Nephrology Book

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Acid-Base Homeostasis

Aka: Acid-Base Homeostasis, Acid-Base Equilibrium, Blood pH, Hydrogen Ion
  1. See Also
    1. Arterial Blood Gas
    2. ABG Interpretation
    3. A-a Gradient
    4. Anion Gap
    5. Respiratory Physiology
  2. Physiology: Blood pH and Buffering Systems in General
    1. pH is a measure of Hydrogen Ion concentration
      1. pH=log (1/H)
        1. Where H is Hydrogen Ion concentration in gram moles per liter
      2. Neutral pH in water
        1. Hydrogen Ion is typically 10^-7 and is balanced by 10^-7 hydroxyl ion (OH)
      3. Body pH
        1. Normal arterial pH is 7.40
        2. Gastric Acid pH <3
        3. Pancreatic Secretion pH >8
    2. Blood pH is normally maintained between 7.35 and 7.45 via buffers
      1. Weak acids buffer pH in a narrow range near 7.40
        1. Weak base (WB-) bound to Hydrogen Ions (H+) dissociate when a strong acid (SA) is present
        2. H+WB- => H+SA + WB-
      2. Extracellular buffers
        1. Bicarbonate buffering system is the main extracellular buffer
        2. CO2 + H2O <=> H2CO3 <=> HCO3- + H+
      3. Intracellular buffers
        1. Intracellular proteins, ammonia and phosphates
        2. Ammonia buffering system
          1. Ammonia (weak base) + Hydrogen Ion => Ammonium (NH3- + H+ => NH4)
          2. Glutamine is metabolized in renal tubule cells to Ammonium and bicarbonate
          3. Ammonium (NH4) is excreted in urine, while bicarbonate is reabsorbed in capillaries
        3. Phosphate buffering system
          1. Hydrogen phosphate + Hydrogen Ion => Dihydrogen Phosphate (HPO4 + H+ => H2PO4)
          2. Dihydrogen Phosphate (H2PO4) is excreted in urine
      4. Images: Acid Base Homeostasis
        1. acidBaseHomeostasis.png
    3. Low Electrolyte concentrations (Sodium, Potassium, chloride) decrease Hydrogen Ion concentration (Metabolic Alkalosis)
      1. Hyponatremia
        1. Increased Sodium reabsorption results in secretion of the hydrogen cation in exchange
        2. Bicarbonate absorption increases with Sodium reabsorption
        3. Aldosterone increases with Hyponatremia resulting in further Hydrogen Ion secretion
      2. Hypokalemia
        1. When Potassium is at normal level, it is excreted in exchange for Sodium
        2. When Potassium is reabsorbed in Hypokalemia, another cation is needed to exchange for Sodium
        3. In this case of Hypokalemia, Hydrogen Ion is secreted in exchange for Sodium absorption
      3. Hypochloremia
        1. Chloride is not available for reabsorption with Sodium from the renal tubule
        2. Another cation, in this case Hydrogen Ion, is secreted to balance negatively charged lumen
  3. Physiology: Bicarbonate buffering system (CO2-HCO3-)
    1. Bicarbonate buffering system equation
      1. CO2 + H2O <=> H2CO3 <=> HCO3- + H+
      2. Presence of strong acid shifts equation left toward CO2 + H2O
      3. Presence of strong base shifts equation right toward HCO3- and H+ ion
    2. Buffering Equation describes a balance between bicarbonate (HCO3-) and carbon dioxide (CO2)
      1. Water (H2O) combines with carbon dioxide (CO2) to form carbonic acid (H2CO3) catalyzed by carbonic anhydrase
      2. Carbonic acid (H2CO3) may freely dissociate with Hydrogen Ion (H+) to form bicarbonate (HCO3-)
      3. Under normal conditions blood bicarbonate (HCO3-) to dissolved CO2 ratio is 20:1
    3. pH and Hydrogen Ion (H+) are proportional to HCO3-/pCO2
      1. H+ : HCO3-/ pCO2
      2. Henderson-Hasselbach equation
        1. pH = 6.1 + log10 (HCO3-/CO2)
      3. Hydrogen Ion increases (and pH decreases)
        1. Increased pCO2 (Respiratory Acidosis) OR
        2. Decreased HCO3- (Metabolic Acidosis)
      4. Hydrogen Ion decreases (and pH increases)
        1. Decreased pCO2 (Respiratory Alkalosis) OR
        2. Increased HCO3- (Metabolic Alkalosis)
    4. Homeostasis is maintained via respiratory (pCO2) and renal (HCO3-) mechanisms
      1. Lung function maintains pCO2 near 40 mmHg
        1. CO2 is a weak acid, and is the only acid excreted by the lung (all other acids are renally excreted)
        2. Brainstem responds to increased CO2 and H+ ion levels to increase Respiratory Rate reflexively
        3. Low oxygen level (O2) stimulates carotid and aortic body receptors (CN 9/10) to increase Respiratory Rate
      2. Renal Function maintains bicarbonate (HCO3-) near 25 mEq/L
        1. Bicarbonate is filtered by glomerulus and reabsorbed in renal tubules combined with Hydrogen Ion
        2. Total extracellular bicarbonate is 350 mEq for a 70 kg male
        3. Renal tubules excrete Hydrogen Ion
        4. Urine tends to be acidic (due to excess acid production over base production daily)
    5. Bicarbonate gains or losses impacts acidosis
      1. Bicarbonate loss (e.g. Diarrhea) results in an increase in Hydrogen Ion (acidosis)
      2. Hydrogen Ion loss (e.g. Vomiting) results in bicarbonate gain (alkalosis)
  4. Physiology: Acid generation via metabolism
    1. Carbohydrate and fat metabolism generates large amounts of CO2
      1. CO2 is quickly eliminated via respiration
    2. Protein is metabolized into nonvolatile acid (fixed acid)
      1. Fixed Acid generated cannot be excreted as CO2
      2. Fixed Acid is buffered with bicarbonate to form carbonic acid
      3. Hydrogen Ion is renally excreted, maintaining bicarbonate for further buffering
  5. Physiology: Renal Maintenance of Bicarbonate
    1. Bicarbonate is freely filtered by the glomerulus and reabsorbed by proximal tubule
      1. Glomerulus loses ~3600 meq bicarbonate daily (given 100 ml/min GFR) that must be reclaimed
      2. Nearly all bicarbonate is reabsorbed by the proximal tubule
        1. Bicarbonate levels above 26 mEq/L cannot be completely reabsorbed by proximal tubule
      3. Bicarbonate reabsorption (Metabolic Alkalosis) is increased with specific triggers
        1. Volume depletion (known as contraction alkalosis)
        2. Angiotensin II increased levels
        3. pCO2 increased levels (compensates for Respiratory Acidosis)
        4. Hypokalemia
      4. Renal Tubular Acidosis Type II results from defective proximal tubule reabsorption
        1. Causes Metabolic Acidosis through bicarbonate loss
    2. Hydrogen Ion renal excretion
      1. Primary mechanism for excreting fixed acid (see protein metabolism above)
      2. Proton Pump (ATP fueled)
        1. Pumps one Hydrogen Ion into collecting tubule
        2. Releases one bicarbonate to pass freely back into capillaries in the renal interstitium
        3. Renal Tubular Acidosis Type I (distal) results from defective Hydrogen Ion pump
      3. Glutamine Hydrolysis (proximal tubule)
        1. Renal key mechanism to compensate for acidosis (more than Hydrogen Ion excretion)
        2. Results in two outputs
          1. Ammonium (NH4+) which is excreted into urine
          2. Bicarbonate (HCO3-) which is absorbed by capillaries
  6. Physiology: Images
    1. Acid Base Homeostasis
      1. acidBaseHomeostasis.png
    2. Nephron
      1. nephron.png
  7. Resources
    1. Acid-Base Interpreter
      1. https://fpnotebook.com/_media/acidbaseapp.html
  8. References
    1. Goldberg (2014) Clinical Physiology, Medmaster, Miami, p. 27-31
    2. Marino (2014) ICU Book, p. 587-99
    3. Preston (2011) Acid-Base Fluids and Electrolytes, p. 3-30
    4. Rose (1989) Clinical Physiology of Acid-Base and Electrolyte Disorders, p. 261-85

Acid-Base Equilibrium (C0001117)

Definition (MSHCZE) rovnováha mezi kyselinami a zásaditými látkami v těle, tj. mezi jejich tvorbou na jedné straně a vylučováním na straně druhé. Její přesné udržení v určitém rozmezí je nezbytné pro správnou činnost organismu. K mechanismům, které větší výkyvy minimalizují, patří jednak pufry (nárazníky, tlumivé roztoky) vyrovnávající okamžité změny, jednak plíce a ledviny, které mohou poruchy kompenzovat po dlouhou dobu. Za normálních okolností má organismus tendenci se okyselovat – kyselé látky však dokáže pufrovat a vyloučit močí, která je proto obvykle kyselá, oxid uhličitý pak vydýchat plícemi. Porucha rovnováhy ve prospěch kyselin vede k acidóze, porucha ve prospěch zásaditých látek k alkalóze. Oba typy poruchy mohou být vyvolány buď metabolickými ději - (metabolická acidóza či alkalóza), nebo jsou důsledkem poruchy dýchání (respirační acidóza či alkalóza). K vyhodnocení ABR se užívá Astrupovo vyšetření. (cit. Velký lékařský slovník online, 2013 http://lekarske.slovniky.cz/ )
Definition (NCI_NCI-GLOSS) In medicine, the state of having the right amount of acid and base in the blood and other body fluids. Keeping a normal acid-base equilibrium is important for the body to work the way it should.
Definition (NCI) pH homeostasis is one of numerous control systems that are involved in keeping the body's internal milieu consistent within a narrow range of variation and are important to the continuation of life. Important homeostatic mechanisms in the maintenance of blood pH include the buffering action of bicarbonate, and the actions of the renal-respiratory system. (from NCI)
Definition (MSH) The balance between acids and bases in the BODY FLUIDS. The pH (HYDROGEN-ION CONCENTRATION) of the arterial BLOOD provides an index for the total body acid-base balance.
Definition (CSP) balance between acids and bases in body fluids; balance is achieved by the offset of the ingestion and production of acidic and basic material and by the amount of acidic and basic material metabolized and excreted by the body.
Concepts Physiologic Function (T039)
MSH D000136
SnomedCT 78049003
English Acid Base Equilibrium, Acid-Base Equilibrium, Equilibrium, Acid-Base, Acid Base Balance, Acid-Base Balance, Balance, Acid-Base, Acid / base balance, Acid-base equilibrium, function, acid balance base, acid balance bases, acid base balance, equilibrium acid-base, acid balance based, acid base balances, acid based equilibrium, acid based balance, acid-base balance, acid-base equilibrium, acid base equilibrium, Acid-base equilibrium, Acid-base equilibrium, function (observable entity), Acid-base equilibrium (function), pH Homeostasis
Swedish Syra-bas-jämvikt
Czech acidobazická rovnováha, ABR
Finnish Happo-emästasapaino
French Équilibre acido-basique, Équilibre acide-base, Équilibre acidobasique
Italian Bilanciamento acido-base, Equilibrio acido-base
Russian KISLOTNO-SHCHELOCHNOE RAVNOVESIE, КИСЛОТНО-ЩЕЛОЧНОЕ РАВНОВЕСИЕ
Spanish Equilibrio Ácido-Base, Equilibrio Acidobásico, Equilibrio Ácido-Básico, equilibrio acidobásico (entidad observable), equilibrio acidobásico (función), equilibrio acidobásico, equilibrio ácido-base
Portuguese Equilíbrio Ácido-Base, Equilíbrio Acidobásico, Equilíbrio Ácido-Básico
Croatian ACIDOBAZNA RAVNOTEŽA
Polish Równowaga kwasowo-zasadowa
Japanese アニオンギャップ, 酸塩基平衡
Norwegian Syre-basebalanse
German Säure-Basen-Gleichgewicht
Dutch Evenwicht, zuur-base-, Zuur-base-evenwicht
Sources
Derived from the NIH UMLS (Unified Medical Language System)


Hydrogen-Ion Concentration (C0020283)

Definition (MSH) The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH = log 1/2[1/(H+)], where (H+) is the hydrogen ion concentration in gram equivalents per liter of solution. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)
Definition (MSH) The log 1/2[1/(H+)], where (H+) is the hydrogen ion concentration in gram equivalents per liter of solution. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)
Definition (HL7V3.0) <p>pH(1 mol/l)</p>
Definition (NCI_CDISC) The negative logarithm (base 10) of the concentration of hydronium ions, which is used as a measure of the acidity or alkalinity of a fluid.
Definition (NCI) Quantity of dimension one used to express on a scale from 0 to 14 the amount-of-substance concentration of hydrogen ion of dilute aqueous solution, calculated as the logarithm of the reciprocal of hydrogen-ion concentration in gram atoms per liter.
Concepts Quantitative Concept (T081)
MSH D006863
SnomedCT 27327002
HL7 [PH]
LNC LP14752-7, MTHU001949
English Concentration, Hydrogen-Ion, Concentrations, Hydrogen-Ion, Hydrogen Ion Concentration, Hydrogen-Ion Concentration, Hydrogen-Ion Concentrations, hydrogen ion concentration, potential of Hydrogen, H+ concentration, H<sup>+</sup> concentration, pH, pH NOS, ph, hydrogen-Ion concentration (pH), Hydrogen-ion concentration, [pH], PH, Hydrogen ion concentration, H^+^ concentration, Hydrogen ion concentration (function), Hydrogen ion concentration (observable entity), Hydrogen ion concentration, function (observable entity)
Dutch pH NAO, Waterstofionenconcentratie, pH
French pH SAI, Concentration des ions d'hydrogène, pH, Concentration en protons, Concentration en ions d'hydrogène, Concentration des protons
German pH NNB, pH, Wasserstoffionenkonzentration
Italian pH NAS, Concentrazione idrogenionica, pH
Portuguese pH NE, pH, Concentração de Íons de Hidrogênio
Spanish pH NEOM, concentración de protones, concentración de ion hidrógeno, concentración de ion hidrógeno (entidad observable), concentración de H+, concentración de H<sup>+</sup>, pH, concentración de H^+^, concentración de ion hidrógeno (función), concentración de hidrogeniones, concentración de hidrogeniones (entidad observable), Concentración de Iones de Hidrógeno
Japanese pH, pHNOS, pH, pHNOS
Swedish Vätejonkoncentration
Finnish Vetyionipitoisuus
Russian VODORODNYI POKAZATEL', VODORODNYKH IONOV KONTSENTRATSIIA, PH, ВОДОРОДНЫЙ ПОКАЗАТЕЛЬ, ВОДОРОДНЫХ ИОНОВ КОНЦЕНТРАЦИЯ
Czech pH NOS, hodnota pH, vodíkové ionty - koncentrace, pH, vodíkový exponent, koncentrace vodíkových iontů
Croatian pH, VODIKOVI IONI, KONCENTRACIJA, KONCENTRACIJA VODIKOVIH IONA
Polish Stężenie jonów wodorowych, pH, Jony wodorowe
Hungarian pH, pH k.m.n.
Norwegian Not Translated[Hydrogen-Ion Concentration]
Sources
Derived from the NIH UMLS (Unified Medical Language System)


Blood pH (C0853363)

Concepts Laboratory Procedure (T059)
CPT 82803, 82800, 82805
Italian pH ematico, pH ematico NAS
Dutch bloed pH NAO, bloed pH
French pH sanguin SAI, pH sanguin
German pH im Blut NNB, pH im Blut
Portuguese pH do sangue NE, pH do sangue
Spanish pH sanguíneo NEOM, pH sanguíneo
Japanese 血液pHNOS, 血液pH, ケツエキpH, ケツエキpHNOS
English Blood pH, Blood pH NOS, ph blood, blood ph, Analysis of pH of blood
Czech pH krve, pH krve NOS
Hungarian Vér pH k.m.n., Vér pH
Sources
Derived from the NIH UMLS (Unified Medical Language System)


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