Question

Describe the process of urine urine formation in kidney

Answer 1

Answer:

the kidney contain the extra water present in the body and release in the urine tube

Answer 2

Urine Formation: Three main processes are involved in urine formation:

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.

Tubular Secretion:  

 Transport of substances across tubular epithelium from blood to filtrate is called secretion.

 Tubular secretion helps in the maintenance of ionic and acid-base balance of body fluids.

 PCT maintains pH and ionic balance of body fluid by selective secretion of H+, K+ and NH3 into filtrate.

 DCT and collecting duct also maintain pH and ionic balance by secreting H+ and K+.

Note: PCT and DCT are the main sites of tubular secretion.

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