- The nephron is the fundamental functional unit of the kidney and can be thought of as a long tube of variable thickness which winds a set path through the kidney. Most of the macroscopic physiological function of the kidney is simply the result of the combined action of nearly a million individual nephronic units. The nephron can be subdivided into several sections based on their distinct anatomic appearance and location. In general, these anatomic sections play distinct functional roles although the boundaries between functional segments of the nephron do not precisely align with anatomic features. Below we list the anatomic sections of the nephron, describe their appearance and location, and also highlight functional boundaries. Additionally, several different anatomic subtypes of nephrons exist which we describe in the final section.
- The glomerulus is a small, spherical structure at the center of which lies a tuft of glomerular capillaries surrounded by the membranous Bowman's Capsule.
- The Bowman's Capsule is continuous with the proximal tubule and collects any fluid filtering through the glomerular capillaries and directs it into the remainder of the nephron.
- Proximal Tubule:
- The proximal tubule lies within the renal cortex and is the section of nephron immediately after the glomerulus. The entire proximal tubule possesses a distinct physiological function and charts a convoluted, twisting path and is often termed the "Proximal Convoluted Tubule".
- Loop of Henle:
- The loop of Henle is the section of nephron lying after the proximal tubule and dips down into the renal medulla. Henle's loop displays variable thickness with the entire descending arm and the lower portion of the ascending arm being quite thin, together known as the Thin Loop of Henle. In contrast, the upper portion of the ascending arm is thick and is known as the Thick Ascending Loop of Henle. As suggested by their distinct anatomical and histological appearance the thin and thick segments of Henle's loop display different functionalities. At the end of the thick ascending loop of Henle there is a blister of tissue known as the Macula Densa which is part of the Juxtaglomerular Apparatus.
- Distal Tubule:
- The distal tubule follows the loop of Henle and lies within the renal cortex. Like the proximal tubule, the distal tubule charts a convoluted, twisting course and is sometimes termed the Distal Convoluted Tubule. The early distal tubule possesses a distinct functionality than its late portion. The late distal tubule functions in concert with the collecting duct and thus these segments are often termed the Late Distal Tubule and Collecting Duct.
- Collecting Duct
- The collecting duct lies after the distal tubule and dips back into the renal medulla. The end of the collecting duct exists at the renal papillae and any remaining nephronic fluid (now considered urine) into the minor calyces. As mentioned, the collecting duct and the late distal tubule share a similar function and are thus grouped under the heading of Late Distal Tubule and Collecting Duct.
|Anatomical Nephron Subtypes|
- There are two basic anatomical subtypes of nephrons depending on the length of the loop of Henle.
- Cortical Nephron:
- Have short loops of Henle that do not dip far into the renal medulla. They do not contain vasa recta.
- Juxtamedullary Nephrons:
- Have long loops of Henle that dip far into the renal medulla. These long loops of Henle are accompanied by vasa recta. Juxtamedullary nephrons are the nephrons primarily responsible for generating the Corticopapillary Osmotic Gradient.