Acid-Base Balance Flashcards
ECF acidosis leads to what changes in K?
Hyperkalemia and decreased renal K excretion due to inhibition of ROMK
ECF alkalosis leads to what changes in K
Hypokalemia and increase renal K excretion due to activation of ROMK
What is a buffer?
A substance that preserves the original H-ion concentration when adding acids or bases. Offsets the reaction
What are some buffers in the maintenance of acid- base homeostasis?
- Intra and extracellular buffers
- Regulation of breathing
- Long term by the kidneys
Where is a buffer most effective?
Within 1 pH unit of its pKa
What are some non-HCO3 buffers?
- hemoglobin
- organic phosphates
- inorganic phosphates
- plasma proteins
- intracellular proteins
What ratio determines pH?
HCO3 to CO2
Why are we able to buffer with a buffers whose pKa is so much lower than physiological pH?
It is an open system and ventilation adjusts to maintain pCO2
What happens in respiratory acidosis?
CO2 and HCO3 increase. Acid is secreted and HCO3 is reabsorbed
What happens in respiratory alkalosis?
Low on CO2 and HCO3 and the kidneys will secrete HCO3 and Cl - retention
What is the effect of metabolic acidosis?
Acid is built up ie lactic acid build up and results in hyperventilation
What is the effect of metabolic alkalosis?
Loss of acid which leads to hypoventilation
What compensatory mechanism for acid/base load rakes the least amount of time?
ECF distribution
What compensatory mechanism for acid/base load rakes the most amount of time?
Acid secretion. Have to turn on alpha intercalated cells
How are strong acids eliminated?
The pKa of these is below urine pH so they remain dissociated and cannot be excreted in the acid form so have to use NH4 trapping
How is ammonium generated in the PT?
Ammonia is made by the breakdown of gultamine. It is secreted into the lumen and equilibrates with NH4 and NH3 because the pH is below the pKa
How is HCO3 absorbed in the proximal tubular reabsorption?
HCO3 in the lumen is converted into CO2 by CA. This can now diffuse into the cell and is converted back into HCO3 with H2O. The hydrogen ion gets pumped back into the lumen while HCO3 enters the blood through Na HCO3 cotransporters
How is new HCO3 generated in the PT?
CO2 from the blood diffuses into the cell and with water gets converted to HCO3 and a hydrogen ion. The hydrogen ion is pumped into the lumen and HCO3 is pumped out through NaHCO2 pump into the blood
What happens the the H ions that get put into the lumen at the PT?
These are buffered by weak acids conjugate base. Usually phosphate
How is HCO3 created in the CD?
Co2 from the blood filters in alpha intercalated cells and is converted to HCO3 and pumped back in the blood with a HCO3/Cl pump and the H ion is pumped into the lumen and combines with a conjugate base of a weak acid
What is the pH of urine as it leaves?
around 4.4
How are strong acids excreted in the urine?
Because their pKa is below that of urine, they remain dissociated and are trapped in the lumen by combining with ammonia
How is ammonia/ammonium produced in the PT?
Breakdown of glutamine
Describe the process of NH4 trapping?
Ammonium is formed in the PT and travels in the loop of Henle until it reaches the TALH where it is reabsorbed in the interstitium by NKCC. Here it equilibrates to the NH4 and NH3 form. NH3 is able to cross into the CD and trap H ions and is unable to leave. Thus lowering pH
