Acid - Base Balance Flashcards
Regular Body pH
7.4
Acidosis
pH < 7.4
high hydrogen ion concentration
Alkalosis
pH > 7.4
low hydrogen ion concentration
change in pH resulting in death
a change of 0.6 in either direction can result in death
Normal Concentration of Hydrogen Ions
4x10^-8 eq/L or 4x10^5 meq/L
Body Buffers
- Intracellular Fluid
- Blood
- Interstitial Fluid
Intracellular Fluid as a Buffer
- Protein (non-exchangable)
- HPO4^2-
Blood as a Buffer
- Hemoglobin
- Protein (albumin)
- HCO3^-
Interstitial Fluid as a Buffer
- HCO3-
- HPO4^2- (Kidney)
- NH3 (Kidney)
Lines of Defense in an Acid Base Crisis
- Hemoglobin and Proteins
- HCO3^- buffer system (most important)
Protein Anion Buffer System
75% of the body’s buffering power
not physiologically significant
Protein Anion Buffer System Reactions
R-COOH <-> R-COO- + H+
R-NH2 + H+ <-> R-NH3+
Major ECF Buffer Systems
- Bicarbonate
- Phosphate
CO2/HCO3- Bicarbonate Buffer System
Most important ECF buffer
regulation from Lungs, Kidneys, Blood Buffer System
Bicarbonate Buffer System Reaction
CO2 + H2O + Enzyme <-> H2CO3 <-> H+ + HCO3-
Henderson-Hasselbach Equation for Bicarbonate Buffer System
pH= pK + log([HCO3-]/[H2CO3])
or pH = pK +log([HCO3-]/0.3PCO2)
pK = 6.1
Normal Ratio of HCO3 to H2CO3
20:1
Bicarbonate Buffer System
mixture of NaHCO3 and H2CO3
NaHCO3 can react with an acid to make H2CO2, H2CO3 can react with a base to make NaHCO3
Carbonic Anhydrase
enzyme that helps convert CO2 in blood to bicarbonate(HCO3) in the bicarbonate buffer system
When do buffers work best?
When pH is close numerically to pK
Why is the Bicarbonate Buffer system the most important buffer system?
- can be regulated by lungs and kidney (CO2&HCO3-)
- Erythrocytes are capable of “Chloride shift”
- Abundant supplies of Bicarbonate anion are available for buffering (HCO3-:H2CO3, 20:1)
Chloride Shift
- Chloride transported into the blood cell
- HCO3- buffer transport is favored out of the cell, into plasma
Phosphate Buffer System Reactions
HCl + Na2HPO4 <-> NaH2PO4 + NaCl
NaOh + NaH2PO4 <-> Na2HPO4 +H2O
Phosphate Buffer system
more active in the kidney tubule system than ECF
1/12 concentration in ECF compared to Bicarbonate Buffer System
tubular fluid has low pH that is closer to pK of the buffer
3 levels of pH regulation
- Bicarbonate Buffer System
- Respiratory System
- Renal Buffer System
Bicarbonate Buffer System in pH regulation
weak link, can become saturated
Respiratory System role in pH regulation
fast acting, within minutes,
Central Receptor and Peripheral Chemoreceptors
buffer power 2x greater than all chemical buffer systems
Respiratory System role in pH regulation
Central Receptor(Medulla Oblongata)
detects rise in [H+], causes increase in RR
Respiratory System role in pH regulation
Peripheral Chemorecptors
detects decrease in pH, pO2, increase in pCO2 causes increased RR
Respiratory System role in pH regulation
Flaw of Respiratory System in pH regulation
cannot stop breathing so it is less effective in an alkalotic crisis
Renal Buffer System
recruited after 3-5 hours if respiratory system fails to compensate
reabsorbs base while excreting acid
Works using secretion and reabsorbtion
Renal Buffer System
Secretion
secretes H+, leading to it being excreted
counter transport of Na+ and H+
secondary active transport,
Renal Buffer System
Reabsorbtion
reabsorbs HCO3-, prevents its excretion
HCO3- from the glomerular filtrate will combine with H+ to form H2CO3 which will then form CO2 + H2O
Renal Buffer System
In the Proximal Convoluted Tubule
for every Na+ reabsorbed
1. H+ secreted
2. HCO3- reabsorbed
3. H+ combines with HCO3- to form H2CO3
both K+ and H+ compete for cotransport with Na+
In the Distal Convoluted Tubule
- H+ is secreted
- K+ stays in the ECF
- H+ is buffered in the tubule by HPO4-2 and NH3
- NH4+ is the excretory form of H+
Normal pCO2 level
40 mmHg
respiratory proxy
pCO2 = H+ = acid
Normal HCO3- level
24 mEq/L
metabolism proxy
HCO3- = OH- = base
Metabolic Acidosis
acidic condition resulting from metabilism problem
Diabetic Ketoacidosis
Respiratory Acidosis
acidic condition resulting from an inability to maintain normal ventilation rate or move normal respiratory volumes
Chronic Emphysema, Asthma Attack
Metabolic Acidosis Signs
pH<7.4
HCO3-<24mEq/L
pCO2<40mmHg (increased ventilation rate)
HCO3- is the cause, pCO2 is the compensation
Respiratory Acidosis Signs
pH<7.4
pCO2>40mmHg (poor breathing)
HCO3->24mEq/L(secrete more H+, increase NaHCO3- in ECF)
pCO2 is the cause, HCO3- is the compensation
Metabolic Alkalosis
exsessive vomiting, poisoning, overingestion of antacids, toothpaste by kids
Respiratory Alkalosis
pulmonary hyperventilation, ascent to high altitude, person in Hysteria
breath into a brown paper bag
Metabolic Alkalosis Signs
pH>7.4
HCO3->24meq/L
pCO2>40mmHg (hypoventilate)
HCO3- is the cause, pCO2 is the compensation
Respiratory Alkalosis Signs
pH>7.4
pCO2<40mmHg (Hyperventilation)
HCO3-<24meq/L (increased secretion of HCO3- for excretion)
pCO2 is the cause, HCO3- is the compensation
Buffer Base
sum of all conjugate bases in 1 liter of systemic arterial blood
Buffer Base Example
[HCO3-] = 24mmol/L
[Protein] = 15mmol/L
[HHb/HbO2] = 9mmol/L
Total (Buffer Base) = 48mmol/L
Base Excess
change in concentration of Buffer Base from normal
Base Excess = Observed Buffer Base - Normal Buffer Base
Base Excess example
observed [HCO3-] = 16meq/l
normal [HCO3-] = 24meq/l
then
Base excess = 16meq/l - 24meq/l = -8meq/l
Base Excess in Metabolic Acidosis
< -5
Base Excess in Metabolic Alkalosis
> 5
Anion Gap
the difference in concentration between measured cations and anions in 1 liter of plasma
Sum of 2 cations - sum of 2 anions
Anion Gap in Metabolic Acidosis
[HCO3-] decreases in metabolic acidosis so the anion gap increases
Anion Gap in Metabolic Alkalosis
[HCO3-] increases in metabolic alkalosis so the anion gap decreases