What proportion of nephrons are juxtamedullary, with long loops reaching deep into the medulla?

1. Most nephrons have a short loop of Henle that never leaves the cortex, and these are the cortical nephrons. 2. About 15 percent have long loops that dip deep into the medulla, and these are the juxtamedullary nephrons. 3. Those long loops are what build and sustain the concentration gradient of the medulla. 4. If the majority had long loops, the cortex would be far thinner than it is. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 25 "The Urinary System", section 25.3 Gross Anatomy of the Kidney_