Chapter 8 - Chapter 8 Regulation of Acid-Base Balance Acid-base balance is concerned with maintaining a normal H ion concentration in the body

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Chapter 8 Regulation of Acid-Base Balance Acid-base balance is concerned with maintaining a normal H + ion concentration in the body fluids. How is this balance achieved? - By utilization of buffers in both ECF and ICF Two mechanisms for buffering: - Respiratory mechanisms that excrete CO 2 - Renal mechanisms that reabsorb HCO 3 - (bicarbonate) and secrete H + (hydrogen ions) pH of Body Fluids The H+ concentration of the body fluids is extremely low. - Arterial blood: 40 nEq/L (40 x 10 -9 ) Because of low concentration, H + concentration is expressed as the negative logarithm, or pH: pH = - log 10 [H + ] The normal H+ concentration of 40 x 10 -9 Eq/L is converted to pH as follows: pH = - log 10 [40 x 10 -9 Eq/L] = 7.4 All cellular, tissue, and organ processes are sensitive to pH. Body fluid pH ranges from 6.8 to 7.8 - Life cannot exist outside of this range. The normal range of arterial pH is 7.32 to 7.42 - Essential for all cellular functions Acidemia: pH < 7.37 Alkalemia: pH > 7.42 Mechanisms that contribute to maintaining pH in the normal range include - Buffering of H + in both ECF and ICF – rapid, minutes - hours - Respiratory compensation - rapid, minutes - hours - Renal compensation – slower, hours – days
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The HCO 3 - Buffer System First, what is a buffer? A buffer is a mixture of a weak acid and its conjugate base or - a weak base and its conjugate acid HCO 3 - is an important buffer of the ECF. Plasma has a concentration of 23 to 25 mEq/L of HCO 3 - and a volume of 14L - can potentially buffer 350 mEq of H + Unlike the other buffer systems of the body (e.g., PO 4 3- ), the HCO 3 - buffer system is regulated by both the lungs and kidneys CO 2 + H 2 O H 2 CO 3 H + + HCO 3 - Carbonic anhydrase In alveoli (lungs) in epithelial cells of renal tubules The bicarbonate buffer system is the most powerful ECF buffer in the body. The two components of the buffer system are regulated: - HCO 3 - by the kidneys - O 2 by the lungs This regulation allows precise control of the pH of the ECF by - relative rate of removal and addition of HCO 3 - by kidneys - removal (rates of) of CO 2 by the lungs Acid: A substance that adds H + to body fluids Alkali: A substance that removes H + from body fluids
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Henderson-Hasselbalch Equation Used to quantitate the impact of changes in CO 2 and HCO 3 - on pH. pH = pK + log [HCO 3 - ] α P CO 2 pH = 6.1 + log [HCO 3 - ] 0.03 P CO 2 P C O 2 = partial pressure of CO 2 α = solubility of CO 2 At 37 ° C, solubility of CO 2 in plasma ( α ) = 0.03 pK = 6.1 K = equilibrium constant pK = - log 10 K (pH units) [HCO 3 - ] regulated by kidney PCO 2 in ECF: by rate of respiration If acid-base balance is disturbed because of a change in HCO 3 - , it is called metabolic acid-base disorder kidneys regulate plasma HCO 3 - Those resulting from a change in PCO 2 are termed respiratory acid-base disorder lungs control PCO 2 Metabolic production of Acid and Alkali
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This note was uploaded on 01/07/2012 for the course PHCH 6234 taught by Professor Farqui during the Winter '11 term at Palmer Chiropractic.

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Chapter 8 - Chapter 8 Regulation of Acid-Base Balance Acid-base balance is concerned with maintaining a normal H ion concentration in the body

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