Session 5 Flashcards
Define Hypercapnia
An increase in pCO2
Define Hypocapnia
A decrease in pCO2
Below what value is classified as Hypoxia?
8kPa - as has to drop to about this before Hb saturation is severely effected
Define Hyperventilation
Breathing more than you need to
Define Hypoventilation
Breathing less than you need to
What happens to gas levels in Hyperventilation?
pCO2 falls
pO2 rises
What happens to has levels in Hypoventilation?
pCO2 rises
pO2 falls
Why can you not correct a fall in pO2 by breathing more if pCO2 is the same?
Because correcting the Hypoxia will cause Hypocapnia
How do pCO2 effect pH? (When HCO3- is constant)
If pCO2 rises, pH drops
If pCO2 drops, pH rises
What happens if plasma pH drops below 7?
K+ rises
Enzymes become denatured
What happens if plasma pH rises above 7.6?
The free Ca2+ concentration decreases as Ca2+ goes into bones. This causes Tetany
Why do you have respiratory acidosis?
Hypoventilation occurs leading to Hypercapnia which causes plasma pH to fall
Why do you have respiratory alkalosis?
Hyperventilation occurs leading to Hypocapnia which causes plasma pH to rise
What does plasma pH depend on?
The ratio of pCO2 to HCO3-. This means that changes in pCO2 can be compensated for by changes in HCO3-
What controls HCO3-?
The kidneys
What compensates for respiratory alkalosis/acidosis?
The kidneys, but it takes 2-3 days as it is made and excreted relatively slowly
What is Metabolic acidosis?
The tissues produce acid which reacts with HCO3-. This decrease in HCO3- leads to a fall in pH
How is Metabolic acidosis compensated for?
Changing ventilation - Increased ventilation means decreased pCO2 so the pH will be restored to normal
What is Metabolic alkalosis?
The plasma HCO3- rises (e.g. due to vomiting as H+ in stomach replaced and H+ production has by product of HCO3-) which causes plasma pH to rise.
How is Metabolic alkalosis compensated for?
Decreased ventilation
How are respiratory changes in pH compensated for?
By the kidney
How are metabolic changes in pH compensated for?
By breathing
What determines breathing?
pH (pCO2) then pO2 as O2 doesn’t need to be tightly controlled as long as it is above 8kPa
What monitors arterial pO2?
Chemoreceptors in the carotid bodies and aortic bodies (They do not work unless the pO2 is very low)
What does a large decrease in pO2 stimulate?
Increased breathing
Changes in heart rate
Blood diversion to the brain
What senses changes in pCO2?
Central chemoreceptors in the medulla of the brain
Peripheral chemoreceptors too, but these are insensitive
How do central chemoreceptors detect changes in pCO2?
They respond to changes in pH of the Cerebrospinal fluid
How do the central chemoreceptors respond if pCO2 is too high?
They increase ventilation
How do the central chemoreceptors respond if pCO2 is too low?
They decrease ventilation
What happens if there is a short term increase in pCO2?
There is an increase in pH of the Cerebrospinal fluid which causes an increase in breathing
What happens if there is a long term increase in pCO2?
The Choroid plexus alters HCO3- concentration. This takes a few hours
