TUBULAR SECRETION ::
Further the substances which are not found in the filtrate are also found in the urine These are directly excreted from the blood by the tubules themselves through the enzyme mechanism This is called tubular secretion Tubular cells also manufacture certain new substances This is an active process in which substances like potassium hydrogen creatinine and drugs like phenol penicillin para-amino hippuric acid diodone etc are directly excreted by the tubular cells from the blood
Synthesis of New Substances :: New substances are all manufactured in the tubular cells Ammonia is synthesised by the process of deamination Hippuric acid is synthesised by the combination of glycine with benzoic acid Phosphates are converted from the organic form into inorganic phosphates by phosphatase enzyme system
Counter-current multiplier system ::
The descending limb of the Loop of Henle is relatively permeable to Na+ and cl- whereas in ascending limb active transport of Cl- takes place form the filtrate of tubule to the interstitial fluid of medulla Transport of Cl- is followed passively by Na+ Thus as the fluid moves downwards in the descending limb of loop of henle there is an increase in Na+ and Cl- in the tubule in ascending limb of the loop of henle there is active transport of cl- and hence outward movement of Na+ This causes a fall in
concentration of NaCl as the fluid moves upwards in otherwords there are two parallel streams of liquid flowing opposite to each other (counter current ) resulting in an increased NaCl concentration (multiplier) in the medullary interstitial fluid This is known as counter -current multiplier system
0 Comments