Basic of Acid Base Flashcards
Types of Acids
Volatile
Fixed
Organic
Endogenous:
- Respiration: H2CO3 (Volatile)
- Phospholipids: H3PO4 (Fixed)
- Anino Acids: H2SO4 (Fixed)
- Exercise: Lactic Acid (Organic)
- Diabetes: Acetoacetic acid (Organic)
Exogenous:
- Drugs: Acetylsalicylic acids
- Toxins:
– Methanol (formic acid)
– Ethylene Glycol (oxalic acid)
CO2 + H2O = H2CO3 = H(+) + HCO3(-)
Henderson-Hasselbach Equation
pH = pK + log (anion/acid)
pH = pK+ log (HCO3-/H2CO3)
HCO3- = 24mEq/L
H2CO3= 1.2 (pCO2 & solubility of CO2)
Normal (Base/Acid)=20/1
Control:
- Base: Renal
- Acid: Respiratory (lung)
Acid-Balance Disturbance
Ratio Shift to 16/1.2 then pH = 7.2
- Uncompensated Acidosis
Ration return to 20/1 (Value still abnormal)
- Compensation
Values return to normal (24/1.2)
- Correction
Uncompensated Acidosis
Ratio Shift to 16/1.2 then pH = 7.2
Compensation
Acid-Base disturbance
Ration return to 20/1 (Value still abnormal)
Correction
Acid Base Disturbance
Values return to normal (24/1.2)
Mechanism to Control Acid-Base
Minutes:
- Intracellular Buffering
- Extracellular Buffering
Minutes to Hours:
- Respiratory Compensation (related to acid)
Hours to Days:
- Renal Compensation
Intracellular Buffering
Protein: albumin, globulin
Phosphate (Occur quickly kidney and bones)
- Minutes
Extracellular Buffering
Bicarbonate
Ammonia
Proteins
- Minutes
Respiratory Compensation
Alter CO2 excretion
- Minutes to Hours
Renal Compensation
Generate HCO3-
Alter H+ secretion
Ammonium
- Hours to Days
Instantaneous Buffering System
Bicarbonate: H(+) + HCO3(-) = H2O + CO2
Hemoglobin: HHb = H(+) +Hb(-)
Phosphate: H2PO4 = H(+) + HPO4-
Plasma Protein: HPr = H(+) + Pr (-)
Ex. RNH3+ = RNH2 + H+
- pH=pK(RNH3) + log ((RNH2)/(RNH3+))
Hemoglobin
Buffer in Blood
- After releasing O2 to peripheral tissues => binds to CO2 and H+ (NH+)
– As blood reaches the lung it releases CO2 & H+
— H+ and HCO3- ions form carbonic acid
Where CO2 is found
23% wil be attached to Hemoglobin
7% dissolved in plasma
70% in Bicarbonate Ions
Respiration
Second line of defense 12 to 24 hr
- H2CO3 (carbonic acid) converted to CO2 and excreted by lungs
– Cannot exhale fixed acids
Effect of Ventilation on pH
When Ventilation Increase => pH increase with it
When Ventilation decrease => pH decrease with it
Effect of pH on Ventilation
When pH increase => Ventilation decrease with it
When pH decrease => Ventilation increase with it
pH and Ventilation
The goal is to stay consistent
- Venti Increase => pH Increase => Venti decrease => pH decrease => Venti Increase
– as you can see it’s just a cycle to keep everything in control
Renal Compensation
Nephrons cannot produce urine with pH < 4.5
Mechanism for Compensation:
1) Reabsorption of HCO3- (Bicarbonate)
2) Excretion of H+
3) Excretion of ammonium ions
Occurs over hours to days
Bicarbonate Buffering System
Proximal Tubules
- Na+/H+ Exchanger (Na reabsorbed with H secreted)
- Carbonic anhydrase
- Na+/K+ ATPase and HCO3- Exchanger
- 85% HCO3- Reabsorption
- High capacity, low gradient system H+ secretion (Can’t change pH much)
- Achieve urine pH = 6.7-7.0
Bicarbonate Buffering System
Distal Tubule/Collecting Ducts
- H ATPase
- Carbonic Anhydrase (I Cells)
- Cl-/HCO3- Exchanger
- 5%-10% HCO3- reabsorption
- Low capacity, high gradient system for H+ secretion
- Achieve urine pH = 4.5
– Main determinant of urinary pH
Proximal Tubules
Bicarbonate Buffering
Apical membranes of tubules are IMPERMEABLE to HCO3- (bicarbonate)
- Carbonic anhydrase catalyzes formation of H2CO3 from H2O and CO2 (use bicarbonate CO2)
– As CO2 increases in filtrate, CO2 diffuses into tubule cells and form H2CO3
—H2CO3 dissociate to HCO3- and H+
H+ secretion. HCO3- & Na+ reasorption (NBCe1)
Distal Tubule & Ducts
Bicarbonate Buffering
Type A Intercalated Cells
- CO2 + H2O with CAll => H2CO3
- H2CO3 => HCO3- + H+
– The H+ will get secreted with the help of an ATP
– HCO3- will get reabsorbed through AE1 ( Exchanger with HCO3-/CI-)
Ammonium/Ammonia Buffering
Proximal Tubule Cells
Cleaves Glutamine in the Proximal Tubule Cells
Glu => 2NH4+ and 2HCO3-
2NH4+
- 2 NH4+ => NH4+
– Get secreted (in an exchanger with Na+)
— Binded by CI- lumen and get excreted
2 HCO3-
- 2HCO3- => 3HCO3-
– Gets reabsorbed with Na+ in a symport channel
Production and secretion of NH4+ (ammonium) in proximal tubule, thick ascending loop and distal tublule
