Unit 2, L20 Acid Base 2 Flashcards
Define NEAP
Net Endogenous Acid Production, and it is an equivalent loss of HCO3 from the body that must be replaced
For acid base balance to be maintained
Acid must be excreted from the body at a rate equivalent to its addition
What is the amount of nonvolatile acids that is added to the body each day for a meat-containing diet, normal metabolism, and fecal HCO3 loss?
50-100 mEq/day for most adults
How are nonvolatile acids neutralized by bicarb?
Nonvolatile acids are immediately neutralized by bicarb in the ECF
To maintain acid-base balance, the kidneys must do what?
The kidneys must replenish the bicarb lost by neutralization of nonvolatile acids, a process called Renal Net Acid Excretion (RNAE)
Which is regulated, NEAP or RNAE?
RNAE, NEAP is not regulated
What will happen when the kidneys regulate RNAE
1) Replenish the HCO3 (new HCO3) lost by neutralization of nonvolatile acid
2) Kidneys must prevent loss of HCO3 in urine
How much does the PT reabsorb of bicarb
80%
How much does the TAL reabsorb for bicarb
10%
What is the excretion of bicarb?
0%
How much bicarb do we need each day?
50-100 mEq
How much H is secreted and what happens to it?
Nephrons secrete out about 4400 mEq and most of it will reabsorb the filtered load of bicarb
What is the predominant pathway for H secretion in the PT
NHE3 transporter, it is an Na/H exhanger, sends Na in and H out on the apical membrane q
What are the two different isoforms of CA and how do they function
1) CA-IV is present on the brush boarder, so the CO2 and H2O formed readily cross the luminal membrane and enter the cell
2) Ca-II is inside the cell, and this is where H and bicarb are produced
HCO3 is reabsorbed by two mechanisms in the PT, what are they
1) Na-HCO3 cotransporter, also called NBC1
2) Cl-HCO3 exchanger
In the PT, is there increased, decreased, or net reabsorption of Na and HCO3?
Net reabsorption
In the DT, bicarb is being reabsorbed by what transporter
AE1, moves bicarb out towards the blood and Cl into the cell
In the PT, is there H secretion?
No
In the DT, is there H secretion?
Yes, we have secretion from the alpha intercalated cells
In the distal tubule, for each H that is being secreted, what is happening with bicarb
For each H that is being excreted as titratable acid, one new HCO3- is being synthesized and reabsorbed
PT vs DT in terms of H secretion and bicarb
PT: No H acid secretion, and reabsorption of bicarb
DT: H excreted, bicarb synthesis, and reabsorption of bicarb
Beta intercalated cells will secrete what
Bicarb, not H
In the DT, bicarb is secreted through what transporter
Pendrin, it sends bicarb out and Cl into the cell
How is H reabsorbed in DT
V-ATPase will reabsorb H
Under meat-containing diets, what will dominate, H secretion or bicarb secretion?
H secretion will dominate
How much acid is normally excreted in urine?
50-100 mEq of acid, so urine is normally acidic
H can be removed in what two main forms
1) Titratable acids in the urine
2) NH4
What is the most important titratable buffer and why?
Phosphate, because of its relatively high concentration in urine and its ideal pKa
What is the percentage of Pi that is reabsorbed and excreted?
85% reabsorbed, 15% excreted
What is a titratable acid
Since urinary pH is bounded over the range of 7.4 to 4.4, only those weak acids with pKas within this range are titrable acids
What is ammonium and why is it in our urine?
Hydrogen ions that are not associated with Pi or other filtered bases are excreted as ammonium, and more H ions are excreted with ammonium than with filtered bases like Pi
NH4 production and its relationship with bicarb
NH4 is produced by the kidneys and its synthesis and subsequent excretion adds HCO3 to the ECF, and this is regulated in response to the acid-base requirements of the body
At pH 7.3, what form is ammonia in and because of this, what is the consequence for H
NH4 form, so ammonium, and H can be excreted
What is ammoniagenesis
Production of NH4 from glutamine in the PT
New bicarb is produced how
During the metabolism of glutamine by cells of the PT
What is critical for the excretion of NH4?
H secretion by the CD is critical for the excretion of NH4
If there is no H secretion, what happens to NH4
NH4 will be returned to the systemic circulation, converted to urea in the liver, and consume bicarb
What is the overall net result with bicarb and ammonium
1 new bicarb is returned to the systemic circulation for each proton excreted in the form of NH4 in the urine
What are the three quantities to consider when examining the net excretion of acid?
The amount of titratable acidity
The amount of ammonium
The amount of bicarbonate or free protons, if any
The steps to excrete a base
1) Freely filter bicarb
2) Reabsorb the majority of the filtered bicarb
3) Reabsorb some additional bicarb
4) Secrete some bicarb
5) Excrete alkaline urine containing bicarb
The steps to excrete an acid
1) Freely filter bicarb
2) Reabsorb the majority of the filtered bicarb
3) Reabsorb some additional bicarb
4) Secrete H and secrete NH4
5) Excrete acidic urine containing NH4
What is the equation for quantifying RNAE
RNAE = titratable acid excreted + NH4 excreted - HCO3 excreted
What will increase H secretion
Cellular acidosis
Endothelin
Cortisol
Ang II
What will increase ammoniagenesis
Cellular acidosis
Cortisol
Ang II
What will decrease Pi reabsorption
PTH
What will increase new bicarb synthesis
Titratable acid (Pi)
NH4 excretion
Rhbg and Rhcg
ECF volume expansion will do what for regulation of bicarb
ECF volume expansion will inhibit isosmotic reabsorption in the PT, which will inhibit bicarb reabsorption
ECF volume contraction will do what for regulation of HCO3
WIll stimulate bicarb reabsorption
Ang II will do what for regulation of bicarb
Stimulates Na-H exchange in the PT, which will stimulate bicarb reabsorption and increase blood bicarb concentration. This can cause contraction alkalosis, which can also be caused by loop diuretics or thiazide diuretics
Effect of the lungs on bicarb
Chronic changes in PCO2 alters the reabsorption of filtered bicarb
Increases in PCO2 increases the reabsorption of bicarb and decreases the PCO2 will decrease the reabsorption of bicarb
ET-1 will do what for H transport in the PT
Stimulate the insertion of Na/H antiporter into the apical membrane, and insertion of Na/3HCO3 symporter into the basolateral membrane in PT
Cortisol will do what for cellular H transport in the PT
Increase the abundance of the Na/H antiporter and Na/3HCO3 symporter in the PT
Ang II will do that for cellular H transport in the PT
Bind to the ang I receptor, stimulate H secretion and bicarb reabsorption by the PT
