Fluids and Electrolytes

Fluids and ElectrolytesFluids and Electrolytes

Water constitutes 50% to 70% of the total body weight or about 40 Water constitutes 50% to 70% of the total body weight or about 40 litersliters

In males the ratio is ~ 65%In males the ratio is ~ 65%

In females the ratio is less as they have more adipose tissue with In females the ratio is less as they have more adipose tissue with lowerlower

water contentwater content

Body water is distributed between two major compartmentsBody water is distributed between two major compartments

Intracellular (ICF) that makes 40% of total body waterIntracellular (ICF) that makes 40% of total body water

Extracellular (ECF) making 60% of total body water , divided Extracellular (ECF) making 60% of total body water , divided betweenbetween

Interstitial fluid (IF) (80% of ECF) that bathes the tissue cellsInterstitial fluid (IF) (80% of ECF) that bathes the tissue cells

Plasma (20% of ECF) that circulatesPlasma (20% of ECF) that circulates

The difference between IF and plasma is largely the high plasmaThe difference between IF and plasma is largely the high plasma

protein contentprotein content

Marieb Human Anatomy and Physiology seventh edition Pearson Benjamin Cummings

Total body water and its distribution between different compartments

Saladin’s Anatomy & Physiology fourth edition McGraw Hill

Shift of body fluids through different compartments


Water intake and output


Hydration and dehydration


Body water acts as a solvent for two types of particlesBody water acts as a solvent for two types of particles

Electrolytes: particles that can dissociate in solution from other Electrolytes: particles that can dissociate in solution from other partciles partciles

and exist as electrically charged ions or compoundsand exist as electrically charged ions or compounds

Examples: NaExamples: Na++, K, K++, HCO, HCO33--,,

Nonelectrolytes: particles that do not dissociate in solution, they Nonelectrolytes: particles that do not dissociate in solution, they areare

mostly organic mostly organic

Examples: glucose, urea, amino acids, lipidsExamples: glucose, urea, amino acids, lipids


Definitions*Definitions*

Units of measuring solute concentrationUnits of measuring solute concentration Mole = 6 x 10Mole = 6 x 1066 molecules of a substance. This is a constant figure molecules of a substance. This is a constant figure Millimole = 1 / 1000 = 1 / 10Millimole = 1 / 1000 = 1 / 10-3-3 of a mole of a mole Equivalent = amount of ionized solute = moles x valence of soluteEquivalent = amount of ionized solute = moles x valence of solute Example: 1 mmol/L of CaClExample: 1 mmol/L of CaCl22 concentration dissociates into 2 Cl concentration dissociates into 2 Cl--

and one Caand one Ca++++ therefore the Ca therefore the Ca++++ concentration is concentration is 1 mmol x 2 (Ca1 mmol x 2 (Ca++++ valency) = 2 meq/ L valency) = 2 meq/ L Osmole: one osmole = number of particles in a solution in which a Osmole: one osmole = number of particles in a solution in which a

solute solute dissociates dissociates Osmolarity = concentration of particles in solution expressed as Osmolarity = concentration of particles in solution expressed as

osmolesosmoles Electrolyte as well as nonelectrolyte particles contribute to theElectrolyte as well as nonelectrolyte particles contribute to the osmolarity of a solutionosmolarity of a solution * Modified from Costanzo Physiology second edition Saunders


Acid and Base Acid and Base

An acid is a chemical compound that releases H in a solutionAn acid is a chemical compound that releases H in a solution

The more the HThe more the H++ released the stronger the acid and the lower released the stronger the acid and the lower the pHthe pH

An example of a strong acid is HClAn example of a strong acid is HCl

An example of a weak acid is HAn example of a weak acid is H22 CO CO33

A base is a compound that accepts HA base is a compound that accepts H++

An example of a strong base is NaOHAn example of a strong base is NaOH

An examople of a weak base is HCOAn examople of a weak base is HCO33--


pHpH

pH is a measure of HpH is a measure of H++ concentration in body fluids concentration in body fluids

It is expressed in a logarithmic term because of it is a very small It is expressed in a logarithmic term because of it is a very small numbernumber

pH is the negative of HpH is the negative of H++ tenth logarithm tenth logarithm

pH = - logpH = - log1010 (H (H++))


Compartment Volume ShiftsCompartment Volume Shifts

Normally there is a free interchange of water between the different Normally there is a free interchange of water between the different compartments e.g. exchange between intravascular and interstitial compartments e.g. exchange between intravascular and interstitial compartments at the capillary levelcompartments at the capillary level

Loss of blood results in a shift of water from the interstitial to the vascularLoss of blood results in a shift of water from the interstitial to the vascular

compartmentscompartments

Excessive loss of interstitial fluid results in its shrinkage and a shift of Excessive loss of interstitial fluid results in its shrinkage and a shift of intracellular fluid to interstitial compartmentintracellular fluid to interstitial compartment

Burns, hemorrhage, vomiting, diarrhea, excessive sweating, lack of Burns, hemorrhage, vomiting, diarrhea, excessive sweating, lack of water water

intake are all examples intake are all examples

Excessive hydration of ECF leads to water shift into the cellsExcessive hydration of ECF leads to water shift into the cells


Water BalanceWater Balance

To a large extent, the amount of body water is constantTo a large extent, the amount of body water is constant

This is achieved my balancing water intake and loss from the bodyThis is achieved my balancing water intake and loss from the body

About 2500 ml of water is taken (or produced) and the same About 2500 ml of water is taken (or produced) and the same amountamount

is lostis lost

Intake: Drinking (60%)Intake: Drinking (60%)

Water in solid food (30%)Water in solid food (30%)

Internally produced water (10%)Internally produced water (10%)

Output: Urine (60%)Output: Urine (60%)

Loss through the lungs and skin (insensible loss) (30%)Loss through the lungs and skin (insensible loss) (30%)

Sweating (7%)Sweating (7%)

Feces (3%)Feces (3%)


Composition of ICF and ECFComposition of ICF and ECF

NaNa++ and Cl and Cl--, and HCO, and HCO-- make the bulk of ECF ions make the bulk of ECF ions KK++ and Mg and Mg++++ are the main intracellular ions balanced by proteins are the main intracellular ions balanced by proteins

and organic phosphatesand organic phosphates

CaCa++++ is overwhelmingly in the ECF is overwhelmingly in the ECF

The IC pH is ~ 7.1, while the EC is ~7.4The IC pH is ~ 7.1, while the EC is ~7.4

The osmolarity of EC and IC is the same (290 mosm/L) since water The osmolarity of EC and IC is the same (290 mosm/L) since water moves freely across the cell membranemoves freely across the cell membrane

Plasma proteins do not pass into ECF because of their large sizePlasma proteins do not pass into ECF because of their large size

Vander Physiology eighth edition McGraw Hill

Composition of extracellular and intracellular fluids, notice that

the osmolarity is more or less the same


ElectroneutralityElectroneutrality

Each body fluid Each body fluid compartmentcompartment must have an equal number of must have an equal number of anionsanions

and cationsand cations

That is the same concentration in meq/L of the positively charged That is the same concentration in meq/L of the positively charged as as

the negatively charged moleculesthe negatively charged molecules

The plasma membrane has a negative intracellular and The plasma membrane has a negative intracellular and

a positive extracellular surfacea positive extracellular surface


Creation of Concentration DifferencesCreation of Concentration Differences

Across Cell MembraneAcross Cell Membrane

Maintaining a different concentration of the same ion across the Maintaining a different concentration of the same ion across the cell membrane is crucial to cell functioncell membrane is crucial to cell function

Without this difference neural transmission, muscle contraction, Without this difference neural transmission, muscle contraction, and absorption of nutrient from the GI tract and renal tubular and absorption of nutrient from the GI tract and renal tubular function become impossiblefunction become impossible

The sodium potassium pump activated by ATP

It is responsible for the difference between the intracellular and extracellular

concentrations of the two ions

Vander Physiology tenth edition McGraw Hill


Ion Channels and Mediated TransportersIon Channels and Mediated Transporters

Both are membrane integral proteinsBoth are membrane integral proteinsBoth are specific allowing one ion or a specific class of particles Both are specific allowing one ion or a specific class of particles

throughthroughIon channels are permanently open to the specific ionsIon channels are permanently open to the specific ionsMediated transporters undergo conformational changes on eitherMediated transporters undergo conformational changes on either side of the membrane, opening on one side and closing on the side of the membrane, opening on one side and closing on the

otherother then reversing this movement to allow then reversing this movement to allow larger moleculeslarger molecules to pass to passThe result is that ion channels are faster than mediated transportersThe result is that ion channels are faster than mediated transportersMediated transport is of two typesMediated transport is of two types Facilitated diffusionFacilitated diffusion Active transportActive transport


Types of transport across cell membrane

Facilitated diffusion uses a transporter to move particles from higher to lower concentration. It stops when the concentration is equal on both sides of the membrane

Active transport occurs against electrochemical gradient and consumes energy (ATP)

Active transport is of two types: primary and secondary


Ions need open channels to diffuse

They can not diffuse through the bilayerd cell membrane

They move ions several hundred times faster than transporters


Creation of Concentration DifferencesCreation of Concentration Differences Across Cell MembraneAcross Cell Membrane

The NaThe Na++ – K – K++ pump keeps Na pump keeps Na++ concentration higher and K concentration higher and K++ concentration lower outside the cell than inside itconcentration lower outside the cell than inside it

This is an energy consuming processThis is an energy consuming process Energy is derived from adenosine triphospahte (ATP)Energy is derived from adenosine triphospahte (ATP) The transporter acts as an enzyme that extracts energy fromThe transporter acts as an enzyme that extracts energy from ATP and converts it to ADP, the energy is used to move ATP and converts it to ADP, the energy is used to move

particles particles across a gradientacross a gradient NaNa++ - K - K++ ATPase is responsible for creating the large ATPase is responsible for creating the large

concentration gradient across the cell membraneconcentration gradient across the cell membraneTypically for each 3 NaTypically for each 3 Na++ out 2 K out 2 K++ get in resulting in an electrical get in resulting in an electrical

gradient with ECF positive and ICF negativegradient with ECF positive and ICF negative


Primary active transport

Phosphorilation leads to ↑affinity of transporter to the particle

Random oscillations of the transporter opens it to intracellular and

extracellular sides alternately

The transporter is an ATPase


Creation of Concentration Differences Creation of Concentration Differences Across Cell MembraneAcross Cell Membrane

Calcium has its CaCalcium has its Ca++++ ATPase that keeps extracellular Ca ATPase that keeps extracellular Ca++++ concentration higher than its intracellular concentrationconcentration higher than its intracellular concentration

CaCa++++ ATPase is present in cell wall, organelle membranes and ATPase is present in cell wall, organelle membranes and endoplasmic reticulumendoplasmic reticulum

In addition to the ATP consuming transporters, some molecules In addition to the ATP consuming transporters, some molecules establish concentration gradients utilizing the Naestablish concentration gradients utilizing the Na++ gradient gradient established by established by

NaNa++ – K – K++ ATPase ATPase Amino acids, glucose, CaAmino acids, glucose, Ca++++ and H and H++ are transported this way are transported this way This is referred to as “secondary active transport” This is referred to as “secondary active transport”


Creation of Concentration Differences Creation of Concentration Differences Across Cell MembraneAcross Cell Membrane

Secondary Active Transport*Secondary Active Transport* The secondarily transported solute can move in the same directionThe secondarily transported solute can move in the same direction (into the cell) as the primary (Na(into the cell) as the primary (Na++) ion as with glucose molecules) ion as with glucose molecules In this case the process is identified as “cotransport”In this case the process is identified as “cotransport” If the secondarily transported solute goes in the opposite direction If the secondarily transported solute goes in the opposite direction

as as the primarily transported ion (Nathe primarily transported ion (Na++), that is outside the cell then), that is outside the cell then the process is termed “countertransport”the process is termed “countertransport”

**Notice that the primary transport NaNotice that the primary transport Na++ always moves from ECF to the cell inside always moves from ECF to the cell inside

Secondary active transport – Cotransport

Notice that the ion (Na+ in this case) is moving downhill while the

co-transported solute is moving against a high gradient

If the solute moves in an opposite direction than the Na+ the process is

called countertransport (not shown in this figure)Vander Physiology tenth edition McGraw Hill


Movement of different solutes across cell membrane


Regulation of Water IntakeRegulation of Water Intake

Low water intake will lead to Low water intake will lead to ↑plasma ↑plasma osmolality osmolality

Low blood volume or blood pressure activate angiotensin IILow blood volume or blood pressure activate angiotensin II

Both stimuli stimulate hypothalamic thirst center to secrete ADH Both stimuli stimulate hypothalamic thirst center to secrete ADH

High plasma osmolality leads to High plasma osmolality leads to ↓↓salivary secretion salivary secretion → thirst → water → thirst → water intakeintake

Once wet, the buccal mucosa eliminates the feeling of thirstOnce wet, the buccal mucosa eliminates the feeling of thirst

Stretch receptors in the GI tract act on to inhibit thirst center and avoid Stretch receptors in the GI tract act on to inhibit thirst center and avoid excessive water intake and ↓plasma osmolality*excessive water intake and ↓plasma osmolality*


Water intake by the CellWater intake by the Cell

Water is a polar moleculeWater is a polar molecule

It passes through the cell membrane rapidlyIt passes through the cell membrane rapidly

Aquaporins are cell membrane proteins that facilitate the passing Aquaporins are cell membrane proteins that facilitate the passing of waterof water

into the cellinto the cell

The permeability of the cell membrane to water depends on the The permeability of the cell membrane to water depends on the numbernumber

of aquaporinsof aquaporins

The number of aquaporins differ from cell type to the other and in The number of aquaporins differ from cell type to the other and in the same cell in response to different cignalsthe same cell in response to different cignals


Water OutputWater Output

The kidneys have to excrete metabolic by products dissolved in waterThe kidneys have to excrete metabolic by products dissolved in water This mounts to about 500 cc*This mounts to about 500 cc*Skin and lungs loose about 700 cc/daySkin and lungs loose about 700 cc/dayWater is lost with the stoolsWater is lost with the stoolsThe above represent obligatory water loss that needs to be replacedThe above represent obligatory water loss that needs to be replacedThe amount lost in the urine and sweat depend on the amount of The amount lost in the urine and sweat depend on the amount of water ingested in drinks and food and the amount of sweat secretedwater ingested in drinks and food and the amount of sweat secretedADH resorbs water from renal collecting ducts only if the blood volume isADH resorbs water from renal collecting ducts only if the blood volume is lowlowADH secretion is controlled by hypothalamic osmoreceptors and byADH secretion is controlled by hypothalamic osmoreceptors and by significantsignificant changes in blood pressure changes in blood pressure


SodiumSodium

Sodium is the very valuable ion, it maintains total body water and Sodium is the very valuable ion, it maintains total body water and blood volumeblood volume

Sodium is important in maintaining the resting cell membrane Sodium is important in maintaining the resting cell membrane potentialpotential

Sodium gradiants across cell membrane provides the energy for Sodium gradiants across cell membrane provides the energy for cotransportcotransport

of glucose, amino acids, potassium and calciumof glucose, amino acids, potassium and calcium

Sodium bicarbonate is a major ECF bufferSodium bicarbonate is a major ECF buffer

Sodium/potassium pump is important in generating body heatSodium/potassium pump is important in generating body heat

The adult needs 0.5 Gm of sodium/dayThe adult needs 0.5 Gm of sodium/day


Sodium RegulationSodium Regulation

The adult needs 0.5 Gm of sodium/dayThe adult needs 0.5 Gm of sodium/day

Sixty five percent of filtered Na is resorbed by renal PCTSixty five percent of filtered Na is resorbed by renal PCT

Another 25% is resorbed by HLAnother 25% is resorbed by HL

High aldosterone levels resorb the rest in the DCT and CD, otherwiseHigh aldosterone levels resorb the rest in the DCT and CD, otherwise

no Nano Na++ resorption occurs beyond DCT resorption occurs beyond DCT

Water may or may not follow aldosterone NaWater may or may not follow aldosterone Na++ resorbed resorbed

Water resorption depends on ADH aquaporins inserted in CD principal Water resorption depends on ADH aquaporins inserted in CD principal cellscells

Aldosterone is secreted in response to Aldosterone is secreted in response to ↓BP or ↓Na↓BP or ↓Na++ in the JGA perfusate in the JGA perfusate

Baroreceptors respond to ↓BP → vasoconstriction and activation of Baroreceptors respond to ↓BP → vasoconstriction and activation of renin/angiotensin/aldosterone mechanismrenin/angiotensin/aldosterone mechanism


Sodium RegulationSodium Regulation

Atrial Natriuretic Peptide (ANP): produces diuresis reducing blood Atrial Natriuretic Peptide (ANP): produces diuresis reducing blood volumevolume

Promotes NaPromotes Na++ renal CD resorption, inhibits ADH and renin renal CD resorption, inhibits ADH and renin secretionsecretion

and causes vasodilatation and causes vasodilatation


PotassiumPotassium

The most abundant ion in the ICFThe most abundant ion in the ICF

Determines intracellular osmolarityDetermines intracellular osmolarity

Part of the sodium potassium pumpPart of the sodium potassium pump

Essential for protein synthesisEssential for protein synthesis


Potassium RegulationPotassium Regulation

The kidneys main function usually is to excrete potassiumThe kidneys main function usually is to excrete potassiumNormally 60% - 80% of potassium is resorbed through renal PCT Normally 60% - 80% of potassium is resorbed through renal PCT Additional 10% resorbed through HL ascending limbAdditional 10% resorbed through HL ascending limbThe rest is usually lost in the urineThe rest is usually lost in the urineIf interstitial KIf interstitial K++ is low, K is low, K++ will move from cells to interstitial space will move from cells to interstitial space CD principal cells reduce KCD principal cells reduce K++ loss to a minimum loss to a minimumAdrenal cortex cells are sensitive to KAdrenal cortex cells are sensitive to K++ level, an increase will lead level, an increase will lead to aldosterone secretionto aldosterone secretionHigh dietary KHigh dietary K++ intake leads to K intake leads to K++ loss in the urine loss in the urine

The relation between potassium and hydrogen ions in the plasma


Potassium balance in the body

Costanzo Physiology second edition Saunders


CalciumCalcium

Component of the skeletonComponent of the skeleton

Essential for the activation of muscle contraction, including the Essential for the activation of muscle contraction, including the heartheart

Intracellular secondary messenger for hormones and Intracellular secondary messenger for hormones and neurotransmittersneurotransmitters

Part of the coagulation mechanismPart of the coagulation mechanism

Must be kept outside the cells to avoid precipitation with phosphateMust be kept outside the cells to avoid precipitation with phosphate


Phosphorus Phosphorus

Concentrated intracellularly as mon. di and triphosphatesConcentrated intracellularly as mon. di and triphosphates

Part of the nucleic acids, lipophosphates, ATP, GTP and cAMPPart of the nucleic acids, lipophosphates, ATP, GTP and cAMP

Activate many metabolic reactions Activate many metabolic reactions

Help maintain body fluid pHHelp maintain body fluid pH


Acid-Base BalanceAcid-Base Balance

Cell function is possible only in a very tight range of HCell function is possible only in a very tight range of H++ concentration (pH)concentration (pH)

HH++ changes the shape of proteins including the enzymes changes the shape of proteins including the enzymes

The body produces two types of acidThe body produces two types of acid

Fixed: SOFixed: SO44, PO, PO44 , lactic acid, fatty acids, ketone bodies, etc. , lactic acid, fatty acids, ketone bodies, etc.

Volatile: HVolatile: H2COCO33

Normal arterial pH is 7.40, venous pH is 7.35, ICF 7.00Normal arterial pH is 7.40, venous pH is 7.35, ICF 7.00

Acidosis is a tendency towards Acidosis is a tendency towards ↓pH↓pH

Acidemia is a drop in pH below 7.35Acidemia is a drop in pH below 7.35

Alkalosis is a tendency towards a ↑pHAlkalosis is a tendency towards a ↑pH

Alkalemia is a rise of pH above 7.45Alkalemia is a rise of pH above 7.45


Hydrogen Ion MetabolismHydrogen Ion Metabolism

HH++ is produced from the metabolism of proteins and other organic molecules is produced from the metabolism of proteins and other organic molecules

Cell metabolism results in the formation COCell metabolism results in the formation CO22 which reacts with water which reacts with water

COCO22 + H + H22 O= H O= H++ + HCO + HCO33--

The loss of HCO3- in urine and stools constitutes a gain in H+

H+ is lost in vomitus and urine, and is incorporated in organic compounds H+ is also lost in hyperventilation with the excessive loss of CO2

= =



Blood pH is regulated by three mechanismsBlood pH is regulated by three mechanisms

Chemical buffers: act immediatelyChemical buffers: act immediately

Respiratory rate and depth: intermediate speedRespiratory rate and depth: intermediate speed

Renal correction: slow but most potentRenal correction: slow but most potent


Acid-Base BalanceAcid-Base BalanceChemical buffersChemical buffers A buffer is a mixture of a weak acid and its base or a weak base and its A buffer is a mixture of a weak acid and its base or a weak base and its

acid A buffered solution resists change in its pH when a strong acid acid A buffered solution resists change in its pH when a strong acid or a or a

strong base is added to itstrong base is added to it

Chemical buffers can “hide” change in pH Chemical buffers can “hide” change in pH temporarily temporarily until renal until renal control control

takes effecttakes effect

HH22COCO33 / HCO / HCO33-- system system

HCl + NaHCOHCl + NaHCO33 → NaCL + H→ NaCL + H22COCO3 3 (weak acid)

NaOH + HNaOH + H22COCO33 → NaHCO→ NaHCO33 (weak base) + H (weak base) + H22OO

Plasma HCOPlasma HCO33-- levels are referred to as “alkaline reserve” (25 mEq/L) levels are referred to as “alkaline reserve” (25 mEq/L)



Chemical buffersChemical buffersCarbonic acid – Bicarbonate System:Carbonic acid – Bicarbonate System:

HH22COCO33 / HCO / HCO33--

HCl + NaHCOHCl + NaHCO33 → NaCL + H→ NaCL + H22COCO3 3 (weak acid)

NaOH + HNaOH + H22COCO33 → NaHCO→ NaHCO33 (weak base) + H (weak base) + H22OO

Plasma HCOPlasma HCO33-- levels are referred to as “alkaline reserve” (25 levels are referred to as “alkaline reserve” (25

mEq/LmEq/L))


Normally a 20:1 HCO3- to H2 CO3 maintains a plasma pH at the range of

7.35 – 7.45


Acid-Base BalanceAcid-Base BalanceChemical BuffersChemical Buffers

Phosphate system:Phosphate system:

Because of its ICF presence, it is more important as an IC than Because of its ICF presence, it is more important as an IC than plasmaplasma

bufferbuffer

NaNa22HPOHPO4 4 (weak base) and NaHand NaH22POPO44 (weak acid) (weak acid)

HCL + NaHCL + Na22HPOHPO44 → NaCl + NaH→ NaCl + NaH22POPO44

NaOH + NaH2PO4 → Na2HPO4 + H2O



Chemical BuffersChemical Buffers Ammonia/Ammonium System:Ammonia/Ammonium System:NH3 / NH4

+

NH3 is generated in tubular cells absorbs H+

NH3 reacts with Cl-

NH3 + H+ → NH4+ + Cl- → NH4 Cl


Acid-Base BalanceAcid-Base BalanceChemical BuffersChemical BuffersProtein system: Intracellular proteins can expose NH2 or COOH ends

(amphoteric) In acidic medium absorbing H+ as in R-NH2 + H+ → R-NH3

+

In an alkaline medium releasing H+ as in R-COOH → H+ + R-COO-

Hemoglobin is an excellent intracellular buffer, reduced Hgb binds H+


Acid-Base BalanceAcid-Base BalanceRespiratory RegulationRespiratory Regulation COCO22 + H + H22O O →←→← H H22COCO33 →←→← H H++ + HCO + HCO33

--

CO2 is easily expelled from the lungs

The addition of acid will cause the conversion of H2CO3 to H2O and CO2

which is easily expelled from the lungs by ↑ RR The addition of alkali depresses the respiratory center → ↓ RR → ↑

CO2

→ H2CO3 → ↓pH

Respiratory control has a large reserve capacity It addresses “volatile acid” Can affect change in pH within a very short time (minutes)



Renal RegulationRenal Regulation Addresses “fixed acid”, they actually eliminate HAddresses “fixed acid”, they actually eliminate H++ from the body from the body

Corrects the greatest quantity of excesses in acid or baseCorrects the greatest quantity of excesses in acid or base

Correct imbalance slower than other two systemsCorrect imbalance slower than other two systems

Conserves some chemical buffers (HCOConserves some chemical buffers (HCO33-- ) )

Generates some buffers (HCOGenerates some buffers (HCO33--, NH, NH44

+ + from amino acid glutamine))

Secretes HSecretes H++ in the urine in PCT and CD in the urine in PCT and CD

HH+ + is obtained from dissociation of His obtained from dissociation of H22COCO33 created by CO created by CO22 and H and H22OO

For this, carbonic anhydrase is present in the renal cellsFor this, carbonic anhydrase is present in the renal cells



Renal RegulationRenal Regulation The renal tubules convert COThe renal tubules convert CO22 and H and H22O to HO to H22COCO33

HH22COCO33 dissociates into H dissociates into H++ and HCO and HCO33-- in a reversible reaction in a reversible reaction

The enzyme carbonic anhydrase facilitates the two sides of the The enzyme carbonic anhydrase facilitates the two sides of the reactionreaction

In case of excess HIn case of excess H++ the kidney excretes H the kidney excretes H++ in the urine and COand CO22 is is

sent back to the PCT cell where it is converted to HCOsent back to the PCT cell where it is converted to HCO33-- and and

sent back to the ECF elevating the pHsent back to the ECF elevating the pH

In case of alkalosis HCOIn case of alkalosis HCO33-- is secreted in the urine and more H is secreted in the urine and more H++ is is

reabsorbed into the ECFreabsorbed into the ECF

Marieb Human Anatomy and Physiology seventh edition Pearson Benjamin Cummings

HCO3- reclaim from the filtrate

Bicarb left after Na+ resorption is converted to carbonic acid, carbonic anhydrase (CA) splits carbonic acid to H2O and CO2, H2O is passed in the urine, CO2 enters the cell where it is converted to H2CO3 then HCO3

- . This exits to ECF through secondary active transport with Na+

Buffering of H+ by the kidney


Fluids and Electrolytes

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