Ronald E. Ronald E. PakasiPakasi, MD, MDPysicalPysical Medicine & Rehabilitation SpecialistMedicine & Rehabilitation Specialist

Jakarta, IndonesiaJakarta, Indonesia

Daily Intake of WaterDaily Intake of Water

Ingested in the form of liquid or foodIngested in the form of liquid or foodApp. 2100 ml/dayApp. 2100 ml/day

Synthesized from carbohydrates oxidationSynthesized from carbohydrates oxidationApp. 200 ml/dayApp. 200 ml/day

Total intake app. 2300 ml/dayTotal intake app. 2300 ml/dayInfluencing factors e.g.: climate, habits, level of physical Influencing factors e.g.: climate, habits, level of physical activityactivity

Daily Loss of Body Water:Daily Loss of Body Water:(1) Insensible Water Loss(1) Insensible Water Loss

Influencing factors: respiration & Influencing factors: respiration & diffusion through skindiffusion through skin

App. 700 ml/day (300App. 700 ml/day (300--400 ml/day 400 ml/day from each of the influencing from each of the influencing factors)factors)

Diffusion through skinDiffusion through skin: : –– INDEPENDENT FROM INDEPENDENT FROM

SWEATING !!SWEATING !!–– Minimized by cholesterolMinimized by cholesterol--filled filled

cornified layer of the skincornified layer of the skin–– Denuded layers: rate of evaporation Denuded layers: rate of evaporation

increase 10increase 10--fold (to 3fold (to 3--5 L/day)5 L/day)

Daily Loss of Body Water:Daily Loss of Body Water:(1) Insensible Water Loss(1) Insensible Water Loss

RespirationRespiration::–– Averages 300Averages 300--400 ml/day 400 ml/day

((see last pagesee last page))–– Air in Air in respresp. tract . tract →→ saturated w/ saturated w/

moisture to a vapor pressure about 47 moisture to a vapor pressure about 47 mm Hgmm Hg

–– Inspired air (pressure <47 mm Hg) Inspired air (pressure <47 mm Hg) →→continual water losscontinual water loss

–– Influencing factor: cold weather Influencing factor: cold weather →→ vapor vapor pressure decrease ~ 0 mm Hg pressure decrease ~ 0 mm Hg →→ ↑↑ water water loss from lung (dry feeling in RT)loss from lung (dry feeling in RT)

Daily Loss of Body Water:Daily Loss of Body Water:(2) Fluid Loss in Sweat(2) Fluid Loss in Sweat

The amount is highly variableThe amount is highly variableInfluencing factors: physical activity & Influencing factors: physical activity & environmental temperatureenvironmental temperatureNormal volume app. 100 ml/dayNormal volume app. 100 ml/dayVery hot weather or heavy exercise: Very hot weather or heavy exercise: up to 1up to 1--2 L/hour2 L/hour

Daily Loss of Body Water:Daily Loss of Body Water:(3) Water Loss in Feces(3) Water Loss in Feces

Small amountSmall amountApp. 100 ml/dayApp. 100 ml/dayIncreased in diarrhea Increased in diarrhea

Daily Loss of Body Water:Daily Loss of Body Water:(4) Water Loss by the Kidney(4) Water Loss by the Kidney

The most important regulation The most important regulation to maintain balance between:to maintain balance between:–– Water intake & outputWater intake & output–– Electrolyte intake & outputElectrolyte intake & output

Urine volume: Urine volume: –– Dehydrated vs. Tremendous Dehydrated vs. Tremendous

drinking: 0.5 L/day vs. 20 L/daydrinking: 0.5 L/day vs. 20 L/day–– Normal: app. 1400 ml/dayNormal: app. 1400 ml/day–– Prolonged heavy exercise: app. Prolonged heavy exercise: app.

500 ml/day500 ml/day

BODY FLUID BODY FLUID COMPARTMENTSCOMPARTMENTS

Extracellular FluidExtracellular FluidBlood PlasmaBlood PlasmaInterstitial FluidInterstitial Fluid

Intracellular FluidIntracellular FluidTranscellularTranscellular fluid fluid (1(1--2L) 2L)

Synovial Synovial PeritonealPeritonealPericardialPericardialIntraocularIntraocularCerebrospinalCerebrospinal

Plasma3.0 L

Interstitial Fluid11.0 L

Intracellular Fluid28.0 L

Cell Membrane

Capillary Membrane

IntakeOutput

Extracellular Fluid (14.0 L)

Body Water RegulationBody Water Regulation

↓ Arterial Pressure

↑ Renal Sympathetic Nerve Activity ↓ Glomerular Capillary Pressure

↑ Renal Arteriolar Vasoconstriction

↑ Renin Release ↓ Glomerular Filtration Rate

↑ Angiotensin II

↑ Aldosterone

↑ Renal Sodium Reabsorption

↑ Renal Fluid Reabsorption ↓ Urine Output Rate

Control of Control of ExtracellularExtracellular Fluid Fluid Osmolarity & Sodium Osmolarity & Sodium ConcentrationConcentration

ECF osmolarity & sodium concentration are ECF osmolarity & sodium concentration are regulated closelyregulated closely

Osmolarity: Osmolarity: ~~ 300 300 mOsmmOsm/L/LSodium : Sodium : ~~ 140 140 –– 145 145 mEqmEq/L/L

Osmolarity: Osmolarity: 94% sodium & related anions (bicarbonate & chloride)94% sodium & related anions (bicarbonate & chloride)33--5% glucose, urea, etc.5% glucose, urea, etc.

Sodium ions & associated anions in ECF Sodium ions & associated anions in ECF →→principal determinants of fluid movement across principal determinants of fluid movement across the cell membranethe cell membrane

Regulation of Sodium & Regulation of Sodium & Osmolarity of ECFOsmolarity of ECF

OsmoreceptorOsmoreceptor--ADH systemADH systemThirst mechanismThirst mechanism

Osmoreceptor Osmoreceptor ––ADH Feedback ADH Feedback SystemSystem

Water Deficit

↑ ExtracellularOsmolarity

↑ ADH Secretion(posterior pituitary)

↑ Plasma ADH

↑H2O permeabilityin distal tubules,collecting ducts

↑ H2O Reabsorption

↓ H2O excreted

Cardiovascular Reflex Cardiovascular Reflex Stimulation of ADHStimulation of ADHCV controlled ADH: in response to CV controlled ADH: in response to ↓↓BP and/or blood volume:BP and/or blood volume:

Arterial Arterial baroreceptorbaroreceptor reflexesreflexesCardiopulmonary reflexesCardiopulmonary reflexes

(Sites: aortic arch, carotid sinus, atria)(Sites: aortic arch, carotid sinus, atria)→→ afferent: afferent: VagusVagus & & GlossopharyngealGlossopharyngealnervesnerves

Other factors:Other factors:Decreased arterial pressureDecreased arterial pressureDecreased blood volumeDecreased blood volume

ROLE OF THIRST IN CONTROLLING ECF ROLE OF THIRST IN CONTROLLING ECF OSMOLARITY & SODIUM CONCENTRATIONOSMOLARITY & SODIUM CONCENTRATION

To minimize fluid loss during water To minimize fluid loss during water deficitsdeficits–– (role of (role of osmoreceptorosmoreceptor--ADH system)ADH system)Thirst mechanism regulates fluid intakeThirst mechanism regulates fluid intakeStimuli for thirst:Stimuli for thirst:–– ↑↑ ECF osmolarity ECF osmolarity –– ↓↓ blood volumeblood volume–– ↓↓ blood pressureblood pressure–– ↑↑ Angiotensin IIAngiotensin II

Thirst StimuliThirst Stimuli↑↑ ECF osmolarity ECF osmolarity

→→ intracellular dehydration intracellular dehydration →→thirst centre thirst centre →→ thirst sensationthirst sensation

↓↓ ECF volume & arterial volumeECF volume & arterial volumeIndependent stimulusIndependent stimulusStimulate thirst by means of Stimulate thirst by means of ↑↑ plasma osmolarityplasma osmolarity

↓↓ blood volume (e.g. haemorrhage)blood volume (e.g. haemorrhage)Same as above; plasma osmolarity non increased Same as above; plasma osmolarity non increased

↑↑ AngiotensinAngiotensin IIIIStimulated by hypovolemia & low BPStimulated by hypovolemia & low BPEffects on thirst is to restore BP & blood volumeEffects on thirst is to restore BP & blood volume

Threshold for Osmolar StimulusThreshold for Osmolar Stimulus

Water evaporation from lungs, GIT, Water evaporation from lungs, GIT, sweating, & kidney sweating, & kidney →→ dehydration dehydration tendency tendency →→ ↑↑ sodium concentrationsodium concentrationIf sodium concentration If sodium concentration ↑↑ app. 2 app. 2 mEqmEq/L /L above normal above normal →→ thirst mech. activatedthirst mech. activated(Osmolar) threshold for drinking(Osmolar) threshold for drinking

Integrated Responses for Integrated Responses for OsmoreceptorOsmoreceptor--ADH & Thirst MechanismADH & Thirst Mechanism

OsmoreceptorOsmoreceptor--ADH & thirst mechanism ADH & thirst mechanism work in parallel work in parallel →→ regulate ECF osmolarity regulate ECF osmolarity & sodium concentration& sodium concentrationAdditional high salt intake Additional high salt intake →→ osmolarity osmolarity feedback systems are able to keep plasma feedback systems are able to keep plasma osmolarity constantosmolarity constant

Effects of Large Changes in Sodium Effects of Large Changes in Sodium Intake on ECF Sodium ConcentrationIntake on ECF Sodium Concentration

136

140

144

148

152

156

0 30 60 90 120 150 180Sodium intake (mEq/day)

Plasma sodiumconcentration(mEq/L)

Normal

ADH & thirstsystemblocked No effect on

plasma sodium concentration

If ADH & thirst mechanism fail If ADH & thirst mechanism fail simultaneously: sodium concentration & simultaneously: sodium concentration & osmolarity are controlledosmolarity are controlledIf sodium intake is increased after blocking If sodium intake is increased after blocking ADHADH--thirst system: relative changes in thirst system: relative changes in plasma sodium concentration occurplasma sodium concentration occurNo other feedback mechanismNo other feedback mechanism

To be continued To be continued ……