The paired kidneys of mammals are organized into two layers, an outer layer called the cortex and a deeper layer, surrounded by the cortex, called the medulla (Fig. 41.15). Nephrons are organized into wedge-shaped renal pyramids (Fig. 41.15). Each nephron’s glomerulus is located within the renal cortex or outer layer of the medulla, and feeds into a renal tubule that starts in the renal cortex before dipping into the medulla at the base of the renal pyramid and then looping back up to the cortex. The collecting ducts of the renal tubules also descend into the pyramid’s base, emptying into the renal pelvis and draining through the ureter into the bladder.

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