A. Functions of Proximal Convoluted Tubule (PCT)
$1.$ PCT absorbs almost all essential nutrients.
$2.$ PCT absorbs about 70-80 % electrolytes and water.
$3.$ As PCT selectively secretes H+ ions, ammonia and potassium ions into the filtrate and also absorbs ${\mathrm{H}\mathrm{C}\mathrm{O}}_3^{-}$
from it, it maintains the pH and ionic balance of the body fluids.
B. Functions of Henle's Loop
$1.$ Maintenance of high osmolarity of medullary interstitial fluid.
$2.$ Reabsorption to some extent (some water and electrolytes enter medullary fluid).
C. Functions of Distal Convoluted Tubule (DCT)
$1.$ Conditional reabsorption of ${\mathrm{N}\mathrm{a}}^{+}$ and water.
$2.$ Reabsorption of ${\mathrm{H}\mathrm{C}\mathrm{O}}_3^{-}$ and selective secretion of ${\mathrm{H}}^{+},\mathrm{ }{\mathrm{K}}^{+,}$ and ${\mathrm{N}\mathrm{H}}_3$ for maintaining the pH and sodium-potassium balance in the blood.
D. Functions of Collecting Duct
$1.$ Reabsorbed of large amounts of water resulting in the production of concentrated urine.
$2.$ Small amounts of urea enter the medullary interstitium to keep up the osmolarity.
$3.$ By the selective secretion of ${\mathrm{H}}^{+}$ and ${\mathrm{K}}^{+}$ ions, collecting ducts also plays an important role in the maintenance of pH and ionic balance of the blood.