Renal tubules are long, cylindrical patchy tubules that extend from the base of Bowman’s capsule to the ends of the collecting ducts. Each renal tubule is approximately 3 cm in length and has an average diameter of 60 micrometers. It consists of three parts. These are-
(i) Proximal convoluted tubule: The tubule associated with Bowman’s capsule is called proximal convoluted tubule. Its length is about 14 cm and diameter is 57-60μ. These peritubules are covered by epithelial cells with capillaries or brush borders. At one end of the cells are numerous microscopic finger-like projections or microvilli. It is located in the cortex. This duct carries the filtrate from the glomerulus to the loop of Henley. The proximal tubule reabsorbs water, sodium ions, potassium, amino acids, glucose, chloride, peptide creatine and bicarbonate ions from the glomerular filtrate.
(ii) Loop of henle: The U-shaped tube extending from the proximal convoluted tubule to the distal convoluted tubule is called loop of Henle. This is called nephron leakage. It is located in the medulla and cortex. Its length is 11 mm and diameter is 20 μm. It consists of two parts. Descending limb and Ascending limb. The descending arm extends from the end of the proximal tubule to the medulla and the ascending arm is located in the cortex region. It is called loop of Henle after German medical scientist Friedrich Henle.
(iii) Distal convoluted tubule: The part from the loop of Henley to the collecting duct is called distal convoluted tubule. Its length is 5 mm and diameter is 22.5 μ. It is surrounded by peritubule capillary or epithelial cells. It is located in the cortex. The next part of the distal patchy duct is called the collecting duct. Several collecting ducts join to form the Duct of Bellini.