Lecture 17: Renal Control of Acid-Base Balance

Question 1

What metabolic acid sources are eliminated in a volatile way?
What does this mean?

Answer 1

Glucose and Fat

-can be converted into gaseous forms and be eliminated by lungs

Question 2

What metabolic acid sources are eliminated in a fixed way?

What does this mean?

Answer 2

Glucose, Cysteine, and Phosphoprotein

-incomplete metabolism and eliminated via kidneys

Question 3

What is a buffer solution?

Answer 3

Aqueous solution consisting of a mixture of:

• weak acid and its conjugate base
• weak base and its conjugate acid

Question 4

What are some major buffer systems of the body?

Answer 4

1) Bicarbonate Buffer
2) Phosphate buffer
3) Protein buffer (e.g. hemoglobin and hisitidine )

Question 5

How do plasma proteins and hemoglobin buffer hydrogen ions?

Answer 5

Hemoglobin absorbs CO2 which dissociates into H+ and HCO3-
Option 1: HCO3- can exit RBC via HCO3-/Cl- exchanger
Option 2: Hemoglobin can bind with CO2 and leave via lungs

*Mixture of both will maintain blood pH at 7.4

Question 6

During acidemia, how does the ICF compensate for this?

Answer 6

Exchange potassium for increased levels of hydrogen in ECF

Question 7

During alkalemia, how does the ICF compensate for this?

Answer 7

Donate hydrogen to ECF and allowing more potassium to enter cell

Question 8

What is the Henderson-Hasselbalch equation for bicarbonate?

Answer 8

ph = 6.1 + log {[HCO3-] / [H2CO3-]}
ph = 6.1 + log {[HCO3-] / [0.03 x PCO2]}

Question 9

How does hyperventilation affect pH?

Answer 9

Increases pH

• Less carbon dioxide shifts balance toward left
• Less hydrogen available

Question 10

How does hypoventilation affect pH?

Answer 10

Decreases pH

• More carbon dioxide shifts balance toward right
• More hydrogen available

Question 11

How is bicarbonate reabsorbed in the proximal tubule?

Answer 11

1) Na+/HCO3- symporter

2) Cl-/HCO3- antiporter

Question 12

What is the role of phosphate buffering of secreted hydrogen ions?

Answer 12

1) HCO3- is reabsorbed
2) H+ is secreted into tubular lumen and binds with NaHPO4-
3) NaH2PO4 is excreted in urine

*Prevents hydrogen buildup and acidity

Question 13

How can new bicarbonate be generated?

Answer 13

Glutamine breaks down into bicarbonate and ammonium

-bicarbonate is reabsorbed

Question 14

What happens to the ammonium generated by glutamine?

Answer 14

Option 1: NH4+ –> NH3, which is secreted into tubular lumen
Option 2: NH4+ is directly secreted into tubular lumen in exchange for sodium entering cell
-replaces NK2C transporter

In the tubular lumen, NH3 can bind with hydrogen ions to become ammonium again and is excreted

Question 15

Describe α-intercalated cells in collecting ducts.

Answer 15

Secretes hydrogen ions

Reabsorbs bicarbonate

Question 16

Describe β-intercalated cells in collecting ducts.

Answer 16

Reabsorbs hydrogen ions

Secretes bicarbonate

Question 17

How is net acid excretion calculated?

Answer 17

NAE= Flow Rate x {[NH4+] + [TA] - [Bicarbonate]}

Question 18

What is the net acid excretion?

Answer 18

Net amount of acid excreted in the urine per unit time

-must equal nonvolatile acid production to maintain acid-base balance

Question 19

What are titratable acids?

Answer 19

Salts of primary phosphate

• includes creatinine
• ⅓ of NAE

Question 20

What is renal tubular acidosis?

Answer 20

Accumulation of acid in the body due to a failure of the kidneys to appropriately acidify the urine

Question 21

Describe renal tubular acidosis type I.

Answer 21

Build of hydrogen ions in α-intercalated cells, increasing hydrogen ions in blood as result (acidemia)

• H+ ATPase or H+/K+ ATPase channels on apical side might not be working
• Autoimmune disorder
• certain medication

Question 22

Describe renal tubular acidosis type II.

Answer 22

In PCT, bicarbonate is not properly reabsorbed so hydrogen in blood cannot bind with bicarbonate, resulting in acidemia

• bicarbonate instead is excreted via urine since its not properly absorbed by brush border cells
• Seen in Fanconi Syndrome

Question 23

Describe renal tubular acidosis type IV.

Answer 23

Low aldosterone or failure to respond to it

• high potassium levels inhibit ammonia production and hydrogen ions cannot bind with ammonia
• increases hydrogen levels in blood
• hyperkalemia present as well