Control of Plasma pH Flashcards
State the normal plasma pH range
7.35-7.45
Compare Acidaemia and Acidosis
Is Acidaemia or Alkalaemia more dangerous?
Acidaemia is low blood pH due to acidosis
Alkalaemia is more dangerous
How does Alkalaemia affect Ca and nerves?
- Reduces solubility of Ca salts, so free Ca2+ leaves ECF and binds to bone and proteins-> Hypocalcaemia
- This makes nerves more excitable-> Parasthesia and Tetany (Uncontrolled muscle contractions)
What is the mortality rate if pH is above;
- 7.55
- 7.65
- pH>7.55 mortality: 45%
- pH>7.65 mortality: 80%
How does Acidaemia affect K+ movement?
When are effects of Acidaemia seen? When is it life threatening?
- Affects enzyme function, leading to K+ movement out of cells-> Hyperkalaemia
- Effects seen below pH 7.1
- Life threatening below pH 7.0
The ECF [H+] is very low so small amounts of acid would change pH dramatically. This is buffered by H+ binding to various sites
What is the most important ECF buffer for H+?
The CO2/ HCO3 system
Compare Respiratory Acidaemia and Alkalaemia
How are they compensated really?
- Acidaemia: Rises in pCO2
- Renal compensation: Increased HCO3
- Alkalmaemia: Falls in pCO2
- Renal compensation: Decreased HCO3
Compare Metabolic Acidosis and Alkalosis
How are they compensated by the respiratory system?
- Acidosis: Decreased HCO3
- Respiratory compensation: Reduced pCO2 (hyperventilation)
- Alkalosis: Increased HCO3
- Respiratory compensation: Increased pCO2 (hypoventilation)
Why is Respiratory compensation of metabolic alkalosis limited?
Hypoventialtion is limited as it can cause hypoxaemia
If acid is produced metabolically, recovery of l filtered HCO3 will be insufficient to restore plasma [HCO3].
How does the kidney compensate?
- Kidney makes HCO3 (normally only made in RBCs)
- The byproduct of this, H+, must be excreted into urine
- To prevent a damaging urinary acidity, the H+ must be buffered by other filtered substances or by buffers made in the kidney
How much HCO3 is reabsorbed in;
- PCT
- TAL
- DCT, via Intercalated cells
PCT: 80-90%
TAL: Up to 15%
DCT, Intercalated cells: Remaining
(Overall, 100% of HCO3 is reabsorbed)
Describe HCO3 reabsorption in CD Intercalated cells
- H-ATPase on AM pumps H+ out (Na gradient too low to use NHE)
- CO2 enters cell and reacts with water-> H2CO3 which dissociates into H+ and HCO3-
- New HCO3- ions enter blood via HCO3-Cl Antiport on BM
Compare H+ buffering systems in PCT and DCT
PCT;
- NH3 from Glutamine diffuses into lumen and combines with H+-> NH4+
DCT;
- H+ pumped out via H-ATPase into lumen and combines with Monobasic phosphate (HPO4 2-)-> H2PO4-
Describe how HCO3 is created in PCT (and also some in DCT)
- Glutamine broken down into NH4+ and Alpha-ketoglutarate
- NH4+ dissociates into NH3 and H+, NH3 diffuses into lumen and binds to H+ to reform NH4+ (in lumen)
- Alpha-ketoglutate breaks down into 2 HCO3 ions, which enter blood via Na-HCO3 symport on BM
How does ECF pH affect secretion of acid by kidney?
Why is this done?
Fall in pH-> Increased acid secretion into lumen
To prevent HCO3 depletion (Used to neutralise pH)
Why does acidosis cause Hyperkalaemia?
- More H+ enters cell from ECF, so more K+ enters ECF from cell
- Less K+ excreted in distal nephron
(In alkalosis, less K+ enters ECF and more is excreted)
Why does Hyperkalaemia cause acidosis?
- Tubular cells more alkaline, as H+ moves out of cells and K+ moves in
- To counter alkaline, HCO3 excreted in blood
What are 4 causes of metabolic acidosis
- Excess acid production metabolically (Lactic)
- Acid ingestion
- Impaired renal acc excretion
- HCO3 loss
If excess acid is produced metabolically, what replaces HCO3 in plasma?
The associated anion
This influences the anion gap
What is the Anion gap? (Normally 8-14mM)
How does anion gap change when HCO3 is replaced by an anion not included in the calculation group?
Difference between combined sum of [K] and [Na] and combined sum of [Cl] and [HCO3]
Anion gap increases when HCO3 replaced (Renal acidosis doesn’t change anion gap as Cl replaces HCO3)
What does the anion gap represent?
ECF level of unmeasured ions
How do we differentiate between ;
- Renal compensation of respiratory alkalosis
- Respiratory compensation of metabolic acidosis
Anion gap will be increased in metabolic acidosis
Explain the effect of Ethylene Glycol on the Anion Gap if ingested
What are the 2 substances this chemical is found in?
- Increases anion gap
- Due to acids produced by its metabolism
- Engine coolants
- Anti freeze
(Can be ingested as suicide attempt/ accident)
List 4 signs/ symptoms of Ethylene Glycol ingestion
CNS related;
- Slurred speech
- Confusion
- Stupor
- May be misdiagnosed with alcohol intoxication
