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The collecting duct system of the kidney consists of a series of tubules and ducts that physically connect nephrons to a minor calyx or directly to the renal pelvis.The collecting duct participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and vasopressin (antidiuretic hormone).
The collecting duct system begins in the renal cortex and extends deep into the medulla. As the urine travels down the collecting duct system, it passes by the medullary interstitium which has a high sodium concentration as a result of the loop of Henle's countercurrent multiplier system. [1]: 67
The collecting ducts from each cluster of nephrons usually drain into an archinephric duct, which is homologous with the vas deferens of amniotes. However, the situation is not always so simple; in cartilaginous fish and some amphibians, there is also a shorter duct, similar to the amniote ureter, which drains the posterior (metanephric) parts ...
At this location, in the wall of the last portion of distal straight tubule, there is a modified region of tubular epithelium called the macula densa.(Fig. 5 in Kumaran and Hanukoglu 2020) [5] Cells in the macula densa respond to changes in the sodium chloride levels in the distal tubule of the nephron via the tubuloglomerular feedback (TGF) loop.
The renal papilla is the location where the renal pyramids in the medulla empty urine into the minor calyx in the kidney. Histologically it is marked by medullary collecting ducts converging to form a papillary duct to channel the fluid. Transitional epithelium begins to be seen.
To achieve such balance between water and ions, the loop of Henle coordinates its function with the collecting duct to regulate the amount of water to reabsorb or to excrete. While the loop of Henle makes the medulla of the kidney salty, the collecting duct regulates the permeability of water that could be reabsorbed to such salty environment.
The formation of urine begins within the functional unit of the kidney, the nephrons. Urine then flows through the nephrons, through a system of converging tubules called collecting ducts. These collecting ducts then join to form the minor calyces, followed by the major calyces that ultimately join the renal pelvis. From here, urine continues ...
The renal outer medullary potassium channel (ROMK) is an ATP-dependent potassium channel (K ir 1.1) that transports potassium out of cells. It plays an important role in potassium recycling in the thick ascending limb (TAL) and potassium secretion in the cortical collecting duct (CCD) of the nephron.