1. Regulation of [H + ] Acid-Base Physiology.

2. pH vs [H + ]

4. Why is it important to regulate [H + ]?

5. H 2 O  H + + OH - Because of covalent bonding between O 2 and H, water has little tendency to dissociate the reaction is always far to the left. At equilibrium the concentrations of H + and OH - are very small.

6. Electrical Neutrality Essential to understanding A-B physiology. In a solution at equilibrium, Σ of + charges always equal to Σ of – charges. [H + ] = [OH - ] [H + ]+[Na + ] = [OH - ]+[Cl - ]

7. Strong Ions NaCl is a strong electrolyte. NaCl  Na + + Cl - In solution we have Na + and Cl - but no NaCl.

8. Strong Ion Difference (SID). The sum of all positive strong ions minus the sum of all negative strong ions. SID = (Σ + ions) - (Σ - ions). SID = ([Na + ]+[K + ]+[Ca ++ ]) - ([Cl - ]+[Lact - ])

9. Negative SID  acid Positive SID  alkaline

10. Strong Ions and Carbon Dioxide Adding CO 2 to a solution with a positive [SID] has a dramatic effect on [H + ]. CO 2 + H 2 O H 2 CO 3 HCO 3 - + H+ CO 2 pushes this equation to the right and therefore increases [H + ] which decreases pH.

11. How does the body regulate [H + ]? By controlling the independent variables. Respiratory system controls P CO2. Renal system controls SID, mostly by controlling [Cl - ]. Slight disturbances in pH can have serious consequences.

12. Buffers Buffers resist changes in pH by converting strong acids or bases to weak ones

14. Physiologic Buffers Body systems that control output of acids, bases, or CO 2 and thus stabilize pH Respiratory System HCO 3 - + H+ H 2 CO 3 CO 2 (expired) + H 2 O Urinary/Excretory System (can regulate H+ secretion into urine)

15. Buffer Systems = Chemical Buffers Systems that quickly bind or release hydrogen ions

16. Bicarbonate Buffer System CO 2 + H 2 O H 2 CO 3 HCO 3 - + H+ Carbonic Acid is a weak acid Enzymes work best at pH of 6.1 Reaction to right lowers pH Reaction to left raises pH

18. Phosphate Buffer System H 2 PO 4 - HPO 4 2- + H+ Reaction to right lowers pH Reaction to left raises pH Enzymes work ideally at pH of 6.8

19. Protein Buffer System – most common buffer system Carboxyl groups on amino acids --COOH --> --COO- + H+ Here it is acting like an acid as a proton donor Amino groups on amino acids --NH2 + H+ --> --NH3+ Here it is acting like a base, a proton acceptor