肾单位

A nephron comprises the renal corpuscle and renal tubule. The renal corpuscle contains the glomerulus, a capillary network, and Bowman's capsule, a double-walled epithelial cup where blood plasma filtration occurs. The renal tubule receives the filtered fluid and consists of three sections: the proximal convoluted tubule, loop of Henle, and distal convoluted tubule.

Each kidney contains approximately 1 million nephrons. The renal corpuscle and convoluted tubules are located in the renal cortex, while the loop of Henle extends into the renal medulla. About 80 to 85 percent of nephrons are cortical nephrons in the outer cortex with shorter loops, while 15 to 20 percent are juxtamedullary nephrons positioned deeper in the cortex near the medulla with longer loops.

Bowman's capsule is a double-walled epithelial structure surrounding the glomerulus where blood plasma filtration occurs. The filtered fluid, called glomerular filtrate, transfers from Bowman's capsule into the renal tubule for further processing. This structure is essential for initiating the filtration process that begins urine formation.

Cortical nephrons comprise 80 to 85 percent of nephrons and feature shorter loops of Henle that remain mostly in the cortex. Juxtamedullary nephrons, representing 15 to 20 percent, are located deeper in the cortex near the medulla and have longer loops extending far into the medulla. Their longer loops enable the kidney to produce urine of varied concentrations through reabsorption and secretion in the loop of Henle.

The renal tubule receives glomerular filtrate from Bowman's capsule and processes it through three sections: the proximal convoluted tubule, loop of Henle, and distal convoluted tubule. These segments perform reabsorption and secretion to modify the filtrate composition. The distal convoluted tubules empty into collecting ducts that eventually drain into the minor calyces.

Long nephron loops, found in juxtamedullary nephrons, extend deep into the renal medulla and are critical for the kidney's ability to produce urine of varying concentrations. These loops receive blood from both peritubular capillaries and vasa recta, enabling efficient solute and water reabsorption. The thin ascending limb of long loops has a slimmer epithelial layer that facilitates selective reabsorption.

The loop of Henle connects the proximal convoluted tubule to the distal convoluted tubule and consists of a descending limb that dips into the renal medulla and an ascending limb that returns to the renal cortex. In juxtamedullary nephrons, the ascending limb has thin and thick segments. This U-shaped structure enables the kidney to concentrate or dilute urine based on body needs.