A P Exam 4 Study Guide Lecture 1 Acid Base Balance pH Levels pH the measure of acidity in a solution relative H concentration in body fluids o Greater H acidic o Lower H alkaline o H are by products of metabolism either from lactate or ketone bodies All functional proteins are influenced by H therefore almost all reactions are influenced by pH of their fluid environment pH Balance in Body Fluids o Arterial blood 7 4 o Venous blood and Interstitial fluid 7 35 o Intracellular fluid 7 0 neutral pH rises lower H pH falls higher H o arterial pH 7 35 acidosis o arterial pH 7 45 alkalosis Lower pH more acidic metabolites and CO2 Acid Base Classification individually HCl Strong Acid SA dissociates completely which releases all of its H Weak Acid WA only dissociates partly H2CO3 Strong Base SB dissociates easily and accepts H Hydroxides OH Weak Base WB bicarbonate ammonia Chemical buffer system a system of one or more compounds that acts to resist changes in pH when a strong acid or base is added OVERVIEW 1 Chemical Buffer Systems 1st line of defense Act within a fraction of a second to attempt resisting changes in pH Muscle Carnosine Only temporary 2 Brain Respiratory System Act within 1 3 minutes to counteract acidosis or alkalosis Respiratory Buffer 3 Renal System Kidneys Require hours or even a day to react to changes in blood pH Only kidneys can remove excess metabolic acids from body 3 chemical buffer systems a change in H in 1 fluid compartment is compensated by a shift in another compartment if 2 or more compounds Bicarbonate Buffer System ONLY important buffer in extracellular fluid ECF o Substances H2CO3 Carbonic Acid WA NaHCO3 Sodium Bicarbonate WB HCl Hydrochloric Acid SA NaOH Sodium Hydroxide SB o Based off equilibrium H2CO3 HCO3 o Resists a large decrease in pH when acidic substances are added to a H This is because only small amount of H remain as free ions the rest bind to HCO3 to form carbonic acid o Resists a large increase in pH when basic substances are added to a solution solution This is because most of the H2CO3 forms HCO3 and H when H is removed o Responds quickly to addition of carbon dioxide and lactic acid from exercise ketone bodies and fatty acids from an elevated fat metabolism and large amounts of NaHCO3 from antacids Phosphate Buffer System very effective buffer in urine and intracellular fluid ICF o Substances NaH2PO4 Sodium dihydrogen phosphate WA NaHPO4 Sodium monohydrogen phosphate WB o Similar mechanisms to bicarbonate system o Phosphate containing molecules such as DNA RNA ATP and phosphate o Two main ions fluctuate between gaining and losing H ions to help When pH decreases ions likes HPO4 bind H to form H2PO4 ions act as buffers balance pH raising pH When pH increases H2PO4 releases H into solution lowering pH Protein Buffer System 3 4 of buffering power of all bodily fluids is in the cells o Substances Intracellular proteins hemoglobin histone proteins nucleic acids Plasma proteins o Capacity to act as buffers is due to functional groups of amino acids COOH and NH2 being able to act as acids and bases As H increases pH drops more H binds to NH2 to form As H decreases pH raises COOH is a SA which releases H NH3 raising pH lowering pH o Amphoteric Molecules a single protein that can act as an acid or base depending on the pH of its environment o Hemoglobin example Hb is negatively charged after releasing O2 which causes rapid binding of H from carbonic acid dissociation to Hb causing minimal pH changes Respiratory Buffer System influenced and achieved by bicarbonate buffer system Acts more slowly than chemical buffers BUT has 2x buffering capacity of all Decreases in body fluid pH stimulate neurons in the brainstem to cause the rate chemical buffer systems combined and depth of ventilation to increase o Increased ventilation allows CO2 to be expelled from the lungs at a greater rate decreasing body fluid CO2 levels o As CO2 level declines bicarbonate buffer system reacts o H binds to HCO3 o H concentration decreases pH rises to form H2CO3 which then forms CO2 and H2O Increases in body fluid pH inhibit neurons in the brainstem and cause the depth and rate of ventilation to decrease o Decreased ventilation allows less CO2 to be eliminated through lungs o CO2 levels increase because it is continually a by product of metabolism in all tissues o H2CO3 levels increase and dissociate to H and HCO3 o H concentration increases pH lowers SUMMARY o As CO2 levels increases pH decreases o As CO2 levels decrease pH increases o Hypoventilation respiratory acidosis increases blood CO2 levels o Hyperventilation respiratory alkalosis decreases blood CO2 levels Hypercapnia drop in CSF pH activates medulla chemoreceptors which increase respiratory rate and cause decreased CO2 levels which increases pH Respiratory Compensations o Metabolic acidosis increased respiratory rate and depth o Metabolic alkalosis decreased respiratory rate and depth CO2 H2O H2CO3 H HCO3 Acidosis hydrogen ions are increased and pH and bicarbonate ions are Alkalosis bicarbonate ion are increased and the concentration of hydrogen Both acidosis and alkalosis can be of two different types respiratory and decreased ions are decreased metabolic o Respiratory caused by various malfunctions of the lungs o Metabolic caused by various metabolic disorders which result in an excessive build up or loss of acids or bases Renal Buffer System directly regulates acid balance by altering the rate of H concentration and HCO3 reabsorption Secretion of H into the filtrate and the reabsorption of HCO3 into ECF cause extracellular pH to raise o Carbonic acid dissociates to form H and HCO3 o Antiport mechanism moves H into nephron lumen and Na into nephron cell o Na and HCO3 diffuse into ECF HCO3 in filtrate are reabsorbed o HCO3 combine with excess H in ECF to form carbonic acid increases extracellular pH o Some H that was secreted into filtrate combines with HCO3 which got into the filtrate through a filtration membrane in the form of NaHCO3 bicarbonate to form carbonic acid o Which then dissociates into CO2 and H2O o CO2 diffuses into nephron cells and forms carbonic acid which then dissociates to form HCO3 and H o HCO3 diffuse into ECF and H is secreted into filtrate Rate of H secretion increases as body fluid pH decreases or as aldosterone levels increase and the rate of secretion decreases when pH of body fluids increases Secretion of H is inhibited when urine pH falls below 4 5 o NH3 HPO4 2 and bicarbonate
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