Proximal tubule
Proximal tubule | |
---|---|
Metanephric blastema | |
Identifiers | |
Latin | tubulus proximalis, pars tubuli proximalis |
MeSH | D007687 |
Anatomical terminology] |
The proximal tubule is the segment of the nephron in kidneys which begins from the renal pole of the Bowman's capsule to the beginning of loop of Henle. At this location, the glomerular parietal epithelial cells (PECs) lining bowman’s capsule abruptly transition to proximal tubule epithelial cells (PTECs). The proximal tubule can be further classified into the proximal convoluted tubule (PCT) and the proximal straight tubule (PST).
Structure
The most distinctive characteristic of the proximal tubule is its luminal brush border.[citation needed]
Brush border cell
This section needs additional citations for verification. (February 2021) |
The luminal surface of the
The
Cuboidal epithelial cells lining the proximal tubule have extensive lateral interdigitations between neighboring cells, which lend an appearance of having no discrete cell margins when viewed with a light microscope.
This has led some observers to describe the lumen of proximal tubules as occluded or "dirty-looking", in contrast to the "clean" appearance of
Divisions
Based on its appearance at low magnification, the proximal tubule can be divided into two sections: the proximal convoluted tubule (PCT), and the proximal straight tubule (PST).[3] Differences in cell outlines exist between these segments, and therefore presumably in function too.[citation needed]
Based on ultrastructure, it can be divided into three segments, S1, S2, and S3.
Segment | Gross divisions | Ultrastructure divisions | Description |
---|---|---|---|
Proximal tubule | convoluted | S1[4] | Higher cell complexity[4] |
S2[4] | |||
straight | |||
S3[4] | Lower cell complexity[4] |
Proximal convoluted tubule (pars convoluta)
The pars convoluta (Latin "convoluted part") is the initial convoluted portion.[citation needed][5]
In relation to the morphology of the kidney as a whole, the convoluted segments of the proximal tubules are confined entirely to the renal cortex.[citation needed]
Some investigators on the basis of particular functional differences have divided the convoluted part into two segments designated S1 and S2.[citation needed]
Proximal straight tubule (pars recta)
The pars recta (Latin "straight part") is the following straight (descending) portion.[citation needed][5]
Straight segments descend into the outer medulla. They terminate at a remarkably uniform level and it is their line of termination that establishes the boundary between the inner and outer stripes of the outer zone of the renal medulla.[citation needed]
As a logical extension of the nomenclature described above, this segment is sometimes designated as S3.[citation needed]
Functions
Absorption
The proximal tubule efficiently regulates the pH of the filtrate by secreting hydrogen ions (acid) into the tubule and reabsorbing approximately 80% of the filtered bicarbonate.[6]
Fluid in the filtrate entering the proximal convoluted tubule is reabsorbed into the
Sodium reabsorption is primarily driven by this
Substance | % of filtrate reabsorbed | Comments |
water | approximately two-thirds | Mass movement of water and occurs both through the cells and between them, paracellular ).
|
sodium | approximately two-thirds | Mass movement of sodium occurs through the cells, by secondary active transport on the apical membrane, followed by active resorption across the basolateral membrane via the isotonically , in that the osmotic potential of the fluid leaving the proximal tubule is the same as that of the initial glomerular filtrate.
|
organic solutes (primarily glucose and amino acids) | 100% | co-transporters driven by the sodium gradient out of the nephron.
|
potassium | approximately 65% | Most of the filtered potassium is resorbed by two paracellular mechanisms – solvent drag and simple diffusion.[11] |
urea | approximately 50% | Paracellular fluid reabsorption sweeps some urea with it via solvent drag. As water leaves the lumen, the concentration of urea increases, which facilitates diffusion in the late proximal tubule.[11][page needed] |
phosphate | approximately 80% | intestine and bones into the blood, the responses to PTH cancel each other out, and the serum concentration of phosphate remains approximately the same.
|
citrate |
70%–90%[12] | Acidosis increases absorption. Alkalosis decreases absorption. |
Secretion
Many types of
Most of the
Clinical significance
Proximal tubular epithelial cells (PTECs) have a pivotal role in kidney disease. Two mammalian
Cancer
Most renal cell carcinoma, the most common form of kidney cancer, arises from the convoluted tubules.[15]
Other
PTECs also participate in the progression of tubulointerstitial injury due to
See also
Additional images
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Distribution of blood vessels in cortex of kidney.
-
Glomerulus.
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TEM of negatively stained proximal convoluted tubule of Rat kidney tissue at a magnification of ~55,000x and 80KV with Tight junction.
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Renal corpuscle
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Diagram outlining movement of ions in nephron.
References
This article incorporates text in the public domain from page 1223 of the 20th edition of Gray's Anatomy (1918)
- S2CID 42761720.
- PMID 31605441.
- ISBN 978-0-323-42796-8.
- ^ ISBN 978-1-4160-2328-9.
- ^ ISBN 978-1-4698-8931-3.
- ^ S2CID 3122791.
- S2CID 24141102.
- PMID 27214555.
- S2CID 29602556.
- ISBN 978-1461437840.
- ^ a b Boron WF, Boulpaep EL, eds. (2005). Medical Physiology (Updated ed.).[page needed]
- ^ Hypocitraturia~overview#aw2aab6b5 at eMedicine
- ^ ISBN 978-0-683-07354-6.
- )
- S2CID 28183020.
External links
- Anatomy photo: Urinary/mammal/cortex1/cortex6 - Comparative Organology at University of California, Davis – "Mammal, kidney cortex (LM, Medium)"
- Nosek, Thomas M. "Section 7/7ch03/7ch03p14". Essentials of Human Physiology. Archived from the original on 2016-03-24. – "The Nephron: Proximal Tubule, Pars Convoluta & Pars Recta"
- UB, and UF) turinary/urinhaute02