Pars convoluta

The proximal tubule is the specific target for several antibiotics, mycotoxins, certain antineoplastic drugs, and heavy metals. The proximal tubule can be divided into three discrete segments. The SI segment (pars convoluta) is the initial portion of the proximal convoluted tubule S2 is the transition between the pars convoluta and the pars recta, which consists of the end of the convoluted segment and initial portion of the straight segment and S3 (pars recta)... 

The cell structure of the pars recta, less complex than that seen in the cells associated with the pars convoluta, is characterized by a decrease in the size and number of mitochondria. As such, the pars recta, in comparison with pars convoluta, is less involved in functions requiring active transport, such as sodium and water reabsorption. 

The ascending thick limb or the pars recta of the distal tubule leads into the distal convoluted tubules or the pars convoluta of the distal tubule. The macula densa is a specialized region corresponding to the initial portion of the pars convoluta of the distal tubule. The two segments of the distal tubule (the pars recta and pars convoluta) are similar morphologically and functionally in terms of active chloride transport and permeability to water. 

Proximal convolution Pars, , convoluta Proximal Proximal convoluted tubule segment (PCT) 51 cells 52 cells 53 cells P1 segment P2 segment P3 segment... 

Distal convolution Pars convoluta Distal convoluted DCT1 tubule (DCT) qct2 DCT cells (+ 1C cells) Early distal tubule Distal tubule... 

The proximal tubules are divided into the convoluted section the pars convoluta and the straight portion of the tubule descending into the medulla, the pars recta. The pars recta is sometimes referred to as the S3 segment of the proximal tubules the other two segments, SI and S2, form the convoluted part of the tubule. 

Proximal Convoluted Tubule = Proximal Convolution = Pars Convoluta of Proximal Tubule = Convoluted Part of Proximal Tubule... 

Pars Convoluta of Distal Tubule Convoluted Part of Distal Tubule... 

Renal transports of urate in the mammalian kidney have a common characteristic feature a secretory and a re absorptive transport oppose each other in the proximal tubule. The proximal tubule (pars convoluta and pars recta) plays the major role in urate transport. The secretory and the reabsorptive transports may be inhibited by the same drugs, the concentrations needed to inhibit one or the other differing in the different species. The secretory transport of urate may involve different carriers in different species. Further studies are needed to determine the role of the peritubular site versus the luminal site of the cells in the reabsorptive and the secretory transports and to characterize the carriers involved. 

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