water & electrolyte balans
DESCRIPTION
anTRANSCRIPT
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Water & Electrolyte BalanceWater is essential to life50% or more of bodyweight, age & sex differencesnewborn to 70 years: 73% to 45% wateryoung adult male: 60%young adult female: 50%key is muscle to fat ratio; total muscle mass
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need to regulate fluid balance inside cells & outsideblood pressureblood volumeelectrolyte balance
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Body fluidsWater40 liters; 60% of body weight
Soluteselectrolytes: ionic compoundssalts: NaCl, NaHCO3acids, bases: H2CO3some proteins: most negatively charged
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Nonelectrolytesusually covalentno electrical chargeorganicglucoselipidscreatinineurea
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Fluids fill 2 compartmentsIntracellularwithin cells25/40 liters or 63%Extracellular15 liters or 46%two partsplasma: 3 litersinterstitial fluid: 12 literswater moves between compartments by osmosis
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Fluid composition differs between compartmentsDue primarily to membrane activityNa / K balance
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Fluid is lost continuallyObligate losseslungsskinG.I. Tractminimal urine flow (500 ml/day)Facultativeexcess urine production
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Balance of gain and lossapproximately 2,500 ml / dayIntake:drinking - 1500 ml, 60%eating - 750 ml, 30%metabolism (water of oxidation) - 250 ml, 10%Loss:lungs & skin - insensible - 700 ml, 28%perspiration - 200 ml, 8%feces - 100 ml, 4%kidneys - 1500 ml, 60%
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Primary mechanism for water replacement is thirst reflexDecrease ECF volumeIncrease concentration of ECFHypothalamicthirst centerDecrease salivaDry mouththirstdrinkRaise volumelower concentration
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Regulating water loss / electrolytesObligate losses cannot be controlledSolute concentrations & urine production are mechanisms for regulating facultative lossNa+ is principal electrolyte90-95% of all soluted in ECFSodium & water regulation tightly linked
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Sodium BalanceNo specific receptorsregulated throughblood volumeblood pressureAldosterone is primary regulatorsodium uptakerelease triggered mostly by AngiotensinII
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Renin from JG cellsSympathetic n.s.low solutesless stretch (low pressure)angiotensin IIvasoconstrictstimulate aldosterone release
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Effect of aldosterone depends on ADH levelsHypothalamushigh sodiumrelease ADH
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ANP also affects water balanceStretch atria (high BP)Collecting ductsJG apparatusposteriorpituitaryadrenalcortexvasodilatekidney tubules Na+ & water reabsorption
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Other factors that affect water balanceestrogensaldosterone-like: enhance Na+ uptakeglucocorticoidsenhance tubular reabsorption of Na+especially at high concentrationsenhance glomerular filtration
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Calcium regulationPTH: from parathyroidactivate osteoclastsenhance intestinal absorptionincrease kidney reabsorption
most calcium in bones as calcium phosphatePO4- reabsorbed in proximal tubulesregulated by PTH
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pH (acid-base) balancebuffering systems in blood & tissuesbicarbonate
phosphate
protein
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Why do we need buffering capacity?Metabolism produces wastesCO2aerobic & anaerobic respirationlactic acidanaerobic respiration of glucosephosphoric acidprotein metabolismketone bodiesfat metabolism
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pH changes that followalter enzymeschange metabolism
* Blood & tissues never really acidic; only relatively more or less so
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Different buffering systems operate in different fluidsPLASMA
proteinsHCO3-EXTRA-CELLULAR FLUID
HCO3-INTRA-CELLULARFLUID
proteinsHCO3-HPO4---
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How is pH regulated?RespiratoryCO2 effects on breathing rate & depthmedullary centershigh capacity0 - 15 fold change in ventilation2 fold change moves pH from 7.2 to 7.6beyond normal limits
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RenalHCO3-by regulating H+ secretion: CO2 H+ secretedPCT, collecting ductfrom CO2 , H20 reaction in filtratecarbonic anhydrase in PCT
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HPO4-protects against dangerous pH in filtrate binds excess H+