SM 201/202 Acid Base Integration Flashcards
Which organ mediates removal of volatile acids in acid-base balance?
The lungs, because they expire the volatile acid: CO2
Which organ mediates removal of non-volatile acids in acid-base balance?
The kidneys, because they excrete non-volatile acids: like the titratable acids, ammonia
Does the gut make more acid or base per day?
The gut makes more acid, which must be excreted by the kidneys
What organ gives rise to metabolic acid-base disorders and what organ compensates for them?
Metabolic acid-base orders are caused by the Kidneys and rapidly compensated for by the Lungs
What organ gives rise to respiratory acid-base disorders and what organ compensates for them?
Respiratory acid-base orders are caused by the Lungs and slowly compensated for by the Kidneys
How quickly are respiratory acid-base disorders compensated?
Slowly, because the kidneys take days
How quickly are metabolic acid-base disorders compensated?
Rapidly, because the lungs change breathing rate quickly
What are the 4 defenses against acid/base changes?
Extracellular buffering (immediate) Respiratory compensation (minutes) Intracellular buffers (hours) Renal excretion (4-6 days)
How long does it take for Extracellular Buffering to fix acid/base changes?
Extracellular buffering by HCO3 occurs immediately
How long does it take for Respiratory Compensation to fix acid/base changes?
Respiratory Compensation by hyperventilation and hypoventilation occurs in minutes
How long does it take Intracellular Buffers to fix acid/base changes?
Intracellular Buffers like proteins and organic phosphate occurs in hours
How long does it take for Renal Excretion to fix acid/base changes?
Renal Excretion takes 4-6 days
What is used for fine tuning of acid/base disorders?
Fine tuning occurs via renal excretion of acid and base
What are the major intracellular buffers?
Histidine, HCO3, Phosphate
Is HCO3 primarily an intracellular or extracellular buffer?
HCO3 is primarily an extracellular buffer, but there is some inside cells as well
Is intracellular pH lower or higher than extracellular pH?
Intracellular pH = 7.1 - 7.3 < Extracellular/Plasma pH = 7.4
How is the intracellular pH regulated?
Acid-base transporters on the cell membrane protect the cell against changes in pH
What transporters are found on cell membranes to regulate intracellular pH?
Na/H antiporter
Na-dependent Cl/HCO3 Exchanger
Na-independent Cl/HCO3 Exchanger
Are Cl/HCO3 exchangers on the cell membrane Na dependent or independent?
Both
Which cell membrane transporter protects against intracellular acidosis?
Na/H antiporter
Which cell membrane transporter protects against intracellular alkalosis?
HCO3/Cl antiporters (Na dependent and independent)
What does the graph of pH vs time look like in response to an acid or base load on a cell?
In an acid load, the graph sharply dips and then rapidly recovers due to the Na/H antiporter
In a base load, the graph sharply spikes and then rapidly recovers due to the HCO3/Cl antiporters
Do the kidneys excrete acid or base?
The kidneys can excrete either, but in the context of a protein heavy Western diet that makes lots of acid, the kidney will primarily excrete acid
Describe the relative contributions of different portions of the nephron for bicarbonate reabsorption?
All bicarb is filtered at the Glomerulus
PCT reabsorbs 80%
TALH reabsorbs 15%
CCD absorbs 5%
Normally 0% is released into the urine
How much bicarb is normally reabsorbed?
100%
Which portion of the CD is regulatable?
The collecting duct is regulatable
Describe the channels that mediate HCO3 reabsorption in the PCT?
Apical Membrane: Na/H Antiporter, H ATPase, Aquaporins
Basolateral Membrane: Na/K ATPase, Na/3HCO3 symporter
H+ is pumped into the lumen and reacts with HCO3 to form H2CO3, which is acted upon by CA to form H2O and CO2
CO2 diffuses into the cell and is acted upon by CA to form H2CO3, which breaks apart into H+ and HCO3
H+ is secreted into the lumen while HCO3 is reabsorbed into the blood with the Na/3HCO3 channel
What is NHE3?
NHE3 is an Na/H antiporter that release H+ into the lumen
What is NBCe1A?
NBCe1A releases HCO3 into the bloodstream in the PCT
How are H+ secretion and HCO3 reabsorption in the PCT related?
For every 1 H+ secreted into the lumen at the PCT, 1 HCO3 is reabsorbed into the blood
How is HCO3 reabsorption different in the TALH, in comparison to the PCT?
HCO3 secretion into the blood uses a HCO3/Cl transporter on the basolateral membrane instead of the Na/3HCO3 channel
Is HCO3 reabsorption in the DCT mediated by an Na/H exchanger?
No, an H ATPase is more important here
What is the function of Principal Cells in the collecting tubule?
Retain Na and secrete K
What is the function of alpha intercalated cells?
Secrete H+ and reabsorb HCO3
What is the function of beta intercalated cells?
Secrete HCO3 and reabsorb H+
Which proton pump is more important in alpha intercalated cells, H/K antiporters or H+ ATPase?
H+ ATPase is more important for secreting H+ in alpha intercalated cells
What does AE1 mediate?
AE1 is an HCO3/Cl exchanger in alpha intercalated cells that facilitates HCO3 reabsorption
What does Pendrin mediate?
Pendrin is an HCO3/Cl exchanger in beta intercalated cells that facilitates HCO3 secretion
How do alpha and beta intercalated cells interrelate?
Alpha and Beta cells exert opposite effects, and are activated/deactivated by dietary intake of H+/HCO3
What buffer is most prevalent in the nephron?
Bicarb acts as the main buffer until the collecting tubule, where phosphate and ammonia are the major urine buffers
What is meant by de novo bicarbonate formation in the CD?
Since there is little bicarbonate that reaches the CD, Bicarbonate is formed by:
Absorbing CO2 from the apical side
CO2 + H2O = HCO3 and H+ via CA
H+ is excreted into urine via H/K ATPase and H+ ATPase
HCO3 is reabsorbed into the bloodstream via AE1, a HCO3/Cl antiporter, and is “de novo” because the HCO3 formed is not reabsorbed from the lumen