Nephron Structure and Function

The nephron is the functional unit of the kidney: each one carries out filtration, reabsorption, and secretion to form urine. It comprises a renal corpuscle (glomerulus plus Bowman's capsule), where plasma is filtered, and a tubule that progressively modifies the filtrate as it passes toward the collecting duct.

Definition

A nephron is the microscopic functional unit of the kidney, consisting of a renal corpuscle that filters plasma and a continuous tubule that selectively reabsorbs and secretes solutes and water to produce urine.

Scope

This entry describes the segmental organization of the nephron — renal corpuscle, proximal tubule, loop of Henle, distal convoluted tubule, and connecting segment — and how this structure maps onto its physiological tasks. It introduces cortical and juxtamedullary nephrons and the cells of the glomerulus, while deferring the detailed mechanics of the filtration barrier, GFR, and tubular transport to dedicated entries.

Core questions

• What are the segments of the nephron and what does each contribute?
• How does the renal corpuscle initiate urine formation?
• How do cortical and juxtamedullary nephrons differ?
• Which specialized cells make up the glomerulus?

Key concepts

• Renal corpuscle (glomerulus and Bowman's capsule)
• Proximal convoluted tubule
• Loop of Henle
• Distal convoluted tubule and connecting tubule
• Cortical versus juxtamedullary nephrons
• Podocytes, mesangial cells, and the juxtaglomerular apparatus

Mechanisms

Blood enters each glomerulus through an afferent arteriole and is filtered across the capillary tuft into Bowman's space, the first step of urine formation (brenner-1971). The resulting filtrate flows into the proximal tubule, then the loop of Henle, the distal convoluted tubule, and the connecting tubule before joining a collecting duct. Along this path the tubular epithelium reabsorbs most filtered water and solutes and secretes selected substances, so that the final urine differs greatly from the initial filtrate. Within the glomerulus, podocytes wrap the capillaries and form the slit diaphragm, mesangial cells provide structural support, and the juxtaglomerular apparatus links tubular flow to vascular control (pavenstadt-2003). The classical clearance framework that interprets these functions was set out by Smith (smith-1951).

Clinical relevance

Because the nephron is where filtration and tubular processing occur, its structure underlies how clinicians conceptualize kidney function and the level at which many kidney disorders are localized. This entry describes normal structure and function for reference; it does not provide diagnostic criteria or treatment guidance.

Evidence & guidelines

The descriptions here draw on classical renal physiology (smith-1951), micropuncture studies that quantified single-nephron filtration (brenner-1971), and reviews of glomerular cell biology (pavenstadt-2003).

History

Understanding of the nephron developed from nineteenth- and twentieth-century microanatomy and was placed on a quantitative physiological footing by clearance methods that allowed renal function to be measured in the intact organism (smith-1951). Micropuncture techniques later made it possible to sample fluid from individual nephron segments and measure single-nephron filtration directly (brenner-1971).

Key figures

• Homer W. Smith
• Barry M. Brenner
• Wilhelm Kriz

Seminal works

• smith-1951
• brenner-1971
• pavenstadt-2003

Frequently asked questions

What is the functional unit of the kidney?

The nephron. Each kidney contains roughly a million nephrons, and each one independently filters plasma and processes the filtrate to form urine.

What are the two main parts of a nephron?

The renal corpuscle (the glomerulus and surrounding Bowman's capsule), where filtration occurs, and the tubule, which reabsorbs and secretes solutes and water as it carries the filtrate toward the collecting duct.