The Roles of the Nephron of the 120 ml of blood that is ... - Mrs Stovel

The Counter Current Mechanism of theNephronThe loop of Henle works toward thegoal of water conservation. Animals that livein a terrestrial environment need to be carefulnot to waste water. It is clearly a waste,if wateris in short supply, to release too much waterwith the urine. As a result there needs to be amechanism to encourage water out of the urineand back into the blood. The loop of Henlecreates that mechanism in terrestrialanimals.There is no way of actively capturingwater in the urine that is passing through thecollecting ducts. It would almost seem too lateto capture the water that is already on its wayout of the body. However, the nifty nephroncreates a trick with its loop of lienle to get thewater out of the collecting duct before it leavesthe kidney, It does so by creating a saltyenvironment in the medulla area of thekidney.The ascending loop of Henle activelytransports chlorine ions out of the filtrate withcarrier proteins. Chlorine builds up in thefluids of the medulla by active transport.Because it is a negative ion, it creates a causefor the sodium ion, which is positive, to rush outof the loop after chlorine. The sodium rushesout by diffusion because of its 'fatal attraction'to chlorine. The chlorine and the sodium ionscollect and dominate the fluids outside the loopof I-fenle creating a salty environment. Thissalty environment catches the attention of thewater that is passing through the nearbycollecting duct. The collecting duct ispermeable to water but not permeable to thesalt. Water can. not resist moving into thesalty medulla. The salt creates an osmoticpressure that pulls the water out of the collectingduct by osmosis. (Water has a 'fatal attraction'to salty solutions.) Once the water is out of theduct it is no longer destined for elimination butcan' now be picked up by the nearby. ,Moodcapillaries and returned to be used by;.bodysystems.Meanwhile, back at the loop of`-•Henle,trouble is starting. The ascending loop isrunning out of salt. There is no need to worry.The salt trick can continue because thedescending loop in its wisdom is stealing backthe salt that the ascending loop is so generouslyreleasing. This helps to keep a constant flow ofsalt inside the loop for the ascending lope topump out . Because of the generosity gftheascending loop and the stinginess of thedescending loop a salt trade or salt current isestablished as the salt moves ouc of theascen ding loop and into the descending loop,This salt current established by the loop oflienle maintains an environment that attractswater out of the ducts containing urine andback into the blood. This process is called thecounter current mechanism.