Quick Facts
The proximal convoluted tubule is the most proximal part of the renal tubule, extending from the glomerular capsule to the proximal straight tubule (Dorland, 2011).
Structure and/or Key Features
The proximal convoluted tubule describes the early part of the proximal tubule that has a twisted appearance. It measures approximately 14 mm in length and 60 µm in diameter. (Martini, Nath and Bartholomew, 2017). Characterized by its simple tall cuboidal epithelium with a brush border of microvilli, the proximal convoluted tubule is the longest part of the renal tubule. This brush border of microvilli increases the surface area on the apical side of the epithelial cells for reabsorption.
The proximal convoluted tubule can be further divided into two functional segments, S1 and the proximal part of S2. The distal portion of S2 and S3 are located in the proximal straight tubule.
Anatomical Relations
The proximal convoluted tubules are primarily found in the renal cortex. Each proximal convoluted tubule lies between the glomerular capsule and the proximal straight tubule of the nephron.
Function
A large proportion of reabsorption occurs in the proximal convoluted tubule, whereby fluid and solutes are removed from the filtrate in the tubule and moved back to the bloodstream.
The early part of the proximal convoluted tubule (S1) is responsible for the reabsorption of glucose, amino acids, phosphate, bicarbonate, and various filtered low molecular weight proteins. The later part of the proximal convoluted tubule (S2) is responsible for the reabsorption of urate and citrate (Walsh and Unwin, 2012).
Solutes in the proximal tubule are absorbed by active transport and by facilitated diffusion. Active transport is mediated by the Na+K+-ATPase “sodium pump” on the basolateral side of the proximal tubular cells (Pocock, Richards and Richards, 2013).
List of Clinical Correlates
—Fanconi syndrome
—Proximal renal tubular acidosis
—Lowe syndrome/Dent-2 disease
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
Martini, F. H., Nath, J. L. & Bartholomew, E. F. (2017) Fundamentals of Anatomy & PhysiologyPearson Education.
Pocock, G., Richards, C. D. & Richards, D. A. (2013) Human Physiology, 4 edition. OUP Oxford.
Walsh, S. B. & Unwin, R. J. (2012) Renal tubular disorders. Clin Med (Lond), 12(5), 476-9.
