acid base cards Flashcards
bicarbonate concentration in:
plasma
interstitium
intracellular
24 mM plasma
28mM interstitial
10mM intracellular
Daily acid excretion rates
How are H+ ions transported into the tubular lumen?
How are they retained in the lumen?
~4.3 mEq of H+ is secreted per day and then reabsorbed after combining with bicarbonate in order to reabsorb the full 99.9/% of the bicarbonate that is filtered each day
an additional 80 mEq must be secreted to excrete the amount of H+ generated by non-volatile acid waste production (non-CO2 excretable)
In total ~4400 mEq of protons are secreted into the tubules per day
H+ is transported via the Na+/H+ lumenal exchanger.
They are retained by being bound to NH3 and creating impermeable NH4+ ions. ~ 50%
The rest are bound by Sodium phosphate ions to generate sodium phosphate salts.
What is the minimum pH of urine, at maximal H+ excretion?
minimum urine pH is 4.5
How do the tubules produce a Net Gain of HCO3- for the body?
How do the intercalated cells of the collecting tubules produce a net gain of 1 HCO3- for the body?
By excreting H+ ions bound to a buffer other than HCO3-.
ie. phosphate or urea.
as NaH2PO4 salt
or NH4+ as ammonium ions.
The intercalated cells produce H+ ions from CO2 and H20 via Carbonic anhydrase.
They then secrete H+ via luminal H+ ATPase pump, along with NH3 which diffuses passively into the lumen.
In the lumen NH4+ ions are generated, trapping the proton and NH4 ions in the lumen, which are excreted for a net gain of one bicarbonate.
What reaction can produce a Net Gain of 2 HCO3- for the body?
In the proximal tubules, glutamine can be broken down into 2HCO3- and 2 NH4+ ions.
The NH4+ ions are then pumped into the lumen by a NH4+/Na+
In the lumen the NH4+ combines with Cl- ions to form a salt and is excreted.
This system can be drastically increased if there is need and excess acid generation, and can excrete up to 500mEq/day of protons. .
How is net acid excretion calculated?
Net acid excretion = NH4+ excretion + Urinary titratable acid - HCO3- excretion.
Titratable acids include:
Phosphates mostly, then Creatinine, Sulfates, and Uric acid.
How does hypokalemia cause an increase in acid excretion?
Hypokalemia decreases the activity of Na/K pumps, elevating intracellular Na+ concentrations.
This inhibits the activity of the Na+/H+ antiporter in tubular cells, decreasing acid output.
What protein in the Renal tubular cells couples Na+ absorption and H+ excretion?
If a compound (ie Ang2) increases Na+ absorption, how does it affect H+ excretion?
The Na+/H+ Exchanger, the NHE protein
Things that increase Na+ absorption generally also increase H+ EXCRETION, and HCO3- absorption
Note, this protein can also exchange NH4+ ions for Na+ ions, and it does so in the Proximal tubule cells.
What are some causes of metabolic acidosis?
Renal damage, failure of renal H+ excretion or HCO3- resorption.
Excessive lactic acid formation
Excessive keto acid formation, diabetes mellitus
Ingestion of acids
Excessive loss of bases due to diarrhea or vomiting of intestinal/duodenal fluids
Renal failure or reduced GFR, causing reduced NH4+ and phosphate H+ excretion.
What are causes of metabolic ALKalosis?
Diuretic drugs, increase tubular flow and increase Na+ resorption, increasing H+ excretion
HyperAldosteronism,
Excessive aldosterone directly stimulates H+ ATPase pump from intercalated cells.
Also stimulates the Na/K pump, which increases Na+ absorption, increases activity of the Na+/H+ exchanger and increases H+ excretion.
Vomiting of only the stomach contents
Alkaline drug consumption like sodium bicarbonate for stomach ulcers.
What are treatments of metabolic acidosis and alkalosis?
Acidosis treatment: large amounts of oral sodium bicarbonate, and or injection of NaLactate or NaGluconate.
The Na+ will combine with bicarbonate to prevent its excretion and retain in blood
