Ninety percent of the filtered sodium, chloride and water is reabsorbed by the proximal tubule, loop of Henle
, and early distal tubule.
Two different types of nephrons receive output from the proximal tubule, conduct it through the medullary layer via the loop of Henle, and pass it on to the distal convoluted tubule.
Upon exit from the loop of Henle, tubule fluid enters the distal convoluted tubule (DCT) in the cortical layer.
In healthy individuals, the Aquaporin-1 channels remain an ever-present structure in the luminal wall cells of the proximal tubule and the descending limb of the loop of Henle.
The dilute fluid exiting the loop of Henle remains hypotonic all the way to the final urine.
Vasopressin also increases urea permeability in the collecting duct within the inner medullary layer and increases the rate of active NaCl absorption from the loop of Henle.
The distal nephron, including all subsegments between the thin descending limb of the loop of Henle and the inner-medullary collecting tubule, is the site of fine-tune regulation of all solutes and water that leave the proximal tubule.
The loop of Henle is the next component of the tubular system and consists of the thin descending limb, thin ascending limb, and thick ascending limb.
The initial section of the DT immediately after the thick ascending limb of the loop of Henle contains specialized cells, the macula densa cells, which are a component of the juxtaglomerular apparatus.
As the ascending limb of the loop of Henle moves upward, the initial portion of the DT passes between the afferent and efferent arterioles that proceed or form from, respectively, the glomerulus of that nephron.