Kidney Microanatomy

(Sample Lesson)

Nephrons

Nephrons are microscopic structures that serve as the functional units of a kidney. Approximately 0.8 to 1.5 million nephrons are found in each kidney of a healthy adult.

A nephron is composed of a Bowman’s capsule and a renal tubule that extends from the capsule. The cup-like Bowman’s capsule is located in the cortex region of a renal lobe and surrounds a tuft of capillaries called a glomerulus. The capsule filters the blood as it passes through the glomerular capillaries and then passes the filtrate to the renal tubule. As the filtrate passes through the renal tubule, some substances are retained in the tubule, and others are returned to the bloodstream. The exchange process removes wastes and toxins, maintains fluid, electrolyte, and pH balances, and regulates blood pressure.

The renal tubule is divided into three sections, and each section performs a specific role in the exchange process. The first section, the proximal convoluted tubule (PCT), and the last section, the distal convoluted tubule (DCT), are located in the renal cortex. Connecting the PCT and DCT is the loop of Henle, which winds in and out of a medullary renal pyramid. A collecting duct carries the filtrate from the renal cortex to the apex (or papilla) of a pyramid, where it drains into a minor calyx.

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Some nephrons have a short loop of Henle that does not dip beyond the cortex. These nephrons are called cortical nephrons. About 15 percent of nephrons have long loops of Henle that extend deep into the medulla and are called juxtamedullary nephrons.

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Nephron Blood Supply

A series of large arteries carry blood to the renal lobes from the descending aorta. In the renal lobes, smaller arteries, arterioles, and capillaries deliver blood to the nephrons.

In the renal lobes, cortical radiate arteries (interlobular arteries) branch at right angles from the arcuate arteries that run alongside the bases of the renal pyramids. The cortical radiate arteries transport blood into the renal cortex.

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In the renal cortex, the cortical radiate arteries give off branches called afferent arterioles that deliver blood to the nephrons. Each afferent arteriole forms a tuft of high-pressure capillaries about 200 µm in diameter, called the glomerulus, which is enclosed by the Bowman’s capsule of a nephron. The glomerulus and the Bowman’s capsule together form the renal corpuscle. As blood passes through the glomerular capillaries, it is filtered. The interior of Bowman’s capsule collects the filtrate and then passes it to the renal tubules. After passing through the Bowman’s capsule, the glomerular capillaries merge to form a second arteriole called the efferent arteriole.

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The efferent arterioles deliver filtered blood to the peritubular capillaries, which wind around the renal tubules. Some of the peritubular capillaries extend into the renal medulla to form a network of capillaries called the vasa recta. The vasa recta capillaries are associated with the juxtamedullary nephrons, where they coil around the loop of Henle portions of the tubules. As blood flows through the peritubular and vasa recta capillaries, substances are exchanged with the nearby renal tubules, and the content of the filtrate is altered.

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Venules transport blood from the nephron capillaries to the cortical radiate veins, which then merge at right angles with the arcuate veins. The arcuate veins drain blood away from the renal lobes to the kidney’s major veins.

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Page Attributions

OpenStax College, Anatomy and Physiology

Access for free at – https://openstax.org/books/anatomy-and-physiology/pages/1-introduction

Reference: “Gross Anatomy of the Kidney“

Wikipedia, the free encyclopedia.

Reference 1: “Kidney“

Reference 2: “Nephron“