Na/glucose symporterLuminalNo-facilitated transporter-Na and glucose-glucose is absorbedNa/H exchangerLuminalYes – angiotensin II-Hormone changes speed-kicks out HNa/K ATPaseBasolateralYes – angiotensin II-sodium is not favorable-requires ATPWater channel (AQ I)LuminalNo-Water wants to go into the capillariesWater channel (AQ I)BasolateralNo-same as aboveAmino acid uniporterBasolateralNo-down concentration gradientGlucose uniporterBasolateralNo-Down concentration gradientParacellular H2O, K, ClNANo-reabsorptionDiabetes Mellitus (WILL BE A QUESTION)oSymptoms: glucose in the urine (glucosoria), increased urine volume oThe nephron is incapable of reabsorbing all the glucose that it normally was able to – saturation of thesodium/glucose symporteroIncreased level of glucose filling into Bowman’s space compared to healthy individualsoCaused by the deficiency of insulin production (type I) or a decreased cellular response to insulin (typeII)More glucose will be filtered into Bowman’s capsule in individualswith diabetes mellitus than in an individual with normal levels ofglucose in their bloodoWhy would there be more glucose filtering into Bowman’s capsule?Increased [glucose]PLASMAPancreas stops making insulin – body doesn’t respond to itFiltered load of glucose = GFR x [glucose]PLASMAFiltered load of glucose will increaseoHow does decreasing glucose reabsorption affect water reabsorption?Presence of glucose remaining in the filtrate increases the osmotic pressure of the filtrate, preventing water from being reabsorbed by osmosisDescending loop of Henle – reabsorbs wateroMust have aquaporins (reabsorbs only water)oNo paracellular transportoNo hormonal controlAscending loop of Henle – reabsorbs ionsoNo water reabsorption – no aquaporinsoParacellular transportoNo hormones to change channelsDistal convoluted tubule – reabsorbs ionsoImpermeable to wateroNo paracellular transportoReabsorbs the same ions as the ascending loop of Henle but also absorbs CaoCa absorption is usually hormonally regulated (Parathyroid hormone)Differences between distal convoluted tubule and ascending limboDistal has no paracellular reabsorption – AL doesoDistal reabsorbs Ca and is hormonally regulatedoBoth absorb ions and don’t absorb water8
Collecting Duct – fine tuning of the filtrateConcentration of the filtrate - 300mOsmoStep 1 – proximal tubule/descending limbEqual ions and water reabsorbedoStep 2 – 600 – 1200mOsm (depending on location)Water reabsorbedWater leaves into interstitial space until we reach equilibrium1200mOsm at baseoStep 3 Ions reabsorbedFiltrate osmolarity decreasesSolute/ions are leavingoStep 4If ADH is present, then water is reabsorbed (moves to equilibrium)Most concentrated urine you can produce is 1200mOsmRegulation of water balanceoIncreased fluid intake generally means increased urine output (and vice versa) oWater balance controlled independently of salt balance in humans oUrine volume can be as low as 0.4 L/day, as high as 25 L/day (avg. is 1.5 L/day) oMost fluid intake comes from beverages and food oMost fluid is lost through urine excretionWater levels and blood pressure oKidneys can control blood pressure through adjusting the blood volume oIf total body water decreases, the extracellular fluid volume is decreased and this causes a decrease inblood pressureoBlood pressure – triggers ADHAnti-diuretic hormone (ADH) – aka vasopressinoMade by: neuroendocrine cells in the hypothalamus oStored: posterior pituitary oPeptide hormone - released into the blood when triggered by the stimulus oStimulus: high plasma osmolarity, low ECF volume9Channel/transporterLocationRegulatedNotesWater channel (AQII)LuminalYes – ADHOnly occurs if 1 is presentWater channel (AQII & IV)BasolateralNoNa ChannelLuminalYes – aldosteroneK ChannelLuminalYes – aldosteroneSecreting it into the filtrateNa/K ATPaseBasolateralYes - aldosteroneAgainst gradient
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- Fall '12
- Physiology, Nephron, glomerular capillaries