ACID-BASE REGULATION By: Husnil Kadri Biochemistry Departement Medical Faculty Of Andalas University Padang

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    Biochemistry Departement Medical Faculty Of Andalas University Padang

  • *ASAM BASA..pH[H+]

  • *AcidBaseNotasi 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.

  • *Acid-Base BalanceNormal pH of body fluidsArterial blood is 7.4Venous blood and interstitial fluid is 7.35Intracellular fluid is 7.0Alkalosis or alkalemia arterial blood pH rises above 7.45Acidosis or acidemia arterial pH drops below 7.35

  • *Sources of Hydrogen IonsMost hydrogen ions originate from cellular metabolismBreakdown of phosphorus-containing proteins releases phosphoric acid into the ECFAnaerobic respiration of glucose produces lactic acidFat metabolism yields organic acids and ketone bodiesTransporting carbon dioxide as bicarbonate releases hydrogen ions

  • *Acid/Base Homeostasis: Overview

  • *Hydrogen Ion RegulationConcentration of hydrogen ions is regulated sequentially by:Chemical buffer systems act within secondsThe respiratory center in the brain stem acts within 1-3 minutesRenal mechanisms require hours to days to effect pH changes

  • *Chemical Buffer SystemsOne or two molecules that act to resist pH changes when strong acid or base is addedThree major chemical buffer systems Bicarbonate buffer systemPhosphate buffer systemProtein buffer system

  • *1. Bicarbonate Buffer SystemA mixture of carbonic acid (H2CO3) and its salt, sodium bicarbonate (NaHCO3) (potassium or magnesium bicarbonates work as well)If strong acid is added:Hydrogen ions released combine with the bicarbonate ions and form carbonic acid (a weak acid) The pH of the solution decreases only slightly

  • *Bicarbonate Buffer SystemIf strong base is added:It reacts with the carbonic acid to form sodium bicarbonate (a weak base)The pH of the solution rises only slightlyThis system is the only important ECF buffer

  • *2. Phosphate Buffer SystemNearly identical to the bicarbonate system Its components are:Sodium salts of dihydrogen phosphate (H2PO4), a weak acidMonohydrogen phosphate (HPO42), a weak baseThis system is an effective buffer in urine and intracellular fluid

  • *3. Protein Buffer SystemPlasma and intracellular proteins are the bodys most plentiful and powerful buffersSome amino acids of proteins have:Free organic acid groups (weak acids) Groups that act as weak bases (e.g., amino groups)

  • *Buffer SystemsThe respiratory system regulation of acid-base balance is a physiological buffering system

    There is a reversible equilibrium:CO2 + H2O H2CO3 H+ + HCO3

  • *Buffer Systems

    When hypercapnia or rising plasma H+ occurs:Deeper and more rapid breathing expels more carbon dioxideHydrogen ion concentration is reducedAlkalosis causes slower, more shallow breathing, causing H+ to increase

  • *Renal Mechanisms of Acid-Base BalanceChemical buffers can tie up excess acids or bases, but they cannot eliminate them from the bodyThe lungs can eliminate carbonic acid by eliminating carbon dioxideOnly the kidneys can rid the body of metabolic acids (phosphoric, uric, and lactic acids and ketones) and prevent metabolic acidosis

  • *Renal Mechanisms of Acid-Base BalanceThe most important renal mechanisms for regulating acid-base balance are:Conserving (reabsorbing) or generating new bicarbonate ionsExcreting bicarbonate ionsLosing a bicarbonate ion is the same as gaining a hydrogen ion; reabsorbing a bicarbonate ion is the same as losing a hydrogen ion

  • *Kidney Hydrogen Ion Balancing: Proximal TubuleFigure 20-21: Proximal tubule secretion and reabsorption of filtered HCO3-

  • *Reabsorption of Bicarbonate

  • *Hydrogen Ion Excretion

  • *Ammonium Ion ExcretionThis method uses ammonium ions produced by the metabolism of glutamine in PCT cellsEach glutamine metabolized produces two ammonium ions and two bicarbonate ions Bicarbonate moves to the blood and ammonium ions are excreted in urine

  • *Ammonium Ion Excretion

  • *Bicarbonate Ion SecretionWhen the body is in alkalosis, type B intercalated cells:Exhibit bicarbonate ion secretionReclaim hydrogen ions and acidify the bloodThe mechanism is the opposite of type A intercalated cells and the bicarbonate ion reabsorption processEven during alkalosis, the nephrons and collecting ducts excrete fewer bicarbonate ions than they conserve

  • Kidney Hydrogen Ion Balancing: Collecting Duct

  • *SourcesAchmadi, A., George, YWH., Mustafa, I. Pendekatan Stewart Dalam Fisiologi Keseimbangan Asam Basa. 2007Beaudoin, D. Electrolytes and ion sensitive electrodes. PPT. 2003.Ivkovic, A ., Dave, R. Renal review. PPTKersten. Fluid and electrolytes. PPT.Marieb, EN. Fluid, electrolyte, and acid-base balance. PPT. Pearson Education, Inc. 2004Rashid, 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. 2004Smith, SW. Acid-Base Disorders.