Kidney: Nephron and juxtaglomerular apparatus

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The nephron is the main functional unit of the kidney, responsible for removing metabolic waste and excess water from the blood. Depending on their distribution and morphology, there are two main types of nephrons in the kidney: cortical and juxtamedullary. 

The renal corpuscle is the filtration apparatus of the nephron. Each corpuscle consists of two main elements; the glomerulus and glomerular (Bowman's) capsule.

• The glomerulus is a network of capillaries formed by branches of the renal artery (afferent and efferent arterioles). 

• The glomerular capsule surrounds the glomerulus. It consists of two layers (parietal and visceral), which bound a cavity called the glomerular capsular space (Bowman’s / urinary space). The inner visceral layer is made of special cells called podocytes. The outer parietal layer is made of simple squamous epithelium and is continuous with the nephron tubules. The afferent and efferent arterioles enter the renal corpuscle at the vascular pole, while the site where the glomerular capsule narrows and continues as the proximal thick segment of the nephron is called the urinary pole.

The renal tubule consists of the proximal tubule, nephron loop (of Henle), distal tubule and connecting tubule. The urine from the renal tubules of several adjacent nephrons flows together into a collecting duct which drains into the caliceal system of the renal pelvis.

At the vascular pole of the renal corpuscle are a collection of cells called the juxtaglomerular apparatus (JGA). This is formed by 3 types of cells: macula densa, juxtaglomerular granular (JG) cells and extraglomerular mesangial (Lacis) cells.

Watch the following video to learn more about the histological appearance of the kidney. (note: this video also covers topics related to the previous study unit, Kidney: Cortex, medulla and pelvicalyceal system)

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