Why is the convoluted tubule long

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List of terms related to Distal convoluted tubule. Editor-In-Chief: C. Michael Gibson, M. The distal convoluted tubule DCT is a portion of kidney nephron between the loop of Henle and the collecting duct system. It is partly responsible for the regulation of potassium , sodium , calcium , and pH.

The distal convoluted tubule DCT is the final segment of the nephron. It is lined with simple cuboidal cells that are shorter then those of the PCT. DCT can be recognized by its numerous mitochondria , basal infoldings and lateral membrane interdigitations with neighboring cells.

The cells stain more palely than those of the proximal convoluted tubule. The epithelium of these tubules consist of cuboidal or columnar cells. They empty into collecting ducts that are easy to recognise, because they have large lumens, with pale staining columnar epithelium.

From these descriptions, try to find renal corpuscles , proximal and distal convoluted tubules and loops of Henle in this eMicroscope section of the cortex from the kidney. This image may also be viewed with the Zoomify viewer. After leaving the renal corpuscle , the filtrate passes through the renal tubule in the following order, as shown in the diagram: proximal convoluted tubule red: found in the renal cortex loop of Henle blue: mostly in the medulla distal convoluted tubule purple: found in the renal cortex collecting tubule black: in the medulla collecting duct black: in the medulla.

In short:. The specifics of that acid-base manipulation here will be left for another chapter, but, in order to simplify revision, one may be reminded that the proximal tubule is where brush border carbonic anhydrase is responsible for the reabsorption of bicarbonate, which it converts into CO 2.

This is the step susceptible to pharmacological manipulation by acetazolamide , and the site of type 2 renal tubular acidosis :. The co-transport of sodium out of the tubule lumen decreases tubular fluid osmolality, as compared to that of extraluminal fluid.

This produces a net movement of water out of the tubule, by all sorts of pathways. Some movement is paracellular through the supposedly tight junctions and some is facilitated by aquaporins in the apical membrane.

As the result of this, the tubular fluid remains iso-osmolar over the length of the proximal tubule. The net effect of all this is on the composition of the tubular fluid is best described by this relatively famous graph from Rector :. The reason for the relative increase in tubular chloride concentration is largely the need to maintain electroneutrality, as other anionic solutes amino acids, bicarbonate are extracted and there is a net loss of negative charge.

Additionally, absorption of large solutes occurs by vesicle-mediated pinocytosis in the proximal convoluted tubule. This is how stray protein and albumin is usually cleared from the proximal tubule fluid. The numerous endosomes seen in these tubular cells are full of this debris. Unlike the heavily brush-bordered convoluted segment, this part of the tubule is mainly concerned with the elimination of things which might not have been filtered particularly well at the glomerulus, but which are nonetheless important to be rid of.

This is the site of active secretion for many xenobiotic molecules, such as drugs and heavy metals. It is also the part of the nephron which is most easily damaged by various "nephrotoxins". OAT-4 at the apical membrane then ejects these unwanted substances into the tubular fluid. Curthoys, Norman P. Welling, Larry W. Harris, C. Zhai, Xiao-Yue, et al. Doucet, A. Doucet, Alain. Ernst, Stephen A.