Acid - base balance Flashcards
Normal plasma [H+]
40 nM
Sulfur containing amino acids
Cysteine, methionine
What amino acids make HCl?
Lysine, arginine and histidine
The bicarbonate system
H+ + HCO3 - = CO2 + H2O
The phosphate system
H+ +HPO4 2- = H2PO4 -
The protein buffers
H+ + Pr- = HPr
What is a buffer?
It is a solution that minimizes the change in [H+].
What ratio is important in the bicarbonate buffer system?
Plasma [CO2]
Is proportional to the partial pressure of CO2 in plasma
How do you measure pH?
Arterial Blood Gas (ABG)
What does pK represent?
The Equilibrium constant of the reaction
When do Buffers resist change?
[Base] = [acid]
When are Buffers the most effective?
When 1 pH is on either side of pK.
What controls PCO2?
Alveolar ventillation
What controls the [HCO3-] ECF ?
Independent regulation
How kidneys control acid-base levels?
By excretion of an acidic or basic urine
What are the primary renal mechanisms involved in regulating acid and base levels?
“Reabsorption” and secretion of HCO3 -
Formation of new HCO3-
Secretion of [H+] into tubular fluid
Buffer system within tubule that react with secreted [H+]
What are the 3 ratios important for buffering?
NH3:NH4+ HPO4 2-:H2PO4- HCO3-:H2CO3
What does Carbonic anhydrase do?
Convert H2CO3 to make CO2 and H2O
Where does HCO3- get absorbed?
85-90% is absorbed in the proximal tubule. Also, a good place to secrete [H+]
What happens in the distal tubule and collecting duct in the bicarbonate system?
H+-ATPase pump more important in this part of nephron
In distal part of nephron [HCO3-] is low and H+ react with other buffers
Role of the Respiratory system
Chemosensitive area in medulla regulates respiration
Monitors [H+] of plasma via CSF indirectly
Charged ions can’t cross Blood brain barrier but CO2
Metabolic acidosis
Increase ECF [H+] or decrease ECF [HCO3-]
What causes metabolic acidosis?
Severe sepsis or shock = Lactic acid
Uncontrolled diabetes - overproduction of 3-OH-butyric aid & other ketoacids
Diarrhea = loss of HCO3- from GI tract
Metabolic alkalosis
High pH caused by Increase ECF [HCO3-] or decrease [H+]
What causes Metabolic alkalosis?
Excessive diuretic (thiazide0 use = chronic loss of Cl-, Na+ &K+ = increases H+ secretion
Vomiting = loss of H+ from GI tract
Ingestion of alkaline antacids
Hypokalemia
What are the 3 mechanisms that change pH?
Intra- and extra- cellular buffering
Respiratory adjustment of ECF PCO2
Renal adjustment of ECF [HCO3-]
Acidosis
Plasma pH <7.4
Alkalosis
Plasma pH >7.4
How do you produce the NH3?
Glutamine with the enzyme glutaminase
Phosphate system carried on
Further H+ secreted into Lumen buffered by HPO4 2-
Very effective buffer because pK=6.8 (close to pH of filtrate)
