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Physiology Series

WATER & SODIUMREGULATION PART 2

onald E. Pakasi

PHYSIOLOGY SERIES

Ronald E. Pakasi, MDPhysical Medicine & Rehabilitation Specialist

Spinal Cord Injury Rehabilitation UnitFatmawati General Hospital, Jakarta Indonesia

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Physiology Series

Role of Angiotensin II andAldosterone in Controlling ECF

Osmolarity & Sodium Concentration

Primary: regulates sodium

reabsorption in renal tubules

sodium intake angiotensin II & aldosterone sodium reabsorption

(inverse mechanism w/

sodium

intake)

ECF sodium concentration?

IMPORTANT ROLE ?

Angiotensin II

Aldosterone

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Physiology Series

Role of Angiotensin II andAldosterone in Controlling ECF

Osmolarity & Sodium Concentration

angiotensin II & aldosterone:

amount of sodium in ECF fluid ECF fluid volume by waterreabsorption (following sodium) Little effect unless extremecondition

Angiotensin II

Aldosterone

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Angiotensin II & AldosteroneDo Not Have Major Effect on

Plasma Sodium Concentration

both sodium & water

reabsorption by the renaltubules

(

ECF fluid volume & sodium

quantity)

ADH-thirst mechanismovershadow the angiotensinII-aldosterone system (under normal condition)

Angiotensin II

Aldosterone

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Salt-Appetite Mechanism forControlling ECF Sodium

Concentration & Volume

Modern civilization: too

much sodium intake (mayup to 100-200 mEq/day).

Basic functional human

needs = 10-20 mEq/day Salt appetite: behavioraldrive in the event sodium

deficiency

Usually occurs when eating

a low-sodium diet

Salt-Appetite

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Physiology Series

Salt-Appetite Mechanism forControlling ECF Sodium

Concentration & Volume

2 primary stimuli:

ECF sodium concentration blood volume / blood pressure(associated w/ circulatoryinsufficiency)

Same major stimuli that elicit thirst Neuronal mechanism: analogue tothirst mechanism

AV3V region in brain

Salt-Appetite

Ph i l S i

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INTEGRATION OF RENALMECHANISM FOR CONTROLOF BLOOD VOLUME AND ECF

VOLUME; AND RENALREGULATION OF

ELECTROLYTES

Integration

Ph i l S i

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Urinary System-Interconnections

Integration

Ph i l S i

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Sodium Excretion is PreciselyMatched to Intake Under Steady-

State Conditions

Excretion by kidney is determined byintake

Sodium excretion is almost preciselythe amount of sodium intake If kidney function disturbances are nottoo severe sodium balance:

Intrarenal

adjustments w/ minimal changes

in ECF fluid volume Other systemic adjustments (BP,hormones, alteration of sympathetic

activities)

Sodium Excretion

Physiology Series

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Control of Sodium Excretion:Intrarenal Changes

Altering glomerular filtration rate Altering tubular sodium reabsorption rates

Sodium Excretion

Physiology Series

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Role of Pressure Natriuresis &Pressure Diuresis in Maintaining

Body Sodium & Fluid Balance

Pressure natriuresis: effect of bloodpressure on sodium Rise of sodium excretion w/ elevatedBP

Pressure diuresis: effect of bloodpressure on water excretion

Increased BP to raise urinary

volume excretion

Pressure Natriuresis

Pressure Diuresis

Physiology Series

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Effect of Arterial Pressure on

Urinary Sodium Output

Rise of BP 30-50 mmHg: urinarysodium output 2-3x

Effect is independent fromsympathetic activity or RAA system Chronic increase of BP:effectiveness of pressure natriuresis

is greatly enhanced Because of the suppression on RAAsystem

Pressure Natriuresis

Pressure Diuresis

Physiology Series

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Physiology Series

Role of Pressure Natriuresis &Pressure Diuresis: Key Components

of a Renal-Body Fluid Feedback

Pressure Natriuresis

Pressure Diuresis

Physiology Series

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Basic Renal Body Fluid

Feedback1. fluid intake (w/ sodium) >urine output temporary fluid accumulation 2. Accumulation in blood & interstitialspaces blood volume & ECF fluid

volume (small variables)

3. mean circulatory filling pressure 4. pressure gradient for venous return 5.

cardiac output

6. arterial pressure 7. urine output (pressure diuresis) 8.

fluid excretion

Physiology Series

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Prevent continuous accumulation ofsalt and water

If kidney function normal: pressurediuresis mechanism is effective Large change in salt & water intakecan be accomodated with only slightchanges in blood volume, ECF fluid

volume, CO & arterial pressure Opposite sequence occurs whenfluid intake falls below normal

Role of Pressure Natriuresis &Pressure Diuresis: Key Components

of a Renal-Body Fluid Feedback

Pressure Natriuresis

Pressure Diuresis

Physiology Series

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Precision of Blood Volume andECF Fluid Volume Regulation

Blood volume remains almostexactly constant despiteextreme changes in daily fluidintake

1. Slight change in BV cause amarked change in CO2.

Slight change in CO cause alarge change in BP

3. Slight change in BP cause alarge change in urine output

Physiology Series

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y gy

To be continued

Ronald E.Ronald E. PakasiPakasi, MD, MDPhysical Medicine & Rehabilitation Specialist

Spinal Cord Injury Rehabilitation Unit

Fatmawati General Hospital

Jakarta, Indonesia