Costanzo Renal Pysiology: Acid-Base balance Flashcards
What are the two kinds of acids produced by the human body?
(1) volatile acids (CO2)
2) Non-volatile acids (fixed acids eg sulfuric or phophoric acid
What is carbonic anhydrase?
An enzyme that converts CO2 and H2O to HCO3- H+
What is the major extracellular buffer and what is its pKa?
HCO3- is the major extracellular buffer with a pK of 6.1.
What is the most important urinary buffer?
Phosphate is the most important urinary buffer with pK of 6.8.
What are some major intracellular buffer?
(1) organic phosphates (ADP, ATP, 2,3-DPG, etc)
(2) imidazole and amino groups on proteins
(3) Hemaglobin
Is hemaglobin a better buffer when its oxygenated or non-oxygenated?
Non-oxygenated hemoglobin is a better buffer
What is the Henderson Hasselbach equation?
pH = pKa + Log( [A-] / [HA] )
Where in the nephron is HCO3- primarily reabsorbed?
HCO3- is primarily reabsorbed in the proximal tubule.
What happens to HCO3 in alkalosis?
There is too much filtered HCO3- to be reabsorbed therefore HCO3- is excreted in the urine. Additionally, there is lower H+ concentration. This will decrease HCO3- reabsorption because H+ is required for the reabsorption of HCO3- .
What happens to filtered HCO3- if there is an increase in Pco2?
An increase in Pco2 (respiratory acidosis) will result in an increase in H+ ions which will after being secreted into the lumen, facilitate the reabsorption of HCO3-.
What happens to filtered HCO3- if there is a decrease in Pco2?
A decrease in Pco2 (respiratory alkalosis) will result in less H+ available for secretion and therefore there will be less HCO3- taken up from the tubules.
What is the effect of ECF volume expansion on HCO3- reabsorption?
HCO3- reabsorption is decreased by ECF volume expansion.
What is the effect of ECF volume contraction on HCO3- reabsorption?
HCO3- reabsorption is increased when there is ECF volume contraction.
What is the effect of angiotensin II on HCO3- reabsorption?
Angiotensin II often released secondary to volume contraction will increase the Na+/H+ exchange thus increasing HCO3- reabsorption.
What two methods are used to excrete fixed H+?
(1) titratable acids
(2) NH4+
How is H+ excreted as a titratable acid?
A portion of the H+ that is secreted binds with HCO3- to be converted back to CO2 and water to be reabsorbed. However, the excess H+ binds with filtered HPO4– to form
H2PO4- which is not reabsobed but excreted. This proressively lowers urine’s pH.
What is the minimum urinary pH?
4.4 is the minimum urinary pH.
What determines the amount of H+ excreted?
The amount and pK of the urinary buffer.
How is NH3 used to excrete H+?
NH3 diffuses into the acidic environment of the tubule. In the lumen NH3 binds with H+ to make NH4+ which is not reabsorbed but excreted.
How is potassium related to NH3 synthesis?
(1) hyperkalemia inhibits NH3 synthesis
(2) Hypokalemia stimulates NH3 synthesis.
What is metabolic acidosis?
Overproduction or ingestion of H+ leading to acidemia.
What happens to HCO3- during metabolic acidosis?
Arterial HCO3- decreases as it takes up extra H+
What is the respiratory compensation for metabolic acidosis?
hyperventilation (Kassmaul breathing) is the respiratory compensation for metabolic acidosis.
How is metabolic acidosis corrected?
(1) increased excretion of H+at titratable acid and NH4+
(3) increased reabsorption of HCO3- to bind up more H+
What adaptive changes occur in response to metabolic acidosis?
NH3 synthesis can be increased in metabolic acidosis.
What is the anion gap?
The unmeasured anions in the serum.
[Na+] - ( [Cl-] + [HCO3-] )
What is the normal anion gap?
12mEq/L
What is metabolic alkalosis?
the loss of H+(vomiting) through the loss of fixed H+ or increase in base.
What is the respiratory compensation for metabolic alkalosis?
Hypoventilation
How is metabolic alkalosis corrected?
By excretion of excess HCO3-
Why does vomiting exacerbate metabolic alkalosis?
Because the volume contraction leads to increased angiotensin II and aldosterone which leads to increased HCO3- reabsorption.
What causes respiratory acidosis?
A decrease in respiratory rate leading to an increase in retained CO2.
What is the renal compensation for respiratory acidosis?
increased H+ secretion leads to increased HCO3- reabsorption. There is also an increase is H+ excretion via titratable acids and NH4+
What is the difference between acute and chronic respiratory acidosis?
In acute respiratory acidosis renal compensation has not occured yet.
In chronic respiratory acidosis renal compensation has already begun.
