Bicarbonate buffer system - wikipedia Bicarbonate buffer system Carbon dioxide, a by - product of cellular respiration, is dissolved in the blood, where it is taken up by red blood cells and converted to carbonic acid by carbonic anhydrase. Most of the carbonic acid then dissociates to bicarbonate and hydrogen ions. The bicarbonate buffer system is an acid - base homeostatic mechanism involving the balance of carbonic acid ( H CO ), bicarbonate ion ( HCO − 3 ), and carbon dioxide ( CO ) in order to maintain pH in the blood and duodenum, among other tissues, to support proper metabolic function. Catalyzed by carbonic anhydrase, carbon dioxide ( CO ) reacts with water ( H O ) to form carbonic acid ( H CO ), which in turn rapidly dissociates to form a bicarbonate ion ( HCO − 3 ) and a hydrogen ion ( H ) as shown in the following reaction : C O 2 + H 2 O ⇄ H 2 C O 3 ⇄ H C O 3 − + H + ( displaystyle ( \rm ( CO_ ( 2 ) + H_ ( 2 ) O \rightleftarrows H_ ( 2 ) CO_ ( 3 ) \rightleftarrows HCO_ ( 3 ) ^ ( - ) + H ^ ( + ) ) ) ) As with any buffer system, the pH is balanced by the presence of both a weak acid ( for example, H CO ) and its conjugate base ( for example, HCO − 3 ) so that any excess acid or base introduced to the system is neutralized. Failure of this system to function properly results in acid - base imbalance, such as acidemia ( pH < 7.35 ) and alkalemia ( pH > 7.45 ) in the blood. Contents 1 In systemic acid -- base balance 1.1 Regulation 1.2 Henderson -- Hasselbalch equation 1.3 Derivation of the Kassirer - Bleich approximation 2 In other tissues 3 References 4 External links In systemic acid -- base balance In tissue, cellular respiration produces carbon dioxide as a waste product ; as one of the primary roles of the cardiovascular system, most of this CO is rapidly removed from the tissues by its hydration to bicarbonate ion. The bicarbonate ion present in the blood plasma is transported to the lungs, where it is dehydrated back into CO and released during exhalation. These hydration and dehydration conversions of CO and H CO, which are normally very slow, are facilitated by carbonic anhydrase in both the blood and duodenum. While in the blood, bicarbonate ion serves to neutralize acid introduced to the blood through other metabolic processes ( e.g. lactic acid, ketone bodies ) ; likewise, any bases ( e.g. urea from the catabolism of proteins ) are neutralized by carbonic acid. Regulation As calculated by the Henderson - Hasselbalch equation, in order to maintain a normal pH of 7.4 in the blood ( whereby the pKa of carbonic acid is 6.1 at physiological temperature ), a 20 : 1 bicarbonate to carbonic acid must constantly be maintained ; this homeostasis is mainly mediated by pH sensors in the medulla oblongata of the brain and probably in the kidneys, linked via negative feedback loops to effectors in the respiratory and renal systems. In the blood of most animals, the bicarbonate buffer system is coupled to the lungs via respiratory compensation, the process by which the rate of breathing changes to compensate for changes in the blood concentration of CO. By Le Chȃtelier 's Principle, the release of CO from the lungs pushes the reaction above to the left, causing carbonic anhydrase to form CO until all excess acid is removed. Bicarbonate concentration is also further regulated by renal compensation, the process by which the kidneys regulate the concentration of bicarbonate ions by excreting H ions into the urine while, at the same time, secreting HCO − 3 ions into the blood plasma, or vice versa, depending on whether the plasma pH is falling or rising, respectively. Henderson -- Hasselbalch equation A modified version of the Henderson -- Hasselbalch equation can be used to relate the pH of blood to constituents of the bicarbonate buffer system : p H = p K a H 2 C O 3 + log ⁡ ( ( H C O 3 − ) ( H 2 C O 3 ) ) ( displaystyle pH = pK_ ( a ~ H_ ( 2 ) CO_ ( 3 ) ) + log left ( ( \frac ( ( HCO_ ( 3 ) ^ ( - ) ) ) ( ( H_ ( 2 ) CO_ ( 3 ) ) ) ) \right ) ), where : pK is the negative logarithm ( base 10 ) of the acid dissociation constant of carbonic acid. It is equal to 6.1. ( HCO − 3 ) is the concentration of bicarbonate in the blood ( H CO ) is the concentration of carbonic acid in the blood This is useful in arterial blood gas, but these usually state pCO, that is, the partial pressure of carbon dioxide, rather than H CO. However, these are related by the equation : ( H 2 C O 3 ) = k H C O 2 × p C O 2 ( displaystyle ( H_ ( 2 ) CO_ ( 3 ) ) = k_ ( \rm ( H ~ CO_ ( 2 ) ) ) , \times pCO_ ( 2 ) ), where : ( H CO ) is the concentration of carbonic acid in the blood k is a constant including the solubility of carbon dioxide in blood. k is approximately 0.03 ( mmol / L ) / mmHg pCO is the partial pressure of carbon dioxide in the blood Taken together, the following equation can be used to relate the pH of blood to the concentration of bicarbonate and the partial pressure of carbon dioxide : p H = 6.1 + log ⁡ ( ( H C O 3 − ) 0.03 × p C O 2 ) ( displaystyle pH = 6.1 + log left ( ( \frac ( ( HCO_ ( 3 ) ^ ( - ) ) ) ( 0.03 \times pCO_ ( 2 ) ) ) \right ) ), where : pH is the acidity in the blood ( HCO − 3 ) is the concentration of bicarbonate in the blood, in mmol / L pCO is the partial pressure of carbon dioxide in the blood, in mmHg Derivation of the kassirer - bleich approximation The Henderson Equation, which is derived from the Law of Mass Action, can be modified with respect to the bicarbonate buffer system to yield a simpler equation that provides a quick approximation of the H or HCO − 3 concentration without the need to calculate logarithms : K a, H 2 C O 3 = ( H C O 3 − ) ( H 3 O + ) ( H 2 C O 3 ) ( displaystyle ( \rm ( K_ ( a, H_ ( 2 ) CO_ ( 3 ) ) = ( \frac ( ( HCO_ ( 3 ) ^ ( - ) ) ( H_ ( 3 ) O ^ ( + ) ) ) ( ( H_ ( 2 ) CO_ ( 3 ) ) ) ) ) ) ) Since the partial pressure of carbon dioxide is much easier to obtain from measurement than carbonic acid, the Henry 's Law solubility constant -- which relates the partial pressure of a gas to its solubility -- for CO in plasma is used in lieu of the carbonic acid concentration. After rearranging the equation and applying Henry 's Law, the equation becomes : ( H + ) = K ′ ⋅ 0.03 P C O 2 ( H C O 3 − ) ( displaystyle ( \rm ( ( H ^ ( + ) ) = ( \frac ( K ' cdot 0.03 P_ ( CO_ ( 2 ) ) ) ( ( HCO_ ( 3 ) ^ ( - ) ) ) ) ) ) ) Where K ' is the dissociation constant from the pK of carbonic acid, 6.1, which is equal to 800nmol / L ( since K ' = 10 = 10 ≈ 8.00 X10 mol / L = 800nmol / L ). By multiplying K ' ( expressed as nmol / L ) and 0.03 ( 800 X 0.03 = 24 ) and rearranging with respect to HCO − 3, the equation is simplified to : ( H C O 3 − ) = 24 P C O 2 ( H + ) ( displaystyle ( \rm ( ( HCO_ ( 3 ) ^ ( - ) ) = 24 ( \frac ( P_ ( CO_ ( 2 ) ) ) ( ( H ^ ( + ) ) ) ) ) ) ) In other tissues The bicarbonate buffer system plays a vital role in other tissues as well. In the human stomach and duodenum, the bicarbonate buffer system serves to both neutralize gastric acid and stabilize the intracellular pH of epithelial cells via the secretion of bicarbonate ion into the gastric mucosa. In patients with duodenal ulcers, Helicobacter pylori eradication can restore mucosal bicarbonate secretion, and reduce the risk of ulcer recurrence. References ^ Jump up to : Krieg, Brian J. ; Taghavi, Seyed Mohammad ; Amidon, Gordon L. ; Amidon, Gregory E. ( 2014 - 11 - 01 ). `` In Vivo Predictive Dissolution : Transport Analysis of the CO2, Bicarbonate In Vivo Buffer System ''. Journal of Pharmaceutical Sciences. 103 ( 11 ) : 3473 -- 3490. ISSN 1520 - 6017. doi : 10.1002 / jps. 24108. Jump up ^ Oxtoby, David W. ; Gillis, Pat ( 2015 ). `` Acid - base equilibria ''. Principles of Modern Chemistry ( 8 ed. ). Boston, MA : Cengage Learning. pp. 611 -- 753. ISBN 1305079116. Jump up ^ Widmaier, Eric ; Raff, Hershel ; Strang, Kevin ( 2014 ). `` The kidneys and regulation of water and inorganic ions ''. Vander 's Human Physiology ( 13 ed. ). New York, NY : McGraw - Hill. pp. 446 -- 489. ISBN 0073378305. Jump up ^ Meldrum, N.U. ; Roughton, F.J.W. ( 1933 - 12 - 05 ). `` Carbonic anhydrase. Its preparation and properties ''. The Journal of Physiology. 80 ( 2 ) : 113 -- 142. ISSN 0022 - 3751. PMC 1394121. PMID 16994489. doi : 10.1113 / jphysiol. 1933. sp003077. Jump up ^ Rhoades, Rodney A. ; Bell, David R. ( 2012 ). Medical physiology : principles for clinical medicine ( 4th ed., International ed. ). Philadelphia, Pa. : Lippincott Williams & Wilkins. ISBN 9781451110395. Jump up ^ al. ), David Sadava... ( et ; Bell, David R. ( 2014 ). Life : The Science of Biology ( 10th ed. ). Sunderland, MA : Sinauer Associates. ISBN 9781429298643. ^ Jump up to : Bear, R.A. ; Dyck, R.F. ( 1979 - 01 - 20 ). `` Clinical approach to the diagnosis of acid - base disorders. ''. Canadian Medical Association Journal. 120 ( 2 ) : 173 -- 182. ISSN 0008 - 4409. PMC 1818841. PMID 761145. Jump up ^ Nelson, David L. ; Cox, Michael M. ; Lehninger, Albert L ( 2008 ). Lehninger Principles of Biochemistry ( 5th ed. ). New York : W.H. Freeman. ISBN 9781429212427. Jump up ^ Johnson, Leonard R., ed. ( 2003 ). Essential medical physiology ( 3rd ed. ). Amsterdam : Elsevier Academic Press. ISBN 9780123875846. Jump up ^ Heinemann, Henry O. ; Goldring, Roberta M. `` Bicarbonate and the regulation of ventilation ''. The American Journal of Medicine. 57 ( 3 ) : 361 -- 370. doi : 10.1016 / 0002 - 9343 ( 74 ) 90131 - 4. Jump up ^ Koeppen, Bruce M. ( 2009 - 12 - 01 ). `` The kidney and acid - base regulation ''. Advances in Physiology Education. 33 ( 4 ) : 275 -- 281. ISSN 1043 - 4046. PMID 19948674. doi : 10.1152 / advan. 00054.2009. ^ Jump up to : page 556, section `` Estimating plasma pH '' in : Bray, John J. ( 1999 ). Lecture notes on human physiology. Malden, Mass. : Blackwell Science. ISBN 978 - 0 - 86542 - 775 - 4. Jump up ^ Kamens, Donald R. ; Wears, Robert L. ; Trimble, Cleve ( 1979 - 11 - 01 ). `` Circumventing the Henderson - Hasselbalch equation ''. Journal of the American College of Emergency Physicians. 8 ( 11 ) : 462 -- 466. doi : 10.1016 / S0361 - 1124 ( 79 ) 80061 - 1. Jump up ^ Hogan, DL ; Rapier, RC ; Dreilinger, A ; Koss, MA ; Basuk, PM ; Weinstein, WM ; Nyberg, LM ; Isenberg, JI. `` Duodenal bicarbonate secretion : Eradication of Helicobacter pylori and duodenal structure and function in humans ''. Gastroenterology. 110 ( 3 ) : 705 -- 716. doi : 10.1053 / gast. 1996. v110. pm8608879. External links Physiology : 7 / 7ch12 / 7ch12p17 - Essentials of Human Physiology Physiology of the kidneys and acid - base physiology Renal function Secretion clearance Pharmacokinetics Clearance of medications Urine flow rate Reabsorption Solvent drag sodium chloride urea glucose oligopeptides protein Renal function Glomerular filtration rate Creatinine clearance Renal clearance ratio Urea reduction ratio Kt / V Standardized Kt / V Measures of dialysis Hemodialysis product PAH clearance ( Effective renal plasma flow Extraction ratio ) Filtration Renal blood flow Ultrafiltration Countercurrent exchange Filtration fraction Hormones Antidiuretic hormone Aldosterone Atrial natriuretic peptide Renin Erythropoietin Calcitriol Prostaglandins Acid - base balance Fluid balance Darrow Yannet diagram Body water : Intracellular fluid / Cytosol Extracellular fluid ( Interstitial fluid Plasma Transcellular fluid ) Base excess Davenport diagram Anion gap Arterial blood gas Winter 's formula Buffering Bicarbonate buffer system Respiratory compensation Renal compensation Other Fractional sodium excretion BUN - to - creatinine ratio Tubuloglomerular feedback Natriuresis Urine Retrieved from `` https://en.wikipedia.org/w/index.php?title=Bicarbonate_buffer_system&oldid=779077866 '' Categories : Electrolyte disturbances Buffers Talk Contents About Wikipedia Deutsch Polski Türkçe Українська Edit links This page was last edited on 6 May 2017, at 22 : 33. 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Question: what is the main buffer system in human blood
Answer: bicarbonate buffer system