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

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capsule. Bowman's capsule acts to "filter" or separate some of thesubstances that are located in blood plasma from others. This is becausesome substances are small enough to fit through the pores of the membraneof Bowman's capsule and some are too large and thus do not enterBowman's capsule with the rest of the blood plasma. Water, salt ions(sodium, potassium and choride), glucose molecules, amino acids and ureamolecules are all small enough to go through the membrane pores intoBowman's capsule. Blood cells (rbc, wbc and platelets) and proteins on theother hand are too large to leave the capillaries or enter Bowman's capsule.The fluid inside of Bowman's capsule gets a name change; it is now called"filtrate" because it is blood plasma that has been filtered, This filtrate isidentical to blood plasma minus the blood cells and proteins. Filtrate is saidto be isotonic to blood plasma with respect to its concentration of water, saltions, glucose, amino acids and urea. The filtrate will then proceed fromBowman's capsule through the rest of the nephron in the following order:proximal convoluted tubule, loop of henle, distal convoluted tubule andfinally the collecting tubule. From the collecting tubule, the filtrate will enterthe pelvis of the kidney and be called urine.2. ReabsorptionUseful materials such as sugars and salt ions are reabsorbed back into theblood stream. That is, materials that could still be used by the body are sentback to the blood. Reabsorption happens as filtrate passes sequentiallythrough the nephron. Materials re-entering the blood stream do so throughthe capillary network surrounding the nephrons. In short, "good" stuff is sentfrom the nephron back into the blood.A. Proximal Convoluted Tubule (PCn:As the filtrate enters the PCT approximately 80% of the salt ions (sodiumand potassium), glucose and amino acids are ACTIVELYTRANSPORTED out of the PCT and back into the blood stream byspecial "pumping" cells located in the walls of the PCT. The process ofactive transport requires energy. Energy in the form of ATP is suppliedby the numerous mitochondria that are embedded in the walls of thePCT. Because of ionic attraction, negatively charged chloride ions (CI-)will flow passively out of the PCT as they are attracted by the positivelycharged sodium and potassium ions (Na+, K+). As the concentration ofthe above mentioned solute molecules drops inside of the PCT, water
then diffuses out of the PCT and into the capillary network passively bythe process of OSMOSIS. The lining of the PCT contains microvilli toincrease the surface area over which this reabsorption can occur.B. Descending Loop of Henle:As the filtrate travels into the descending Loop of Henle, both sodiumand potassium ions passively diffuse from the salty tissues of thesurrounding medulla BACK INTO the Loop of Henle. (Although this isreabsorption of materials, the materials are not going back into the bloodstream at this point). At the same time, water continues to move out ofthe Loop of Henle and into the capillary network by osmosis. The filtrateat this point is more concentrated (hypertonic) with respect to salt ionsthan it was in the PCT, both because water has been removed from it, andbecause salt ions have been again added to it.C. AscendineLoop of HenleAs the filtrate proceeds up into the ascending Loop of Henle, the chorideions are actively pumped back out of the nephron. Because of ionicattraction, sodium ions then passively follow the chloride ions out of thetubule and into the tissues of the medulla. These ions only move into themedulla and not back into the blood stream. Since the ascending Loop ofHenle is impermeable to water, water cannot leave this part of thenephron. Because of this, the filtrate gets more dilute again.Because the opposite happens in the ascending and descending Loops ofHenle, the process is called the COUNTER CURRENTMECHANISM. The process is also known as the CHLORIDE SfUFT.D. Distal Convoluted Tubule (DCT)As the filtrate passes through this part of the nephron, water continues topassively diffuse out of the nephron and back into the blood. Watercontinues to diffuse out of the DCT because the surrounding tissues ofthe medulla are now very salty due to so much sodium and chloride ionsaccumulating there. The salty tissues attract the water out of the DCTbecause the medulla is hypertonic with respect to salt concentration whencompared with the salt concentration of the filtrate (now hypotonic).Water that enters the medulla will then diffuse back into the blood
Page 1: The Roles of the Nephronof the 120
Page 5 and 6: The Counter Current Mechanism of th
Page 7 and 8: FU",t.Ic r1
Page 9 and 10: Use your notes to complete the foll
Page 11 and 12: How are PLASMA and FILTRATE alike?.

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

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