Renal Regulation of H+ Flashcards
(28 cards)
What is the normal ECF PH range?
7.35-7.45
Why is it so important for PH to remain in range?
To ensure enzymes can work efficiently
Why is intracellular PH more acidic than ECF?
- high intracellular acid production 7.2
- cells have adapted to slightly lower PH through increased buffering capacity
What are the three types of buffer?
1) Chemical
2) Protein
3) Bicarbonate
What is a chemical buffer and where are they found?
- Substances that bind to H+ removing it from solution if higher concentration
- or release H+ if in low concentration
- Present in all body fluids, restores Ph within fraction of second
How does bicarbonate buffer?
Carbonic acid can either form CO2 and H20 (to be removed from body) to decrease acidity or H+ and HCO3- to increase acidity
What enzyme catalyses breakdown of carbonic acid to water and carbon dioxide?
carbonic anhydrase
What are the two systems used as physiological buffers and how do they differ?
1) Renal
- greater buffering capacity
- takes longer
2) Respiratory
- Can only excrete volatile acids but effects within minutes
Breakdown of one system can be compensated by the other
How does H+ in filtrate get into the tubular cells of the nephron?
- small excess of H+ in the filtrate at glomerulus along with HCO3-
- combine to form carbonic acid and then dissociate to form H2O and CO2
- These diffuse into tubular cells
What happens to the water and CO2 in the tubular cells?
- Combine to form carbonic acid > HCO3- and H+
- broken down originally to get the products into the tubular cells
- HCO3- can then be reabsorbed into the blood
- Hydrogen can be secreted back into the filtrate
- H+ can rebind with more HCO3- and cycle will start again
- Results in HCO3- reabsorbtion and H+ secretion
Where is HCO3- reabsorbed in the nephron?
- PCT 80%
- DCT 10%
- Collecting duct 5%
- Excrete almost no bicarbonate
Where is H+ reabsorbed then secreted in the nephron?
- PCT 85%
- DCT 10%
- Collecting duct 5%
- Reabsorbed and secreted in all locations
How do kidneys regulation of PH change to correct acidosis?
- May be excess CO2 in filtrate which diffuses into tubular cells at same time as CO2 which is product of carbonic acid
- HCO3- reabsorbed into blood as usual and starts to neutralise blood to return it to normal PH
- No more HCO3- is available to combine with the H+ when it re-enters the filtrate so is excreted in urine
- Get low urinary PH
How will regulation in the kidneys change with severe excess in hydrogen ions?
- Need a H+ concentration gradient to ensure movement back into filtrate after HCO3- released into blood
- If too many H+ ions still infiltrate no gradient
- so body secretes NH3 which diffuses into filtrate and combines with H+ to from NH4+
- NH4+ can’t move back into tubular cells as charged so must be excreted in urine
Where does ammonia used to regulate PH come from?
Protein metabolism
What problems are caused by acidosis?
- increase in free Ca2+ as albumin begins binding to H+, means more sodium channels can be blocked and reduction in AP firing of myocytes and nerves
- cells can longer be stimulated as resting membrane of cells is stabilised
What are the consequences of the free calcium?
- CV depression - bradycardia followed by a-systole
- CNS depression - stupor followed by coma
What are the causes of acidosis?
1) respiratory acidosis (CO2 causing acidosis)
- ventilatory failure
- severe ventilatory defects
What would you expect to see in the blood concentrations of respiratory acidosis?
- High CO2
- possibly low O2
- Low PH
- raised HCO3- due to compensation
What are the causes of metabolic acidosis (metabolic means as a result of kidney damage)?
- Renal injury/disease (less H+ & less HCO3- reabsorption)
- Aspirin overdose (induces hyperventilation
- diabetic ketoacidosis
- Alcoholism (damage due to inflammation, oxidative stress and hypertension)
- diarrhoea (Na+ lost in filtrate so less H+ secreted and less HCO3- reabsorbed)
- ## Addisons disease (hypoaldosteronism)
Why does Addison disease cause acidosis?
low aldosterone means less expression of the Na/H+ pump and so less H+ secretion and so less HCO3- reabsorption
What would you expect to see in blood chemistry for metabolic acidosis?
- Low PH
- Low ECF HCO3- concentration
- Normal O2 and CO2 except if have compensatory deep breathing to remove CO2
What PH is defined as alkalosis?
7.45
How is alkalosis corrected?
- Want either a decrease in H+ or increase in HCO3- in filtrate so less carbonic acid forms
- and less CO2 and H2O absorbed
- results in less H+ secretion and less HCO3- reabsorption
- HCO3- starts to be excreted as no H+ to combine with it
- HCO3- secretion and increase in H+ (as body continues to make it) will decrease PH
