ELECTROLYTES & ELECTROLYTES & ACID-BASE HOMEOSTASISACID-BASE HOMEOSTASIS

(Keseimbangan Asam-Basa dan Elektrolit)(Keseimbangan Asam-Basa dan Elektrolit)

FAKULTAS KEDOKTERAN GIGIUNIVERSITAS ANDALAS

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Electrolyte BalanceElectrolyte Balance• Electrolytes are salts, acids, and bases,

but electrolyte balance usually refers only to salt balance

• Salts are important for:– Neuromuscular excitability– Secretory activity– Membrane permeability– Controlling fluid movements

• Salts enter the body by ingestion and are lost via perspiration, feces, and urine

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Electrolytes – The Ion Components Inside and Electrolytes – The Ion Components Inside and Outside the Cells Are Not the Same.Outside the Cells Are Not the Same.

Electrolyte Symbol Reference range(serum)

Potassium K+ 3.7-5.2 mEq/L

Magnesium Mg2+ 1.8-2.4 mg/dL

Phosphate PO4- 4.5-6.0 mg/dL ( 11 yrs)3.0-4.5 mg/dL ( 12 yrs)

Sodium Na+ 136-145 mEq/L

Chloride Cl- 98-108 mEq/LBicarbonate HCO3- 22-32 mEq/LCalcium Ca2+ 8.9-10.2 mg/L

ICF

ECF

Adapted from Sara Duesterhoeft’s lecture, 2002.

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Sodium in Fluid and Electrolyte Sodium in Fluid and Electrolyte BalanceBalance

• Sodium holds a central position in fluid and electrolyte balance

• Sodium salts:– Account for 90-95% of all solutes in the ECF– Contribute 280 mOsm of the total 300 mOsm

ECF solute concentration• Sodium is the single most abundant cation in

the ECF

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SodiumSodium• Plays major role in maintaining ECF

concentration (osmolality) and volume

• Sodium is the only cation exerting significant osmotic pressure

• Important in generation and transmission of nerve impulses

• Important in acid-base balance

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HypernatremiaHypernatremia• Hypernatremia due to

– Water loss or– Sodium gain

• Hypernatremia results in– Hyperosmolality → water shifts out of cells →

cellular dehydration

• Primary protection against hypernatremia is thirst

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HypernatremiaHypernatremia

• Manifestations include thirst, lethargy, seizures, and coma

• Hypernatremia secondary to water deficiency often due to inability to get fluids

• Also due to deficiency in ADH

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HyponatremiaHyponatremia• Due to:

– loss of Na-containing fluids, or – water excess (dilutional hyponatremia)

• Hyponatremia → hypoosmolality → water moves into cells

• Clinical manifestations include confusion, nausea, vomiting, seizures, and coma

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PotassiumPotassium• Potassium major ICF cation

• Potassium is necessary for– Transmission and conduction of nerve

impulses – Normal cardiac rhythms– Skeletal muscle contraction– Acid-base balance

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PotassiumPotassium

• Critical to action membrane potential

– Sources of potassium • Fruits and vegetables (bananas and

oranges)• Salt substitutes • Potassium medications (PO, IV)• Stored blood

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HyperkalemiaHyperkalemia

• Causes– Increased retention

• Renal failure• Potassium sparing diuretics

– Increased intake– Mobilization from ICF

• Tissue destruction • Acidosis

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HyperkalemiaHyperkalemia

• Clinical Manifestations :– Skeletal muscles weak or paralyzed

– Ventricular fibrillation or cardiac standstill

– Abdominal cramping or diarrhea

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HypokalemiaHypokalemia

• Causes– Increased loss

• Certain diuretics • GI losses• Movement into cells

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HypokalemiaHypokalemiaClinical ManifestationsClinical Manifestations

• Potentially lethal ventricular arrhythmias • Increased digoxin toxicity in those taking

the drug• ECG changes• Skeletal muscle weakness and paralysis • Muscle cell breakdown

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HypokalemiaHypokalemiaClinical ManifestationsClinical Manifestations

• Decreased GI motility

• Altered airway responsiveness

• Impaired regulation of arterial blood flow

• Diuresis

• Hyperglycemia

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Kalsium & FosforKalsium & Fosfor

• Keduanya membentuk garam appatite didalam tulang & gigi (80-90%).

• Absorpsi paling baik jika perbandingan dalam lumen usus Ca : P = 1 : 1 s/d 1 : 3

• Bila perbandingan > 3, maka absorpsi Ca terhambat (Rachitis).

• Makanan penyebabnya disebut rachitogenik

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Interaksi yang MenghambatInteraksi yang Menghambat

• Beras mengandung asam fitat (P) sehingga mengikat Ca membentuk Ca-fitat.

• Sayuran & buah yang mengandung asam oksalat juga akan menghambat absorpsi Ca.

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Fungsi CaFungsi Ca

• Penggumpalan darah• Kontraksi otot• Penghantar stimulus saraf• Aktifitas enzim tertentu• Membentuk hidroksiapatit pada tulang

dan gigi

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Fungsi PFungsi P

• Ikatan fosfat berenergi tinggi ATP, ADP, kreatin-P, PEP, dll.

• Komponen membran sel fosfolipid• Membentuk hidroksiapatit pada tulang dan

gigi

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Defisiensi CaDefisiensi Ca

• Rickets pada anak-anak• Osteomalacia (osteoporosis) pada dewasa• Tetani / kejang • Postmenopause (estrogen rendah)

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Defisiensi PDefisiensi P

• Gangguan absorpsi di usus• Ekskresi berlebihan melalui ginjal• Sindrom Milkman• Sindrom de Toni Fanconi

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Klor (Cl)Klor (Cl)

• Komponen garam NaCl.• Asam-basa (Chloride shift).• Pengaturan osmotik.• Komponen HCl lambung.• Ekskresi melalui keringat.• Defisiensi Cl menyebabkan alkalosis

metabolik akibat muntah proyektil.

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MagnesiumMagnesium

• Terdapat dalam semua jaringan tubuh.• Komponen ATP.• Berperan dalam sintesis protein.• Berperan dalam kontraksi otot.• Absorpsi usus meningkat bila terdapat Ca,

P, & protein.• Ekskresi melalui ginjal.

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Defisiensi MagnesiumDefisiensi Magnesium

• Terjadi pada alkoholisme/malnutrisi.• Mempengaruhi sistem:

1. kardiovaskuler2. ginjal

3. neuromuskuler

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Fluor (F)Fluor (F)

• Komponen jaringan keras, tu gigi.• Melindungi email gigi.• Fluor bersifat racun thd enolase (glikolisis)• Air PAM mengandung fluor 1 -2 ppm.• Defisiensi fluor --> karies dentis.• Kelebihan fluor --> fluorosis (mottled enamel)

= cekungan-cekungan kuning kecoklatan pada email & dentin

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• Acidosis: plasma pH– Protein damage– CNS depression

• Alkalosis: plasma pH– Hyperexcitability– CNS & heart

• Buffers: HCO3- & proteins

• H+ input: diet & metabolic• H+ output: lungs & kidney

Acid/Base Homeostasis: OverviewAcid/Base Homeostasis: Overview

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Acid/Base Homeostasis: OverviewAcid/Base Homeostasis: Overview

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• Buffers–Blood seconds–Intracellular minutes

• Lung hours

• Kidneys days

Removing Acid or Base

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• pH = pKa + log [HCO3-]/[H2CO3]

• pH = pKa + log [HCO3-]/0.03 x PCO2

• 7.4 = 6.1 + log 20 / 1

• 7.4 = 6.1 + 1.3

• Plasma pH equals 7.4 when buffer ratio is 20/1• The solubility constant of CO2 is 0.03

Henderson-Hasselbalch equationHenderson-Hasselbalch equation

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Physiological Buffer SystemsPhysiological Buffer Systems

• The respiratory system regulation of acid-base balance is a physiological buffering system

• There is a reversible equilibrium between:– Dissolved carbon dioxide and water– Carbonic acid and the hydrogen and

bicarbonate ionsCO2 + H2O H2CO3 H+ + HCO3¯

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Physiological Buffer SystemsPhysiological Buffer Systems

• During carbon dioxide unloading, hydrogen ions are incorporated into water

• When hypercapnia or rising plasma H+ occurs:– Deeper and more rapid breathing expels more

carbon dioxide– Hydrogen ion concentration is reduced

• Alkalosis causes slower, more shallow breathing, causing H+ to increase

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Acid-base disturbancesAcid-base disturbances

• Plasma pH may be affected by a change in either the [bicarbonate] or the PCO2:– When the primary change is in the PCO2, the

disturbance is called respiratory; – When it is the [bicarbonate], it is called

metabolic:

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Acid-base changes in Acid-base changes in acidosis and alkalosisacidosis and alkalosis

Acid-base Disturbance pH HCO3- PCO2

Respiratory acidosis Respiratory alkalosis Metabolic acidosis

Metabolic alkalosis

Thicker arrows indicate primary disorder

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• Metabolic Acidosis: Diabetic ketoacidosis, diarrhea

• Metabolic Alkalosis: antacid, vomiting (will loose Cl too)

• Respiratory Acidosis: Hypoventilation, pulmonary edema, narcotic, chronic bronchitis

• Respiratory Alkalosis: Hyperventilation, asthma, pneumoni, brain injury, anxiety

Clinical Causes …

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CompensationCompensation

• The purpose of the compensation is to return the blood pH to normal

• The change in the PCO2 in the metabolic disorders represents the lung’s role in compensation

• The change in the bicarbonate level represents the kidney’s attempt to compensate for the respiratory acidosis or alkalosis

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Metabolic and Respiratory Acid-Base Changes in Blood

pH pCO2 HCO3-

Acidosis1. Acute metabolic N 2. Compensated metabolic N 3. Acute respiratory N4. Compensated respiratory N

Alkalosis1. Acute metabolic N 2. Chronic metabolic 3. Acute respiratory N4. Compensated respiratory N =decreased; =increased; N=normal

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Normal values for arterial blood gases

Blood Gas Parameter Parameter Reported and Symbol Used

Normal Value

Carbon dioxide tension*

PCO2 35 – 45 mm Hg (average, 40)

Oxygen tension* PO2 80 – 100 mm Hg

Oxygen percent saturation

SO2 97

Hydrogen ion concentration*

pH 7.35 – 7.45

Bicarbonate HCO3- 22 – 26 mmol/L

Arterial Blood Gases (ABG)

* Indicates measured parameter Normal values may differ slightly in exams

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KepustakaanKepustakaan

• Booth, HD. Integrative Physiology II: Fluid and electrolyte balance.PPt. 2004

• Hale, J. Fluid and electrolytes. PPT. 2009.• Hardjasasmita, P. Ikhtisar: biokimia dasar B. Balai Penerbit

FKUI. Jakarta: 50 - 6. 1993.• Ivkovic, A ., Dave, R. Renal review. PPT. 2007• Mineral 2007. website.• Rashid, FA. Respiratory mechanism in acid-base homeostasis. PPT. 2005.