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► Med - Year 1 > Acid-Base Balance > Flashcards

Acid-Base Balance Flashcards

1
Q

List the rough percentages of reabsorption of the filtered load of HC03 throughout the PT, TAL, DT/CD, and out of nephron. What is take away message?

A

PT-80%
TAL-15%
DT/CD- 5%
output: 0%

The kidney wants to maintain and preserve the filtered load of HCO3-!

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2
Q

What are the main three roles of the kidney in terms of acid-base balance?

A
  1. reabsorb filtered load of HCO3
  2. Excrete non-volatile acids
  3. regenerate/replenish HCO3 that’s been consumed
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3
Q

What is a volatile acid?

A

One that breaks down into CO2

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4
Q

How much nonvolatile acid is excreted / day?

A

~140 mEq / Kg body weight / day

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5
Q

Net Acid Excretion Rate (NAE) equation

A

(UNH4V) + (UTAV) - (UHCO3*V)

TA= titratable acid = nonvolatile acid

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6
Q

Carbonic anhydrase is found in two regions of the proximal tubule. What is its function in both?

A

Inside cell: H2O + CO2 –> HCO3 + H+
(HCO3 gets reabsorbed, H+ gets secreted via the Na/H+ antiporter)

On luminal membrane: H+ + HC03 –> H2O + CO2
(CO2 diffuses down gradient and goes through cell membrane)

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7
Q

What are two major things that impact HCO3 reabsorption?

A
  1. Na reabsorption: if Na reabsorption increases, HCO3 reabsoprtion increases (due to Na/H antiporter, H gets secreted more, binds with HCO3, brings H2O and CO2 back into cell to make more HCO3 to get reabsorbed)
  2. CA inhibitors: blocks conversion of H2O + CO2 –> HCO3 + H+
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8
Q

Why do CA inhibitors make an effective diuretic?

A
  • Enzyme cant convert H2O + CO2 –> HCO3 + H+
  • less H+ gets secreted
  • less Na gets reabsorbed (antiporter)
  • diuretics block Na reabsorption
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9
Q

Outside of Acid/Base balance, what are 3 other regulators of HCO3 reabsorption?

A
  1. Filtered load of HCO3
  2. ECV (AII, SNS)
  3. K+ balance (if too much K+, gets put in cell, kicks out proton to maintain neutrality, intracellular pH increases)
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10
Q

What is the presence of CA in TAL, and how does it compare to in the PT?

A

CA is located only inside the cell, there is no CA in apical side. Reabsoprtion is thus limited since reaction doesn’t occur very quickly.

NB: H2O isn’t reabsorbed in the TAL!

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11
Q

Two main functions of Principal Cells in CD:

A
  1. reabsorb Na and H2O

2. secrete K+

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12
Q

Two types of intercalated cells in CD. Describe major differences/function

A
  1. alpha-IC - secrete acid via proton ATPase, H/K ATPase (both on apical side), and antiporter HCO3/Cl (on basal side, HCO3 getting reabsorbed)
  2. beta-IC - secrete base via antiporter HCO3/Cl (on apical side), and proton ATPase (on basal side, H+ getting reabsorbed).
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13
Q

Meat lovers make use of which intercalated cell the most?

A

Alpha-IC, since it secretes acid and there is a shit ton of acid in protein!

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14
Q

In addition to acid/base balance, what is another regulator of acid secretion?

A

For whatever reason, aldosterone stimulates alpha cells to secrete acid.

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15
Q

Titratable acids need to be excreted with associated proteins. Where does this buffering occurs in the nephron?

A

Collecting Duct

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16
Q

Which process is the most important aspect for acid base regulation?

A

Ammoniagenesis

17
Q

Via what process is consumed HCO3 regenerated/replenished?

A

Ammoniagenesis

18
Q

Breakdown of ____ turns into 2NH4 + 2HCO3. Where does this occur in the kidney?

A

glutamine, proximal tubule

19
Q

If the kidneys done excrete NH4, what happens to it?

A

Gets picked up by liver, converted to urea + 2H+

20
Q

NH4 is easily converted to NH3 + H+. Which form has a tough time crossing the membrane?

A

NH4+. Ammonia (NH3) is like COD, it can easily diffuse down its gradient

21
Q

Trace the major steps of ammonium (NH4) through the nephron

A
  • In the PT: H+ gets secreted (via Na/H antiporter) to join with NH3 in the lumen of the nephron
  • gets kicked out of lumen in the TAL due to lumen’s (+) charge due to small K conductance in apical membrane
  • NH4 –> NH3 + H+ in interstitial space
  • NH3 gets reabsorbed in CD, and thus even greater driving force to convert NH4–>NH3 in interstitial space
  • lots of H secretion of H+ in IC cells in CD (pH~4), traps ammonium
  • NH4 excreted
22
Q

Henderson–Hasselbalch equation

A

pH = 6.1 + log [HCO3]/ alpha*PCO2

where alpha = 0.03 (conversion factor mmHg–>mEq)

23
Q

cut off pH for acidosis and alkalosis

A

acidosis

24
Q

3 lines of defense (and time scale) to keep changes in pH at a minimum:

A
  1. ECF/ICF buffer–quick, seconds
  2. Respiratory compensation –> change in PCO2 –> change in pH – minutes to hours
  3. Renal Compensation/correction –> ammoniogenesis –hours to days
25
Q

ECF/ICF buffers as a line of defense (3)

A
  1. Phosphates (everywhere)
  2. proteins (plasma, albumin)
  3. CO2/HCo3 (everywhere)
26
Q

As ECF/ICF buffers, CO2/HCO3 is considered an “open” system while the other two are “closed.” What does this mean?

A 
Open = can change [ ], vary equilibrium
Closed = can't change concentrations, when there's an abnormality
27
Q

metabolic acidosis and compensation

A
  • due to decrease [HCO3]
  • compensation = decrease PCO2
  • increases net acid excretion
28
Q

metabolic alkalosis and compensation

A
  • due to increase [HCO3]
  • compensation = increase PCO2 (increase pCO2 –> decrease pH –> more acidic)
  • decrease net acid excretion
29
Q

respiratory acidosis and compensation

A
  • due increased PCO2 (which decreases pH= acidic)
  • compensation = buffers
  • increase net acid excretion
30
Q

respiratory alkalosis and compensation

A
  • due to decreased PCO2
  • compensation = buffers
  • decrease NAE
31
Q

What are the two forms of metabolic acidosis?

A
  1. Anion gap type

2. Non Anion gap

32
Q

What are causes of non-anion gap metabolic acidosis? (3)

A

GI losses (diarrhea), addition of mineral acid equivalents (HCl), renal tubular acidosis

33
Q

anion gap “equation”

A

[Na+] - [Cl-] - [HCO3-]

34
Q

What does a non-anion gap mean?

A

If add some acid H+A- to the system, the anion A- is used to measure the amount. If the anion of the acid is Cl-, then the decrease in HCO3 (to buffer the acid) will be matched by an increase in Cl, and the anion gap will be normal. However, if the anion of a nonvolatile acid is not Cl, then the anion gap will increase

35
Q

normal level for anion gap

A

8-16 mEQ/L

36
Q

Treat these 8 causes of acidosis differently than non-anion gap

A 
Methanol
Uremia (kidney failure)
Ketoacids (diabetic-DKA, alcoholic, starvation)
Paraldehyde
INH toxicity
Lactate
Ethanol/ehylene glycol
Salicyclate (from aspirin)

► Med - Year 1 (48 decks)

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