Question

describe ultrafiltration and reabsorption in nephron

Answer 1

In renal physiology, ultrafiltration occurs at the barrier between the blood and the filtrate in the glomerular capsule (Bowman's capsule) in the kidneys. ... Further modification of ultrafiltrate, by reabsorption and secretion, transforms it into urine.

Answer 2

i. Glomerular Filtration/Ultrafiltration:

 Filtration of blood occurs through three layers, i.e. endothelium of glomerular blood vessels, epithelium of Bowman's capsule and basement substance between these two layers.

 Epithelial cells of Bowman's capsule called podocytes are arranged in a manner so as to leave some minute spaces called filtration slits or slit pores.

 Blood is filtered so finely through these membranes that almost all the constituents of plasma except proteins pass into the lumen of Bowman's capsule. This process is called ultrafiltration.

 The filtrate that enters the tubules of nephrons is called glomerular filtrate or ultra-filtrate.

Note: Glomerular filtrate contains essentially all constituents of blood except blood cells and plasma proteins.

 The amount of filtrate formed by kidneys per minute is called glomerular filtration rate (GFR).

 GFR in a healthy individual is about 125 ml/minute, i.e. 180 litres per day.

ii. Tubular Reabsorption:

 A comparison of volume of filtrate formed per day (180 litres) with that of the urine released (1.5 litres), suggests that nearly 99% of the filtrate is reabsorbed by the renal tubules. This process is called tubular reabsorption.

 Selective transport of substances across tubular epithelium from ultra-filtrate to blood is called reabsorption.

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