Renal Regulation of Acid/Base Flashcards
What are some entries of acids/bases into body?
- De novo generation from metabolism
- activity of GI tract
- processing of ingested food
- tend to take in more acids, especially processed foods
- Metabolism of stored fat and glycogen
- kidneys
What is a buffer?
- Prevents large changes in pH after addition or loss of protons from external sources
- Not an infinite capacity- once used can’t buffer anymore
- All body fluids are buffers
What are some intracellular buffers?
Protein, phosphate, K/H exchanger
What is our main ECF buffer?
HCO3
CO2+H2O–> H2CO3–> HCO3 + H
Which compartment of fluid has largest buffering capacity?
ICF (more volume, bigger portion of fluid)
How does the K/H exchanger?
- Depending on concentrations, K and H switch places in order to maintain equilibirium
- facilitated diffusion
- If acidotic- H moves into cell, K out of cell
- If alkalotic- H moves out of cell, K into cell
The concentration of CO2 is essentially _____ and ____ on respiratory system
constant; respiratory
Bicarbonates role in acid base?
- made by kidney
- Freely filtered
- plasma 24 mmol/L, GFR 180 L/day= 4320 mmol/day filtered load
- essential that virutally all of filtered bicarbonate is reabsorbed
- don’t reabsorb bicarb if you’re alkalotic. Most of time, reabsorbing all bicarb
What is the renal handling of A/B?
- Proximal tubule- kidney reabsorb filtered load of bicarbonate (neutral)
- can also secrete organic bases/ or weak acids under appropraite condition
- Distal tuuble- kidneys secrete either protons or bicarb to balance net input
What are % of reabsorption of bicarb in diff segments?
85% proximal tubule
15% in loop henle/collecting duct (she’s calling it distal tubule)
What happens inside proximal tubule cell to achieve net zero movement in acid/base balance?
- Carbonic anydrase makes H and HCO3 inside cell
- H moves to apical side H-Na antiporter (H to apical, Na absorbed)
- Hco3 goes to basolateral side, reabsorbes with Na via Na-HCO3 symptoer or Cl-HCO3 antiporter
- Bicarbonate filtered from blood has disappeared
- Its place in the blood has been taken by the bicarb that was produced inside the cell
- No net change
- H ion is now water, so does not contribute to urinary excretion of H
- ON THE PICTURE IGNORE “BLOOD” IT’S WRONG!! THAT IS THE LUMEN OF THE NEPHRON!
What happens to HCO3 molecule in lumen?
Excreted (forms with H to turn into CO2 + H2O), but during process, we make additional HCO3 molecule to be absorbed into blood (replacing the molecule we lost)
What occurs in Type A intercalated cells in distal tubule?
- Apical membrane-
- H-k ATPase (H out to lumen, K into cell)
- H atpase (out to lumen)
- H out to lumen combines with HCO3 to make CO2+H2O
- Basolateral
- HCO3-Cl antiporter
- HCO3 into blood
- Cl into cell
- HCO3-Cl antiporter
Acid secretion is ____ process
active process
How do Type B intercalated cells contribute to acid/base balance?
- Secrete base, only works when we’re alkalotic
- Apical side
- HCO3-Cl antiporter (hco3 into lumen, absorb Cl)
- Basolateral
- H-K ATPase on apical
- H- ATPase on apical
What happens if we have too much base?
We excrete bicarbonate via type B intercalated cells
What happens if we have too much acid?
- Acid load will reduce amount of bicarb in blood
- kidney replaces lost bicarb by generating new bicarb
- H ions are secreted and combine with base of buffers other than bicab
- Other buffers such as phosphate bind with H
- this generates a new bicarb ion
What are titratable acids?
All the buffers that H can potentially bind to besides bicarb
- Only a finite amount of titratable acids
What is ammonium’s role in A/B balance?
- Limited amount of titratable acids
- the rest are excreted attached to ammonium
- catabolism of protein by liver generated CO2, water, urea, glutamine
What is glutamine?
- Created in liver after catabolism of protein
- taken up by proximal tubule
- glutamine is converted to bicarb and nh4
- NH4 is secreted into lumen of proximal tubule and bicarb exits into interstitium
- for every NH4 into urine, HCO3 goes into blood
What is general process a/b regulation in proximal tubule?
Reabsorbs bicard
produces ammonium
What happens with A/B Balance in loop of henle?
Reabsorb Bicarb in ascending loop
What happens with a/b balance in distal and CD?
Reabsorbs bicarb
secretes bicarb
What is equation for net acid excretion?
TA + NH4- HCO3
TA + NH4= excreted acids
Tells HCO3 gain/loss from body
What happens to NH4 and TA during acid load
- NH4 excretion goes way up
- TA excretion increases a little
- Net acid excretion goes up significantly
What happens to NH4 and TA, and HCO3 excretion levels in base load?
- Excrete higher amount HCO3
- Negative net acid secretion
- Little bit of NH4 excretion
Acidosis can result from either?
gain of acid or loss of bicarb
What causes acid gain? Base loss?
- Acid gain-
- decreased respiration- increased CO2
- keto acids- byproduct of naerobic metabolism, fuel source when glucose decreases
- renal failure- acid gain because kidney cannot remove acid from body
- Base loss
- diarrhea- normal reabsorb HCO3 in intestine with K, in diarrhea, moving too fast to reabsorb bases
What is the anion gap? What does it tell us?
- Sum of cation-sum of anions
- tell us if we have acid gain or base loss
- normal 8-12
- If acidotic, but AG is normal- means that you had loss of base
- If acidotic and AG >12- means you had gaine of acid
What situations in body would lead to alkalosis?
- Results from loss of fixed acid or gain of HCO3
- Loss of fixed acid
- hyperventilation
- vomiting
- Gain of HCO3
- bicarb overdose (tums)
- chronic diuretic usage
The concentration of metabolic acids and HCO3 is regulated by the
kidney
How does the anion gap not change when you have an acidosis?
- The lost bicarb is replaced by Cl- so anion gap does not change!
- This means you have a loss of base
What are the 2 processes that the kidneys regulate HCO3 concentrations?
- Reabsorption of filtered HCO3
- Gneration of new HCO3
