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Flashcards in Acid-Base Buffering Deck (29):
0

Review: Normal plasma pH?
Normal intracellular pH?

Normal plasma pH: 7.4
Normal intracellular pH: 7.1

1

Henderson-Hasselbach solved for pH?

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

2

Nit-picking difference between "acidemia" and "acidosis"?

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

3

3 ECF buffers?

Bicarb
Proteins
Inorganic phosphate

4

3 ICF buffers?

Hemoglobin (in RBCs, obviously)
Proteins
Inorganic phosphate

5

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

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

6

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

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

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

7

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

Lungs: regulate CO2.
Kidneys: regulate HCO3-

8

Is having lungs good for acid-base balance?

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

9

4 responses to increased H+ load?

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

10

Is extracellular or intracellular buffering quicker?

Extracellular buffering is quicker.

11

4 jobs of the kidney in acid/base balance?

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

12

Where in the kidney does most bicarb synthesis happen?

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

13

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

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

(but it's mostly titratable acid - phosphate - and ammonium salts)

14

Review: Is bicarb reabsorbed as bicarb?

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

15

8 factors affecting HCO3- reabsorption?

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+.

16

How does ECF volume affect HCO3- reabsorption?

Increases bicarb resorption via increased Na+/H+ exchange.
(via A-II and catecholamines)

17

How do endothelins and catecholamines affect HCO3- reabsorption?

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

18

How does parathyroid hormone affect HCO3- reabsorption?

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

19

How does hyperkalemia affect intracellular pH?
What's the most important result of this?

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

20

How does hypokalemia affect intracellular pH?
Important result of this?

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

21

When bicarb is synthesized in the proximal tubule?

CO2 + OH- -> HCO3-
(the OH-'s proton has been buffered by something else)

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?

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

23

4 factors affecting distal H+ secretion?

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

24

How does aldosterone increase H+ secretion?

Increased ENaC activity -> more Na+ reabsorption.
This creates an EC gradient that drives increased H+ and Na+ excretion.

25

Biochemical pathway of ammonia generation?
Where, intracellularly, does this happen?

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

26

What happens to NH4+ if it's reabsorbed?

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

27

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

Rhbg and Rhcg

28

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

That makes sense..