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REGULATION OF ACID-BASE & ELECTROLYTES

REGULATION OF ACID-BASE & ELECTROLYTES. Oleh: Dr. Husnil Kadri, M.Kes Bagian Biokimia Fakultas Kedokteran Universitas Andalas Padang. ASAM BASA. [H + ]. pH. pH. pH. Acid. Base.

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REGULATION OF ACID-BASE & ELECTROLYTES

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  1. REGULATION OF ACID-BASE &ELECTROLYTES Oleh: Dr. Husnil Kadri, M.Kes Bagian Biokimia Fakultas Kedokteran Universitas Andalas Padang

  2. ASAM BASA.. [H+] pH

  3. pH pH Acid Base Notasi pH diciptakan oleh seorang ahli kimia dari Denmark yaitu Soren Peter Sorensen pada thn 1909, yang berarti log negatif dari konsentrasi ion hidrogen. Dalam bahasa Jerman disebutWasserstoffionenexponent (eksponen ion hidrogen) dan diberi simbol pH yang berarti: ‘potenz’ (power) of Hydrogen.

  4. Acid-Base Balance • Normal pH of body fluids • Arterial blood is 7.4 • Venous blood and interstitial fluid is 7.35 • Intracellular fluid is 7.0 • Alkalosis or alkalemia – arterial blood pH rises above 7.45 • Acidosis or acidemia – arterial pH drops below 7.35

  5. Sources of Hydrogen Ions • Most hydrogen ions originate from cellular metabolism • Breakdown of phosphorus-containing proteins releases phosphoric acid into the ECF • Anaerobic respiration of glucose produces lactic acid • Fat metabolism yields organic acids and ketone bodies • Transporting carbon dioxide as bicarbonate releases hydrogen ions

  6. Hydrogen Ion Regulation • Concentration of hydrogen ions is regulated sequentially by: • Chemical buffer systems – act within seconds • The respiratory center in the brain stem – acts within 1-3 minutes • Renal mechanisms – require hours to days to effect pH changes

  7. Acid/Base Homeostasis: Overview

  8. Regulation of Blood pH • The lungs and kidneys play important role in regulating blood pH. • The lungs regulate pH through retention or elimination of CO2 by changing the rate and volume of ventilation. • The kidneys regulate pH by excreting acid, primarily in the ammonium ion (NH4+), and by reclaiming HCO3- from the glomerular filtrate (and adding it back to the blood).

  9. Carbonic acid/bicarbonate buffer system • Carbonic acid is formed when CO2 combines with water. This reaction is catalysed by carbonic anhydrase • Carbonic acid dissociates spontaneously to form a proton and a bicarbonate ion CO2 + H2O  H2CO3 H+ + HCO3- CA

  10. The Lung Regulation • Normal, unassisted breathing: • An increase in arterial PCO2 acts through the respiratory centre to increase the rate of pulmonary ventilation • A decrease in arterial PCO2reduces the rate of ventilation • Assisted breathing: • A respirator is used to assist breathing by expelling CO2, thus reducing PCO2 in blood

  11. The Lung Regulation • 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

  12. The Lung Regulation

  13. The Renal Regulation • Chemical buffers can tie up excess acids or bases, but they cannot eliminate them from the body • The lungs can eliminate carbonic acid by eliminating carbon dioxide • Only the kidneys can rid the body of metabolic acids (phosphoric, uric, and lactic acids and ketones) and prevent metabolic acidosis

  14. The Renal Regulation • The most important renal mechanisms for regulating acid-base balance are: • Conserving (reabsorbing) or generating new bicarbonate ions • Excreting bicarbonate ions • Losing a bicarbonate ion is the same as gaining a hydrogen ion; reabsorbing a bicarbonate ion is the same as losing a hydrogen ion

  15. Reabsorption of Bicarbonate

  16. Hydrogen Ion Excretion

  17. Hendersen-Hasselbalch(1909) CARA TRADISIONAL :

  18. HCO3 HCO3 [HCO3-] BASA GINJAL Normal pH = 6.1 + log Kompensasi CO2  pCO2 PARU ASAM CO2 Normal

  19. Carbonic acid/bicarbonate buffer system pKa = 6.1 • The pKa of carbonic acid is 6.1 • Carbonic acid is the major buffer in ECF • The pH of blood can be determined using the Henderson-Hasselbalch equation H2CO3 H+ + HCO3- ECF: Carbonic acid Bicarbonate ion

  20. Henderson-Hasselbalch equation • 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

  21. Cara Stewart ; DUA VARIABEL pH atau [H+] DALAM PLASMA DITENTUKAN OLEH VARIABEL INDEPENDEN VARIABEL DEPENDEN • Stewart PA. Can J Physiol Pharmacol 61:1444-1461, 1983.

  22. VARIABEL INDEPENDEN CO2 STRONG ION DIFFERENCE WEAK ACID pCO2 SID Atot

  23. CO2 • Rx dominandari CO2adalahrxabsorpsi OH-hasildisosiasi air denganmelepas H+. • Semakintinggi pCO2semakinbanyak H+ yang terbentuk. • Iniygmenjadidasardariterminologi “respiratory acidosis,” yaitupelepasan ion hidrogenakibat pCO2 CO2Didalam plasma beradadalam 4 bentuk • sCO2 (terlarut) • H2CO3asamkarbonat • HCO3- ion bikarbonat • CO32- ion karbonat

  24. STRONG ION DIFFERENCE Definisi: Strong ion difference adalah ketidakseimbangan muatan dari ion-ion kuat. Lebih rinci lagi, SID adalah jumlah konsentrasi basa kation kuat dikurangi jumlah dari konsentrasi asam anion kuat. Untuk definisi ini semua konsentrasi ion-ion diekspresikan dalam ekuivalensi (mEq/L). Semua ion kuat akan terdisosiasi sempurna jika berada didalam larutan, misalnya ion natrium (Na+), atau klorida (Cl-). Karena selalu berdisosiasi ini maka ion-ion kuat tersebut tidak berpartisipasi dalam reaksi-reaksi kimia. Perannya dalam kimia asam basa hanya pada hubungan elektronetraliti.

  25. STRONG ION DIFFERENCE Gamblegram Mg++ Ca++ K+ 4 SID Na+ 140 Cl- 102 [Na+] + [K+] + [kation divalen] - [Cl-] - [asam organik kuat-] [Na+] + [K+] - [Cl-] = [SID] 140 mEq/L + 4 mEq/L - 102 mEq/L = 34 mEq/L KATION ANION

  26. SKETSA HUBUNGAN ANTARA SID,H+ DAN OH- [H+] [OH-] Konsentrasi [H+] Asidosis Alkalosis SID (–) (+) Dalam cairan biologis (plasma) dgn suhu 370C, SID hampir selalu positif, biasanya berkisar 30-40 mEq/Liter

  27. WEAK ACID [Protein-] + [H+] [Protein H] Kombinasi protein dan posfat disebut asam lemah total (total weak acid)  [Atot]. Reaksi disosiasinya adalah: disosiasi [Atot] (KA) = [A-].[H+]

  28. Gamblegram Mg++ HCO3- 24 Ca++ K+ 4 SID Na+ 140 Weak acid (Alb-,P-) Cl- 102 KATION ANION

  29. DEPENDENT VARIABLES H+ HCO3- OH- AH CO3- A-

  30. INDEPENDENT VARIABLES DEPENDENT VARIABLES Strong Ions Difference pH pCO2 Protein Concentration

  31. APLIKASI H3O+ = H+ = 40 mEq/L HCO3-  HCO3- HCO3- HCO3 = 24 Na 140 K SID Mg SID n Ca SID  Alb P Alb Cl 115 Laktat/keto=UA P Alb Cl 102 Cl 102 P CL 95 Asidosis hiperkloremi Keto/laktat asidosis Alkalosis hipokloremi KATION ANION

  32. KLASIFIKASI GANGGUAN KESEIMBANGAN ASAM BASA BERDASARKAN PRINSIP STEWART Fencl V, Jabor A, Kazda A, Figge J. Diagnosis of metabolic acid-base disturbances in critically ill patients. Am J Respir Crit Care Med 2000 Dec;162(6):2246-51

  33. ASIDOSIS ALKALOSIS I. Respiratori  PCO2  PCO2 II. Nonrespiratori (metabolik) 1. Gangguan pd SID a. Kelebihan / kekurangan air  [Na+],  SID  [Na+],  SID b. Ketidakseimbangan anion kuat:  [Cl-],  SID  [Cl-],  SID i. Kelebihan / kekurangan Cl- ii. Ada anion tak terukur  [UA-],  SID 2. Gangguan pd asam lemah i. Kadar albumin  [Alb]  [Alb] ii. Kadar posphate  [Pi]  [Pi] KLASIFIKASI Fencl V, Jabor A, Kazda A, Figge J. Diagnosis of metabolic acid-base disturbances in critically ill patients. Am J Respir Crit Care Med 2000 Dec;162(6):2246-51

  34. RESPIRASI M E T A B O L I K Abnormal pCO2 Abnormal SID Abnormal Weak acid Alb PO4-  Anion kuat AIR Cl- UA- Turun Alkalosis Turun kekurangan Hipo Asidosis Meningkat kelebihan Hiper Positif meningkat Fencl V, Am J Respir Crit Care Med 2000 Dec;162(6):2246-51

  35. Anion Gap • Described by Gamble in 1939 • Electroneutrality • Na+, Cl-, and HCO3 are measured ions Na + UC = Cl + HCO3 + UA UC= Sum of unmeasured cations UA = Sum of unmeasured anions

  36. Unmeasured Cations: total 11 mEq/L Potassium 4 Calcium 5 Magnesium 2 Unmeasured Anions: total 23 mEq/L Sulfates 1 Phosphates 2 Albumin 16 Lactic acid 1 Org. acids 3 Anion Gap

  37. Anion Gap Na + UC = Cl + HCO3 + UA 140 + 11 = 104 + 24 + 23 151 = 151 UA – UC = Na - (Cl + HCO3); Anion Gap = Na - (Cl + HCO3)

  38. Change in Anion Gap vs HCO3 • In simple AG Metabolic Acidosis • decrease in plasma bicarbonate = increase in AG Anion Gap = 1 HCO3 • Helpful in identifying mixed disorders

  39. Sources • Achmadi, A., George, YWH., Mustafa, I. Pendekatan “Stewart” Dalam Fisiologi Keseimbangan Asam Basa. 2007 • Beaudoin, D. Electrolytes and ion sensitive electrodes. PPT. 2003. • Ivkovic, A ., Dave, R. Renal review. PPT • Kersten. Fluid and electrolytes. PPT. • Marieb, EN. Fluid, electrolyte, and acid-base balance. PPT. Pearson Education, Inc. 2004 • Rashid, FA. Respiratory mechanism in acid-base homeostasis. PPT. 2005. • Silverthorn, DU. Integrative Physiology II: Fluid and Electrolyte Balance. Chapter 20, part B. Pearson Education, Inc. 2004 • Smith, SW. Acid-Base Disorders. www.acid-base.com

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