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VCU PHIS 206 - Acid/Base Balance
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PHIS 206 1st EditionLecture 23Outline of Last Lecture I. RegulationII. If Ascending + Descending Not ParallelIII. Countercurrent ImportanceIV. HypothalamusV. BalanceVI. Normal Body FluidsVII. Regulation of H+ ConcentrationOutline of Current Lecture I. Hydrogen ConcentrationII. Dissociation of AcidsIII. Weak v. Strong AcidsIV. PhysiologyV. How to get rid of H+ in plasma?VI. PathologicalVII. How to Maintain Normal pHVIII. Chemical BuffersIX. Respiratory SystemX. RenalXI. Acidosis v. AlkalosisCurrent LectureI. Hydrogen Concentration-ph= -log[H+]-each log change is a 10-fold change in H+ concentrations-[H+] log[H+] pH10-6 -6 610-7 -7 710-8 -8 8-pH changes 1, then 10-fold change in H+ concentration-H+ goes up, pH goes downII. Dissociation of Acids-acid: adds H+ in solutionThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-[HA] [H+] + [A-]-equilibrium= k= [HA]/[H+][A-]-We can take –log[k]= pK NOTE: k=equilibrium constant-When pH=pK of acid, then acid is 50% dissociated and 50% associated-Graphical Representation10050 pKIII. Weak v. Strong Acids-strong acid: largely dissociated at low pH EX.) HCl pH=1-2 pK=small -weak acid: dissociated when at high pH EX.) acetic acid pH=3-4 pK=large-If neighborhood of pK, adding [H+] or removing [H+] will not make much of a difference-acids: adding or subtracting [H+] of solution has less effect when pH is near pK-every acid is called a buffer buffer: acid buffers’ effects of adding or removing [H+] 1. greatest when pH=pK (more buffering capacity)2. greatest when more concentrated acid (more buffering capacity)IV. Physiology-plasma pH: H+ concentration in plasma plasma pH=7.4o greater than 10-8 M; less than 10-7 M venous =7.3 arterial=7.45: more outgoing-plasma picks up carbon dioxide, so more acidic-increase CO2, increase H+, decrease pH-CO2 lost in pulmonary capillaries-Any plasma pH > 7.4 (ALKALOSIS)-Any plasma pH < 7.4 (ACIDOSIS)-Limits of plasma pH: from 7.0 to 7.8V. How to get rid of H+ in plasma?-major source of H+ = metabolism-H+ in diet EX.) orange juice, salad dressing-H+ when digesting food-We produce huge amounts of CO2, so increase in H+, and can cause alkalosis depresses neural activity %Dissociation pH cause coma hyperexcitabilityVI. Pathological-vomit: acidity of stomach lost, so negative H+ balance-diarrhea: losing alkaline solution; acidity left behindVII. How to Maintain Normal pH-3 Mechanisms to Maintain Constant Plasma pH1. Chemical buffers in plasma2. Respiratory system: blow off CO2, increase plasma pH, reduce acidity3. Renal: secrete H+ and control how much is secretedVIII. Chemical Buffers-Most important: carbonic acid buffer-CO2 + H2O H2CO3 HCO3- + H+-k=[ HCO3-] [H+]/ [CO2]-pK=6.1 (little buffering)-2nd major chemical buffer: proteins concentration low ranges above plasma pH and below plasma pH proteins only EXIST in plasma, not ICF-Hemoglobin: pK not close to pH-Phosphate buffer (great buffer b/c pK=close to plasma) problem: little phosphate in plasma-All good potential buffers, but conc. are low, so capacity is also lowIX. Respiratory System-can control rate of CO2 by controlling alveolar ventilation-has an enormous capacity of moving CO2 out-suspend respiration, then you double H+ in less than a minute b/c you CO2 is held in-bring system back to 7.4 bring to 7.1, 7.35, but never quite 7.4-respiratory system is IMPRECISEX. Renal-secrete H+ in urine rate of secretion is precisely related to plasma pH kidneys readjust imbalance of plasma pH-However, kidneys take hours to days to bring plasma pH to 7.4XI. Acidosis v. Alkalosis-Respiratory alkalosis: hyperventilate acidosis: snoring-Metabolic alkalosis: vomit acidosis:


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VCU PHIS 206 - Acid/Base Balance

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