Session 6 Flashcards
What is the normal plasma pH range?
7.38 7.42
Define Alkalaemia
A change in pH of the plasma above 7.42.
What does Alkalaemia cause?
Decreased free calcium in the ECF
Increased excitability of nerves –> Paraesthesia & Tetany
Define Acidaemia
A change in pH of the plasma below 7.1
What does Acidaemia cause?
Effects enzymes –> Decreased cardiac and skeletal muscle contractility, decreased Glycolysis, decreased Hepatic function, Increased K+
What ratio does pH depend on?
HCO3- to CO2
What determines CO2?
Respiration. Controlled by chemoreceptors and disturbed by respiratory disease
What determines HCO3-?
Kidney control and disturbed by metabolic diseases
What does Hypoventilation cause?
Hypercapnia
This causes a decrease in plasma pH
Respiratory Acidosis
What does Hyperventilation cause?
Hypocapnia
This causes an increase in plasma pH
Respiratory Alkalosis
How are respiratory acidaemia/alkalaemia compensated?
The kidneys will increase HCO3- (For acidaemia) and decrease HCO3- (For alkalaemia)
Why does Metabolic acidosis occur?
The tissues release more H+ into the plasma. (pH decreases). HCO3- binds this and therefore becomes depleted.
How does the body compensate Metabolic acidosis?
Peripheral chemoreceptors increase ventilation
Why does Metabolic alkalosis occur?
Plasma HCO3- is increased (Can be from vomiting)
So pH rises
How does the body compensate Metabolic acidosis?
Can only partially compensate as the ventilation needs to be decreased, but still has to fulfill the O2 needs
How can the kidneys correct pH problems due to respiratory issues?
They can create more HCO3- or vary excretion of HCO3- (Can lose HCO3- easily, but if want to increase HCO3- need to make sure they reabsorb all and make more)
How is HCO3- made in the kidneys?
By the metabolic activity of the kidneys; it makes large quantities of CO2 which react with water to make HCO3- and H+ (excreted)
ALSO, make it from Amino acids, producing NH4- which is excreted
What buffers H+ in the urine?
Phosphate
What is the cellular response to acidosis?
Enhanced Na+/H+ exchange Full recovery of all HCO3- Enhanced ammonium production in PCT Enhanced activity of H+ ATPase in DCT Increased capacity to transport HCO3- from tubular cells to ECF
What can happen when HCO3- reacts with H+?
To maintain electroneutrality, HCO3- is replaced by another anion. This anion can vary depending on where the H+ is coming from eg lactic acid & lactate
Define Anion gap
Difference in the measured cations and measured anions in serum, plasma, or urine. Normally 10-15mmol/L
Why is the Anion gap useful?
It shows when HCO3- has been replaced with other anions therefore its decreased.
What happens to the anion gap when there is an issue within the body? (that is not the Kidneys)
It increases
What happens to the anion gap when there is an issue with the Kidneys?
It will be normal, but the blood will be acidic
How does renal correction for acidosis work?
A decrease in the intracellular tubular cell pH stimulates acid secretion and HCO3- recovery so there is an increased HCO3- conc.
How can you correct the pH after vomiting?
There is increased HCO3-, but the kidney can only excrete it if you correct the dehydration problem (as the kidney is trying to save solutes to keep water)
Why can you not give HCO3- infusions to people with high HCO3-?
Makes sense as HCO3- would be excreted, but the body is trying to keep other electrolytes and in the process would keep HCO3- as well. Therefore it would not work.
What is Hyperkalaemia associated with?
Metabolic acidosis
What is Hypokalaemia associated with?
Metabolic alkalosis
What does Hypokalaemia cause?
Intracellular pH of tubule cells acidic which favours H+ excretion and HCO3- recovery. Leading to metabolic alkalosis
What does Hyperkalaemia cause?
Intracellular pH to become alkaline which favours HCO3- excretion therefore get metabolic acidosis
Why is HCO3- not normally depleted?
The kidneys recover all HCO3-
The PCT makes HCO3- from amino acids, putting NH4- into urine
The DCT makes HCO3- and H+ from CO2. H+ is buffered in urine by phosphate and ammonia
