Within each renal lobe are hundreds of thousands of nephrons, the function unit of the kidney. Each nephron originates in the cortex, at the renal corpuscle associated with glomerular capillaries. Extending from the corpuscle is the proximal convoluted tubule, then the nephron loop (of Henle) into the medulla and back to the cortex, then the distal convoluted tubule and collecting tubule which merges into a collecting duct for urine transport to the calyx. All nephrons are located completely within the cortex except for their medullary loops. Juxtamedullary nephrons usually have much longer loops than cortical nephrons. Each kidney contains 1–1.4 million functional units called nephrons (Figure 2). The major divisions of each nephron are:
Renal corpuscle, an initial dilated portion in the cortex
Proximal convoluted tubule, located primarily in the cortex
Thin and thick limbs of the nephron loop (loop of Henle), which descend into the medulla, then ascend back to the cortex
Distal convoluted tubule
Collecting tubules from several nephrons converge into collecting ducts which carry urine to the calyces and the ureter. Cortical nephrons are located almost
completely in the cortex while juxtamedullary nephrons close to the medulla have long loops in the medulla (Figure 2).