Acid-Base Buffering

Question 0

Henderson-Hasselbach solved for pH?

Answer 0

pH = pKa + log ( [buffer-] / [buffer-H] )

Question 1

Review: Normal plasma pH?

Normal intracellular pH?

Answer 1

Normal plasma pH: 7.4

Normal intracellular pH: 7.1

Question 2

Nit-picking difference between “acidemia” and “acidosis”?

Answer 2

Acidemia = low pH.
Acidosis = pathophysiological process that leads to low pH.

Question 3

3 ECF buffers?

Answer 3

Bicarb
Proteins
Inorganic phosphate

Question 4

3 ICF buffers?

Answer 4

Hemoglobin (in RBCs, obviously)
Proteins
Inorganic phosphate

Question 5

What organ has a reservoir of buffers that can be released?

Answer 5

Bone - lots of phosphate can be released in response to acid load.

Question 6

What is the Henderson-Hasselbach equation applied to bicarb/carbonic acid system?

Answer 6

pH = pKa + log ( [HCO3-] / (s * PCO2) )

Where pKa = 6.1, s = solubility coefficient = 0.03, and PCO2 is partial-pressure of CO2.

Question 7

Which organs regulate the 2 parts of the bicarb buffer system?

Answer 7

Lungs: regulate CO2.
Kidneys: regulate HCO3-

Question 8

Is having lungs good for acid-base balance?

Answer 8

Yep… PCO2 can be lowered even below that of environment’s.

Question 9

4 responses to increased H+ load?

Answer 9

Suppressed rate of endogenous acid production.
Buffering.
Compensatory hyperventilation.
Increased renal H+ excretion.

Question 10

Is extracellular or intracellular buffering quicker?

Answer 10

Extracellular buffering is quicker.

Question 11

4 jobs of the kidney in acid/base balance?

Answer 11

H+ excretion.
Inorganic acid anion excretion.
Reabsorb HCO3-.
Create new HCO3-.

Question 12

Where in the kidney does most bicarb synthesis happen?

Answer 12

In the DCT (but some happens in the proximal tubule).

Question 13

What’s the formula for urinary net acid excretion? (there are 4 components)

Answer 13

NAE = H+ + Titratable Acid + NH4+ - HCO3-.

but it’s mostly titratable acid - phosphate - and ammonium salts

Question 14

Review: Is bicarb reabsorbed as bicarb?

Answer 14

Nope. It’s converted to CO2 + H2O by carbonic anhydrase at the cell surface, then back to bicarb within the cell.

Question 15

8 factors affecting HCO3- reabsorption?

Answer 15

Delivery of HCO3- (GFR, tubular flow rate).
Blood pH and HCO3-.
Blood pCO2.
Carbonic anhydrase activity.
ECF volume status.
Endothelin, catecholamines.
Parathyroid hormone.
Serum K+.

Question 16

How does ECF volume affect HCO3- reabsorption?

Answer 16

Increases bicarb resorption via increased Na+/H+ exchange.

via A-II and catecholamines

Question 17

How do endothelins and catecholamines affect HCO3- reabsorption?

Answer 17

Increase HCO3- reabsorption via increased Na+/H+ exchange.

Question 18

How does parathyroid hormone affect HCO3- reabsorption?

Answer 18

Decreases HCO3- reabsorption by inhibiting Na+/H+ exchange.

Question 19

How does hyperkalemia affect intracellular pH?

What’s the most important result of this?

Answer 19

Extra K+ moves into cells, driving H+ to move out.
ICF pH is increased.
The important result is decreased intracellular ammoniagenesis… in renal tubules.

Question 20

How does hypokalemia affect intracellular pH?

Important result of this?

Answer 20

Hypokalemia -> decreased intracellular pH (H+ moves into cells).
This stimulates increased renal ammoniagenesis.

Question 21

When bicarb is synthesized in the proximal tubule?

Answer 21

CO2 + OH- -> HCO3-

the OH-‘s proton has been buffered by something else

Question 22

H+ secretion in the PCT is done via Na+/H+ exchangers.
How is H+ secretion done in the collecting tubules?
What cells does this happen in?

Answer 22

H+/K+ exchanger.
H+ ATPase.
(this results in bicarb reabsorption)
This happens in alpha-intercalated cells.

Question 23

4 factors affecting distal H+ secretion?

Answer 23

Aldosterone.
Transepithelial voltage.
Buffer availability (Pi, NH3).
Endothelin.

Question 24

How does aldosterone increase H+ secretion?

Answer 24

Increased ENaC activity -> more Na+ reabsorption.

This creates an EC gradient that drives increased H+ and Na+ excretion.

Question 25

Biochemical pathway of ammonia generation?

Where, intracellularly, does this happen?

Answer 25

Glutamine -> glutamate -> alpha-ketoglutarate.
Each step produces NH3.
This happens in the mitochondria (mostly in the proximal tubule).

Question 26

What happens to NH4+ if it’s reabsorbed?

Answer 26

It’s made into urea in the liver, consuming bicarb.

Question 27

Through what channels does NH3/NH4+ move from blood to lumen in the collecting duct?

Answer 27

Rhbg and Rhcg

Question 28

Lower urinary pH corresponds with increased NH4+ / NH3 excretion.

Answer 28

That makes sense..