Lecture 17: Renal Control of Acid-Base Balance Flashcards
What metabolic acid sources are eliminated in a volatile way?
What does this mean?
Glucose and Fat
-can be converted into gaseous forms and be eliminated by lungs
What metabolic acid sources are eliminated in a fixed way?
What does this mean?
Glucose, Cysteine, and Phosphoprotein
-incomplete metabolism and eliminated via kidneys
What is a buffer solution?
Aqueous solution consisting of a mixture of:
- weak acid and its conjugate base
- weak base and its conjugate acid
What are some major buffer systems of the body?
1) Bicarbonate Buffer
2) Phosphate buffer
3) Protein buffer (e.g. hemoglobin and hisitidine )
How do plasma proteins and hemoglobin buffer hydrogen ions?
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
During acidemia, how does the ICF compensate for this?
Exchange potassium for increased levels of hydrogen in ECF
During alkalemia, how does the ICF compensate for this?
Donate hydrogen to ECF and allowing more potassium to enter cell
What is the Henderson-Hasselbalch equation for bicarbonate?
ph = 6.1 + log {[HCO3-] / [H2CO3-]}
ph = 6.1 + log {[HCO3-] / [0.03 x PCO2]}How does hyperventilation affect pH?
Increases pH
- Less carbon dioxide shifts balance toward left
- Less hydrogen available
How does hypoventilation affect pH?
Decreases pH
- More carbon dioxide shifts balance toward right
- More hydrogen available
How is bicarbonate reabsorbed in the proximal tubule?
1) Na+/HCO3- symporter
2) Cl-/HCO3- antiporter
What is the role of phosphate buffering of secreted hydrogen ions?
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
How can new bicarbonate be generated?
Glutamine breaks down into bicarbonate and ammonium
-bicarbonate is reabsorbed
What happens to the ammonium generated by glutamine?
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
Describe α-intercalated cells in collecting ducts.
Secretes hydrogen ions
Reabsorbs bicarbonate
Describe β-intercalated cells in collecting ducts.
Reabsorbs hydrogen ions
Secretes bicarbonate
How is net acid excretion calculated?
NAE= Flow Rate x {[NH4+] + [TA] - [Bicarbonate]}
What is the net acid excretion?
Net amount of acid excreted in the urine per unit time
-must equal nonvolatile acid production to maintain acid-base balance
What are titratable acids?
Salts of primary phosphate
- includes creatinine
- ⅓ of NAE
What is renal tubular acidosis?
Accumulation of acid in the body due to a failure of the kidneys to appropriately acidify the urine
Describe renal tubular acidosis type I.
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
Describe renal tubular acidosis type II.
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
Describe renal tubular acidosis type IV.
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
