nefroni

The nefroni are the microscopic, functional units of the kidney responsible for producing urine. Each nefrone (singular nephron) filters blood, reclaims useful substances, and forms waste-containing urine. In healthy adult humans, the kidneys contain roughly 1 to 2 million nefroni per organ.

A typical nefrone consists of two main components: the renal corpuscle and the tubular system. The renal corpuscle includes the glomerulus, a tuft of capillaries, and surrounding Bowman's capsule. Blood filtration occurs across a filtration barrier formed by fenestrated endothelium, a basement membrane, and podocyte foot processes. The resulting filtrate enters Bowman's space and proceeds into the tubular system.

The tubular system comprises the proximal tubule, the loop of Henle (descending and ascending limbs), the distal tubule, and the collecting duct. The proximal tubule reabsorbs most filtered water and nutrients (such as glucose and amino acids) and secretes certain wastes. The loop of Henle establishes a osmotic gradient essential for concentrating urine. The distal tubule and collecting duct fine-tune reabsorption of ions and water under hormonal control, contributing to body fluid and electrolyte balance.

Nephroni receive blood via the afferent arteriole and drain via the efferent arteriole, with surrounding peritubular capillaries and, in juxtamedullary nefroni, vasa recta supporting reabsorption and solute transport. Two major nefron types exist: cortical nefroni, with short loops of Henle, and juxtamedullary nefroni, with long loops critical for concentrating urine.

Regulation, development, and disease influence nephron number and function, playing a central role in overall kidney health and fluid homeostasis.