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Renal Physiology > Acid-Base Balance > Flashcards

Acid-Base Balance Flashcards

1
Q

What is the definition of a body fluid buffer?

A

Molecule that helps to maintain pH within a normal range

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2
Q

What are the Buffers in our bodies?

A
  1. HCO3- (ECF)
  2. Phosphate and Proteins (ICF)
    - main place for buffering in the body
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3
Q

How are acids and bases moved between ECF and ICF?

A

K+/H+ Exchanger which can go IN BOTH DIRECTIONS depending on needs of the body

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4
Q

In the case of Acidosis, what action would the K+/H+ Exchanger take?

A
  1. H+ is moved into the cell

2. K+ is moved into the ECF

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5
Q

In the case of Alkalosis, what action would the K+/H+ Exchanger take?

A
  1. H+ is moved into the ECF

2. K+ is moved into the cell

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6
Q

What effect does Hypoventilation have on the body’s acidity?

A

Hypoventilation=Acidosis

  1. Increase in CO2
  2. Decreases pH
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7
Q

What effect does Hyperventilation have on the body’s acidity?

A

Hyperventilation=Alkalosis

  1. Decreases in CO2
  2. Increases pH
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8
Q

Bicarbonate:

A
  1. Freely Filtered
  2. 24 mmol/L
  3. Filtered Load= 4320 mmol/day
  4. Virtually entirely REABSORBED
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9
Q

Simplified Overview of Renal Acid-Base Handling:

A
  1. Proximal Tubule: Kidneys reabsorb Bicarbonate and secrete NH4+
  2. Ascending Limb and Distal Tubule: Kidneys secrete either H+ or HCO3- to balance NET Input
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10
Q

What is the Proximal Tubule Mechanism for Bicarbonate Reabsorption?

A
  1. Inside of Proximal Tubule cells, H2O and CO2 come together to form H2CO3 (Carbonic Acid)
  2. Carbonic Anhydrase breaks down H2CO3 into H+ and HCO3-
  3. Na+/H+ Exchanger on Apical Membrane pumps H+ into the lumen and Na into the cell (NOTE: Angiotensin II can increase this exchange)
  4. H+ ion in the lumen combines with a filtered HCO3 to produce H2O and CO2 (Lose 1 filtered HCO3)
    5A. Na/HCO3 Symporter on the Basolateral Membrane pumps Na and HCO3 out of the cell and into the Blood (Gain 1 blood HCO3)
    OR
    5B. Cl/HCO3 Antiporter on Basolateral Membrane pumps one HCO3 into the blood and Cl into the cell

IMPORTANT: This is the “effective” Reabsorption of an HCO3- molecule without moving it across the membranes

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11
Q

What are the Net results of Proximal Tubule Bicarbonate Reabsorption?

A

NO NET CHANGE IN PLASMA BICARBONATE

  1. Filtered Bicarbonate disappears (H2O and CO2)
  2. Bicarbonate produced inside cell enters blood
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12
Q

Does Bicarbonate reabsorption make Urine more acidic?

A

NO, the H+ ion that is secreted into the urine combines with HCO3 to produce CO2 AND H2O

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13
Q

What is the Distal Tubule Mechanism for Bicarbonate Reabsorption in ALPHA Intercalated Cells?

A

HCO3 REABSORPTION

  1. Inside of Distal Tubule cells, H2O and CO2 come together to form H2CO3 (Carbonic Acid)
  2. Carbonic Anhydrase breaks down H2CO3 into H+ and HCO3-
    ENERGY IS REQUIRED TO PUMP H+ INTO THE URINE:
    3A. Proton Pump on the Apical Membrane utilizes ATP to put H+ into Urine using Primary Active Transport
    OR
    3B. H+/K+ ATPase on the Apical Membrane pumps a H+ out into the Urine and a K+ into the cell
  3. H+ pumped out of the cell combines with a Filtered HCO3 in the Urine to form H2O and CO2
  4. Cl/HCO3 Antiporter on Basolateral Membrane pumps one HCO3 into the blood and Cl into the cell
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14
Q

What is the Distal Tubule Mechanism for Bicarbonate Reabsorption in BETA Intercalated Cells?

A

HCO3 SECRETION

  1. Inside of Distal Tubule cells, H2O and CO2 come together to form H2CO3 (Carbonic Acid)
  2. Carbonic Anhydrase breaks down H2CO3 into H+ and HCO3-
    ENERGY IS REQUIRED TO PUMP H+ INTO THE BLOOD:
    3A. Proton Pump on the Basolateral Membrane utilizes ATP to put H+ into Blood (Primary Active Transport)
    OR
    3B. H+/K+ ATPase on the Basolateral Membrane pumps a H+ out into the Blood and a K+ into the cell
  3. H+ pumped out of the cell and into the blood increasing pH
  4. Cl/HCO3 Antiporter on Apical Membrane secretes one HCO3 into the urine and takes a Cl into the cell
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15
Q

In the Distal Tubule, when would the BETA Intercalated Cells be ACTIVE while the ALPHA Intercalated Cells are INACTIVE?

A

During Alkalosis

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16
Q

What happens in a Base load situation?

A

You are loaded with base, so Bicarbonate excretion happens

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17
Q

What happens in an Acid load situation? Simplified

A
  1. The Acid load reduces the amount of Bicarb in the blood
  2. Kidney needs to replace lost Bicarb by generating NEW Bicarb
  3. H+ ions are secreted via NH4+ and Titratable Acids
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18
Q

Can a H+ ion be free flowing in the urine?

A

NO

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19
Q

What is the purpose of Titratable Acids and what is their mechanism?

A

Purpose: Excrete excess H+ and increase HCO3- concentration in the blood

  1. Inside of Distal Tubule cells, H2O and CO2 come together to form H2CO3 (Carbonic Acid)
  2. Carbonic Anhydrase breaks down H2CO3 into H+ and HCO3-
    ENERGY IS REQUIRED TO PUMP H+ INTO THE URINE:
    3A. Proton Pump on the Apical Membrane utilizes ATP to put H+ into Urine using Primary Active Transport
    OR
    3B. H+/K+ ATPase on the Apical Membrane pumps a H+ out into the Urine and a K+ into the cell
  3. H+ pumped out of the cell combines with a Filtered HPO4 creating H2PO4
  4. H2PO4 Titratable Acid is excreted in the urine lowering blood H+ levels
  5. Cl/HCO3 Antiporter on Basolateral Membrane pumps NEW HCO3 into the blood and Cl into the cell

NET GAIN of 1 HCO3 in blood

20
Q

Every Titratable Acid found in the Urine corresponds to…

A

Every Titratable Acid found in the Urine coincides to 1 NEW HCO3 put into the blood

21
Q

What happens when the fixed amount of Titratable Acids in the body are all utilized?

A

By creating Ammonium

22
Q

From what part of the Nephron are Titratable Acids secreted?

A

“TAD T”

Distal Tubule

23
Q

From what part of the Nephron is Ammonium secreted?

A

“APT”

Proximal Tubule

24
Q

What Amino Acid is the basis for creating Ammonium and where is it made?

A
  1. Glutamine

2. Made in the Liver by catabolism of proteins

25
Q

What are the products of the metabolism of Glutamine? Where does this take place?

A
  1. Glutamine is taken up by Proximal Tubule cells

2. Produces 1 Bicarb (reabsorbed into blood) and NH4+ (secreted into the Lumen)

26
Q

Is there a limit to Acid load reduction via NH4+ secretion?

A

NO, NH4+ secretion is unlimited but there is a delay due to the enzymes necessary to convert

27
Q

What Acid/Base processes are carried out in each part of the Nephron?

A
  1. Proximal Tubule:
    A. Reabsorbs HCO3
    B. Produces NH4+ (if too much Acid)
  2. Ascending Limb:
    A. Reabsorbs HCO3
  3. Distal Tubule and Collecting Duct:
    A. Reabsorbs HCO3
    B. Secretes HCO3
    C. Secretes Titratable Acids
28
Q

What are the three ways that one can alter Acid/Base Levels?

A
  1. HCO3 Excretion in the Urine
  2. Titratable Acid Secretion and the formation of NEW HCO3
  3. Glutamine Metabolism resulting in NEW HCO3 and excreted NH4+
29
Q

What is the formula for Net Acid Excretion (NAE)?

A

NAE= (TA +NH4) - HCO3

  • all figures measured from urine
  • normally HCO3 is 0 unless Alkalosis
30
Q

In a situation where a person ingests excess acid, what is likely to happen to their Net Acid Excretion (NAE)?

A
  1. Urine Titratable Acid will increase but will plateau
  2. NH4+ concentration in the urine will increase dramatically
  3. NAE will increase dramatically (it is the sum of TA and NH4 in the urine)
31
Q

Does NH4+ affect Urine pH levels?

A

Yes, it lowers Urine pH levels making it more acidic

32
Q

Does the presence of Titratable Acids affect Urine pH levels?

A

No, Titratable Acids are neutral molecules

33
Q

In a situation where a person ingests excess base, what is likely to happen to their Net Acid Excretion (NAE)?

A
  1. HCO3 will be secreted into the urine for excretion via BETA Intercalated Cells located in the Distal Tubule
  2. Some NH4+ may still be secreted due to a delay
  3. NAE will be NEGATIVE
34
Q

A decrease in pCO2 would result in?

A

Alkalosis

35
Q

A decrease in HCO3 would result in?

A

Acidosis

36
Q

A decrease in pCO2 would result in?

A

Acidosis

37
Q

A decrease in HCO3 would result in?

A

Alkalosis

38
Q

What are the two causes of Acidosis?

A
  1. Acid Gain

2. Base (HCO3-) Loss

39
Q

What are some reasons for Acid Gain?

A
  1. Decreased Respiration as in Emphysema, Chronic Bronchitis
  2. Renal Failure
  3. Keto Acids (Diabetes)
40
Q

What are some reasons for Base Loss?

A

Diarrhea

41
Q

How can you differentiate Acidosis due to Acid gain or Base loss?

A

ANION GAP
-AG=Na-(Cl+HCO3)

  1. Normal Range (8-12) indicates Base Loss
  2. Increased Anion Gap indicates Acid gain
42
Q

Why does the Anion Gap stay within normal range if Acidosis is caused by a Base Loss?

A

When HCO3- is lost, it is replaced by Cl-

43
Q

Why does the Anion Gap increase if Acidosis is caused by Acid Gain?

A

Acids are an Anion and will increase the Anion Gap

44
Q

What are the two causes of Alkalosis?

A
  1. Fixed Acid Loss

2. Base (HCO3-) Gain

45
Q

What are some reasons for Fixed Acid Loss?

A
  1. Hyperventilation (loss of CO2)

2. Vomiting (loss of stomach acid)

46
Q

What are some reasons for Base Gain?

A
  1. Bicarb Overdose (hard)

2. Chronic Diuretic Usage

Renal Physiology (7 decks)

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