11.4: Internal Anatomy of the Kidney

When dissected through a frontal section, the internal structure can be distinguished by an outer region called the renal cortex and an inner area termed the renal medulla (Figure 2). The renal medulla, in turn, consists of distinct sections known as renal pyramids, divided by connective tissue extensions termed renal columns that project from the cortex, traversing the medulla. These renal pyramids, resembling triangular wedges, possess a broader base bordering the cortex and a narrower apex referred to as the renal papilla. The papillae represent the termination point for several collecting ducts responsible for transporting urine, produced by nephrons, to the minor calyces, a segment of the urinary collection system (Figure 2).

The interplay between pyramids and renal columns creates kidney lobes. Multiple minor calyces converge to form major calyces, and these, in turn, merge to become renal pelvis, a more expansive cavity compared to each major calyx for the collection of urine. The ureters take on the role of funneling urine from the renal pelvis to the urinary bladder, thus facilitating the excretion of this waste from the body.

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Figure 2 | The Anatomy of the Left Kidney |​ ² This illustration depicts the internal and external structures of the kidney, highlighting its intricate vascular network and functional components. On the right, a cross-sectional view of the kidney reveals the distinct regions of the cortex and medulla. The cortex, the outer layer, contains renal corpuscles and is supplied by cortical blood vessels. The medulla, the inner region, features renal pyramids separated by renal columns. The pyramids terminate in papillae, which project into minor calyces. These minor calyces merge into major calyces, which in turn drain into the renal pelvis. The renal pelvis connects to the ureter, which carries urine to the bladder. The renal hilum, located on the medial side, serves as the entry and exit point for the renal artery, renal vein, renal nerve, and ureter.

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