Collecting duct

A branching kidney tubule that receives fluid from nephrons and carries it toward the renal pelvis. Its water and solute permeability helps determine final urine concentration.

Antidiuretic hormone: A hormone that increases water reabsorption by making collecting-duct cells more permeable to water. It inserts aquaporin channels into duct cells, allowing water to leave the tubular fluid.
Nephron: The kidney’s microscopic functional unit, consisting of a renal corpuscle and a tubule that processes filtrate. Nephrons deliver their processed fluid into the collecting system.
Urine concentration: The process of producing urine with a solute concentration adjusted to the body’s water balance. Collecting ducts determine how much water remains in urine after nephron processing.
Nephron loop: The U-shaped portion of a nephron that descends into the medulla and returns toward the cortex. Unlike the collecting duct, it is part of an individual nephron and helps establish the medullary gradient.
Aquaporin 2: A water-channel protein inserted into the apical membrane of collecting-duct principal cells in response to antidiuretic hormone. Its regulated insertion provides the duct’s adjustable route for water reabsorption.
Glomerulus: A tuft of capillaries where blood pressure drives filtration into the nephron. It begins the fluid pathway that ultimately reaches the collecting duct.
Diabetes insipidus: A disorder causing excessive dilute urine because antidiuretic hormone is deficient or the kidneys respond poorly to it. Impaired hormone action at collecting ducts prevents adequate water reabsorption.
Renal pelvis: The funnel-shaped chamber that collects urine from the kidney’s calyces and directs it into the ureter. It lies downstream of collecting ducts, which drain through papillae into the calyces.
Principal cell: An epithelial cell of the collecting duct that reabsorbs sodium and water and secretes potassium. These cells mediate hormone-controlled water and electrolyte handling in the duct.
Proximal tubule: The nephron segment that reabsorbs most filtered water and solutes after glomerular filtration. Its fluid passes through later nephron segments before entering collecting ducts.

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