Renal regulation of H+ Flashcards
What is the normal pH range of ECF
7.35-7.45
Why is body pH control so important
protein function is dependent on pH
How is pH of a solution determined
By the hydrogen ion concentration in the solution
Is ICF more or less acidic than ECF
ICF is more acidic as its normal pH is around 7.2
What are chemical buffers
Chemicals that bind to H+ and remove it from the solution if it’s acidic or release H+ into the solution if basic
What is the protein buffer system
Amino acids bind to H+
What is the Bicarbonate buffer system
CO2 + H20 can become H2CO3 ( carbonic acid ) which can H + HCO3 ( bicarbonate ).
And vice versa
List the two chemical buffer systems in the body
Protein buffer system and Bicarbonate buffer system
How do physiological systems stabilize pH via the renal system
using acids or bases
How do physiological systems stabilize pH via the respiratory system
using volatile acids including CO2. excess H+ will cause lungs to expel a lot of CO2 as H+ is converted to CO2
Compare the Renal vs Respiratory buffering methods
Renal : greater buffering capacity but effect takes several hours or a day
Respiratory : can only excrete volatile acids but effect happens within minutes
What happens if one of the buffering systems breaks down
The other system will compensate but it is not ideal
Where are the two physiological buffering systems in the body
The renal and respiratory system
Describe the normal control of pH mechanism in the renal system ( Hint: 6 steps )
1- HCO3 & H+ are filtered at the glomerulus
2- HCO3 in filtrate combines with H+ to make H2CO3
3- dissociates into H20 and CO2 both then diffuse into tubular cells
4- H2O and CO2 recombine into H2CO3 and then dissociate into HCO3 and H+ in the tubular cells
5- HCO3 is diffused into the blood and H+ is secreted into the filtrate
6- H+ combines with more HCO3 in the filtrate and cycle starts again
Where is 85% of the HCO3 filtered
PCT
Where is 10% of HCO3 filtered
DCT
Where is 5% of HCO3 filtered
Collecting Ducts
Is any of HCO3 excreted and explain why or why not
None of the HCO3 is excreted. The purpose of filtration is to get rid of some of the H+ but the HCO3 should be kept in the body
What happens to H+ in the nephron
It is constantly being reabsorbed and then secreted again. most gets secreted again and that’s why urine is acidic
What is the normal pH is secretion of H+ is higher than reabsorption
Urine pH is between 4.5 - 7.4
Describe the renal correction of acidosis ( pH < 7.35 )
1- Excess H+ in filtrate
2- all available HCO3 combines with H+
3- Excess CO2 in filtrate will be reabsorbed
4- H20 and CO2 recombine to make H2CO3 that dissociates into HCO3 and H+ in the tubular cells
5- HCO3 diffuses into blood to increase pH and H+ excreted into filtrate
6- no more HCO3 so excess H+ will be excreted into urine , cycle won’t start again as normal
How is H+ buffered in the urine
PH below 4.5 will stop H+ secretion and limit reabsorption of HCO3
1- NH3 will be secreted by tubular cells into the filtrate
2- H+ will combine with NH3 to make NH4+
3- NH4+ can’t be reabsorbed so H+ will be excrete in urine
What is the physiological effect of a drop in PH
1- effects binding of calcium to plasma protein since H+ binding to albumin then there will be more free calcium ions
2- Calcium ions block sodium channels and reduces their opening
3- AP firing in myocytes and nerves is reduced
4- membrane potential of excitable cells will stabilize and they’ll be harder to stimulate
What conditions can result from a drop in Ph ( Hint: 3 )
1- Cardiovascular depression : bradycardia followed by asystole
2- CNS depression : stupor followed by coma
3- reduced muscle contraction
