Absorptive capabilities of different tubular segments
Proximal tubule
65 % of the reabsorption and secretion take place. Only 35% of the GF leaves the proximal tubule.
Thin segment of Loop of Henle
Permeability of the epithetical cells of descending limb of Loop of Henle is great and occurs by simple diffusion. It is highly permeable to water and moderately permeable to urea and Na2+.
Ascending limb of Loop of Henle
Ascending limb of Loop of Henle is less permeable to water and more permeable to urea. Thick segment of Loop of Henle and distal tubule
They have rudimentary brush border and cells adapted for Na2+ transport against concentration gradient. They are impermeable to water and urea. Here, active absorption of Na2+ and active secretion of K+ is controlled by aldosterone.
Collecting tubule
Final concentration of urine takes place in the collecting tubule. It has two functional units, cortical and medullary portion. Cortical portion is impermeable to urea and medullary portion is moderately permeable to urea. Permeability of collecting tubule to water is determined by the concentration of Antidiuretic hormone (ADH) in the blood. Large amount of ADH causes collecting tubule to be highly permeable to water. In the absence of ADH, very little water is reabsorbed. They can secrete H+ into the tubule.