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In response to decreased flow of tubular fluid in the thick ascending limb / decreased salt concentration at the macula densa: Reduced filtration at the glomerulus or increased reabsorption of sodium and water by the Proximal Convoluted Tubule causes fluid in the tubule at the macula densa to have a reduced concentration of sodium chloride.
Reabsorption allows many useful solutes (primarily glucose and amino acids), salts and water that have passed through Bowman's capsule, to return to the circulation. These solutes are reabsorbed isotonically , in that the osmotic potential of the fluid leaving the proximal convoluted tubule is the same as that of the initial glomerular filtrate.
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).
This filtrate then flows along the length of the nephron, which is a tubular structure lined by a single layer of specialized cells and surrounded by capillaries. The major functions of these lining cells are the reabsorption of water and small molecules from the filtrate into the blood, and the secretion of wastes from the blood into the urine.
excretion = (filtration + secretion) - reabsorption; The proximal convoluted tubule of the nephron has protein channels that reabsorb glucose, and others that secrete para-aminohippuric acid (PAH). However, its ability to do so is proportionate to the channel proteins available for the transport. [citation needed]
The processes of blood plasma filtration, tubular reabsorption and tubular secretion occur in the kidneys, and urine formation is a result of these processes. [8] The kidneys produce renin [32] and erythropoietin [33] hormones, and are involved in the conversion of vitamin D to its active form. [34]
The DCT is lined with simple cuboidal cells, the distal convoluted tubule cells, that are shorter than those of the proximal convoluted tubule (PCT). The lumen appears larger in the PCT than the DCT lumen because the PCT has a brush border (microvilli).
The presence of aquaporin-1 channels in the thin segment facilitates high water permeability, crucial for water reabsorption as part of the kidney's countercurrent exchange mechanism. [ 4 ] [ 5 ] They can be distinguished from the vasa recta by the absence of blood, and they can be distinguished from the thick ascending limb by the thickness of ...