Acid - Base Balance:

Acid - Base Balance
HA <===> H⁺ + A^-

K_eq =      [H⁺] + [A^-]
                   [HA]

Plasma Bicarbonate
[HCO₃^-]_plasma = 23 mEq/L

Changes indicate renal or respiratory problems

CO₂ + H₂O <----> HCO₃^- + H⁺

OPEN BUFFER SYSTEM!

Henderson-Hasselbalch  Equation

[H⁺]  =  K_eq  x  [HA]
                          [A-]

-log [H⁺] = -log K_eq + log  [A-]
                                            [HA]

pH   =  pK_a + log [A-]
                            [HA]

pK_a
• when pH = pK, acid is 50% dissociated
• when pH = pK, 50% of buffer is in each form giving maximum buffering capacity
• match pK of potential buffers to desired pH

Metabolism
• Constant source of H⁺ and thus reduces plasma pH
• Proteins --> H₂SO₄ , HCl, H₃PO₄
• Fats --> ketone bodies such as acetone &  hydroxybutyric acid
• Oxidation ---> H⁺ from CO₂

Acid - Base Balance:  Fig 18.23

Plasma Buffers
• H₂CO₃
• H₃PO₄ and organic phosphates
• Proteins at ionized ‘R’ groups

Acid - Base Balance: Respiratory Mechanisms:  Fig 18.24

PCT: HCO₃^- & H⁺  Fig 18.25
DCT: HCO₃^- & H⁺ : Fig 18.26
Glutamine: NH₄⁺ ,  HCO₃^- & H⁺ : Fig 18.27