Session 5 - Renal Control Of Plasma Potassium Flashcards
What is the normal range for plasma pH?
7.35 - 7.45
Which two organs are the major control centre for the Carbon Dioxide / Hydrogen Carbonate buffer system?
The lungs control the Carbon Dioxide concentration
The Kidneys control the Bicarbonate concentration
What is the normal ratio for Hydrogen Carbonate: Carbon Dioxide in plasma?
20:1
How is a Respiratory Alkalaemia caused?
Hyperventilation leads to Hypocapnia
This increases the ratio of HCO3-:CO2 to > 20:1
More protons are now buffered in the plasma
Hence pH rises
How can the kidneys compensate for Respiratory Acidaemia?
If pCo2 rises then pH will fall. The kidneys will compensate for this by reducing excretion of bicarbonate.
More hydrogen ions now buffered so pH rises to normal levels
How does persistent vomiting cause a metabolic alkalosis?
- Protons are vomited out in the stomach acid
- More hydrogen ions are now needed to be made
- Production of protons also means more HCO3- are made
- These are transported straight into the blood
- More Protons buffered in blood -> pH rises
How is a Metabolic Acidaemia compensated for?
- If HCO3- is low, then CO2 needs to be lowered proportionally
- This can be done by increased ventilation by the lungs
- More CO2 removed to pH rises
Why can a Metabolic Alkalosis not be fully compensated for by the lungs?
This would require ventilation to fall dramatically depending on the severity of the alkalosis. Ventilation needs to remain relatively high in order to prevent hypoxia
How is HCO3- absorbed in the PCT?
- Na/K ATPase sets up gradient for Na entry into cells
- Protons pumped out of cell in exchange for Na
- H+ + HCO3- -> H20 + CO2, CO2 then enters cells
- CO2 reacts with H20 to make HCO3-
- HCO3- then travels through basolateral membrane + into plasma
By what two substances are Hydrogen ions buffered in the urine?
Ammonia and Phosphate
How can persistent vomiting cause hypokalaemia?
- Incraesing conc of HCO3-
- Body stops actively secreting Protons
- As proton secretion has stopped in kidneys less potassium is absorbed
What are some of the side effects of hypokalaemia?
- Tetany
- Parasthesia
- CVS problems
How may a metabolic acidosis be caused?
- Excess metabolic acids produced
- Acids are ingested
- Loss of HCO3-
- Problem with renal excretion of acid
What is the Anion Gap?
The difference between the sum of the measured concentrations of Sodium + Potassium and the sum of measured concentrations of Chloride and Hydrogen Carbonate.
Anion Gap = (Na+ + K+) - (Cl- + HCO3-)
Describe some effects of Acidaemia?
- Decreased enzyme function
- Decreased cardiac + skeletal muscle contractility
- Decreased glycolysis rate
- Decreased hepatic function
- Increased potassium in plasma
How does aldosterone effect potassium secretion?
- It increases the transcription of the sodium/potassium ATPase
- also increases transcription of eNaC and K+ channels
- hence more aldosterone = More potassium secretion
What is the relationship between plasma pH and secretion of potassium?
Acidaemia = Less potassium in parietal cells = Less secretion
Alkalaemia = More potassium in parietal cells = More secretion
How does Insulin effect ICF levels of Potassium?
- Potassium in splanchic blood stimulates insulin release
- Increase amounts of NA/K ATPases
- hence potassium conc rises in ICF
How does cell lysis effect ICF levels of Potassium?
Potassium released from ICF -> ECF
How does Aldosterone effect ICF levels of Potassium?
- Increased transcription of Na/K ATPase
- also increases eNaC and Potassium channels in apical membrane
- This increases ICF potassium
How does exercise effect ICF levels of Potassium?
- Skeletal muscle contraction gives net release or potassium
- Increased potassium in plasma
- Less ICF potassium
How do Catecholamines effect ICF levels of Potassium?
- Beta 2 agonists stimulate Na/K ATPase
- Hence ICF potassium increases
How does Plasma Hyperosmolarity effect ICF levels of Potassium?
- Hyperosmolarity causes water to move into ECF
- Potassium follows down conc gradient
- Potassium ICF conc falls
Name some causes of Hypokalaemia
- Inadequate intake of potassium
- Excessive loss (GI or Renal)
- Alkalosis
Name some causes of Hyperkalaemia
- Inadequate renal excretion
- Kidney Injury
- Low Mineralocorticoid effect
- Acidaemia
- High cell lysis
What is th effect of hypokalaemia on the heart?
- Hyperpolarises the RMP
- More fast Na+ channels now in active form
- Heart is more excitable
