge and open at the area cribrosa to drain urine into the collecting system.

Key anatomical relationships of the base:

• It is capped by a layer of cortical tissue (the cortical arch or cortex corticis).

• The interlobular arteries and veins run along the base at the corticomedullary junction (arcuate vessels).

• Columns of Bertin (renal columns), which are extensions of cortical tissue, separate adjacent pyramids and extend inward from the base region.

Each human kidney typically contains 8-18 renal pyramids, and the base of each pyramid serves as the functional interface between the cortex (where filtration occurs in the glomeruli) and the medulla (where urine concentration takes place).