ABG & Acid/base Regulation Flashcards
Define partial pressure of oxygen
The volume of oxygen dissolved in the arterial blood
Define partial pressure of co2
The volume of co2 dissolved in the arterial blood
Define base excess
The concentration of bases compared to the expected concentration
What will happen to partial pressure of oxygen and co2 if there is inadequate gas exchange in the lungs?
po2 will fall
pco2 will rise
What are the 3 ways pH is important in relation to maintaining the 3D structure of proteins
Maintaining enzyme structure so the substrate can bind to it
Maintain the structure of receptors so proteins like hormones can bind to them
Maintaining the shape of membrane transporters to allow exchange of substances in and out of cells
What is the equation for formation of carbonic acid and its dissociation?
h2o + co2 reversibly bing to become h2co3 which reversibly dissociates to h+ and hco3-
What breathing pattern causes respiratory acidosis?
Suboptimal ventilation/hypoventilation
What are pH, pco2 and base excess like when there is an uncompensated respiratory acidosis?
pH= low pco2= high BE= normal
What are pH, pco2 and base excess like when there is a partially compensated respiratory acidosis?
pH= starts to rise but not normal pco2= high BE= starts to rise
What are pH, pco2 and base excess like when there is a fully compensated respiratory acidosis?
pH= normal pco2= high BE= high
How does the body fix an uncompensated respiratory acidosis?
Tries to reduce h+ excess by increasing h2co3- via 2 phases:
Acute phase= co2 moves into RBCs, combines with water, dissociates to form hco3- which moves out of RBCs via AE1 transporter
Chronic phase= reabsorption of bicarbonate in the kidney
How many phases are there in correcting uncompensated respiratory acidosis? What organs/ calls are involved in each?
2 (acute and chronic)
Acute: involves RBCs and their AE1 transporter
Chronic: involves kidneys
Explain why hypoventilation causes a respiratory acidosis
Less air reaches the alveoli in the lungs, this reduces o2 vol in the lungs and reduces the concentration gradient for co2 to diffuse out of the blood. The post arterial blood now has more co2 in it which combines with water to form carbonic acid, this dissociates to give h+ and makes the blood more acidic
What breathing pattern causes respiratory alkalosis?
Hyperventilation
Explain why hyperventilation causes a respiratory alkalosis
There is more fresh air and o2 vol in the alveoli which creates a higher conc gradient for co2 to diffuse out of the blood. More co2 diffuses out so hte carbonic acid curves shifts to the left to make up for this. This reduces the amount of free h+ in the blood and increases pH
What are pH, pco2 and base excess like when there is an uncompensated respiratory alkalosis?
pH= high pco2= low BE= normal
What are pH, pco2 and base excess like when there is a partially compensated respiratory alkalosis?
pH= starts to reduce but is not normal yet pco2= low BE= starts to fall
What are pH, pco2 and base excess like when there is a fully compensated respiratory alkalosis?
pH= normal pco2= low BE= low
How does the body fix an uncompensated respiratory alkalosis?
It tries to increase the vol of h+ in the blood, it does this via one chronic phase where there is reduced reabsorption of hco3- from the kidneys. This causes a shift of the carbonic acid equation to the right so there are more h+ produced and pH starts to fall
How many phases are there in correcting uncompensated respiratory alkalosis? What organs/ calls are involved in each?
One phase only, just the acute phase. The kidneys are involved
Describe methods by which a metabolic acidosis may arise
Any method where there is lots of loss of hco3- eg diarrhoea that is watery or metabolic conditions that cause hco3- loss or cause h+ production eg lactic acid production
How are pH imbalances that are caused by metabolism fixed?
By altering ventilation
How is metabolic acidosis resolved?
By lowering the h+ content in blood, this is done by increasing ventilation. It will cause co2 to diffuse out of the blood faster do the carbonic acid equation will shift to the left and h+ ions will bind with hco3- and their conc in the blood will be reduced
What are pH, pco2 and base excess like when there is an uncompensated metabolic acidosis?
pH= low pco2= normal BE= normal
What are pH, pco2 and base excess like when there is a partially compensated metabolic acidosis?
pH= starts to rise pco2= starts to fall BE= starts to fall
What are pH, pco2 and base excess like when there is a fully compensated metabolic acidosis?
pH= normal pco2= low BE= low
Describe methods by which a metabolic alkalosis may arise
Vomiting causes an excessive loss of Hcl
How is metabolic alkalosis resolved?
By increasing h+ conc in the blood. This is done by initiating hypoventilation. Less co2 moves out of the blood and so the carbonic acid equation shifts to the right, more carbonic acid is produced, it dissociates and h+ conc in the blood rises
What are pH, pco2 and base excess like when there is an uncompensated metabolic alkalosis?
pH= high pco2= normal BE= normal
What are pH, pco2 and base excess like when there is a partially compensated metabolic alkalosis?
pH= starts to fall but isn't normal yet pco2= starts to rise BE= starts to rise
What are pH, pco2 and base excess like when there is a fully compensated metabolic alkalosis?
pH= normal pco2= high BE= high
Why doesnt oxygen saturation go down much when comparing arterial blood to venous blood?
Due to the sigmoid shape of the oxygen dissociation curve
Define pulmonary transit time
How long the blood is close enough to the respiratory exchange surface to exchange gases
Out of carbon dioxide and oxygen which equilibrates faster?
Carbon dioxide
What is an adequate pulmonary transit time?
0.75 secs
How is hydrogen ion conc converted to pH?
-log base 10 [h+]
Define co2 flux
The amount of co2 being produced
What are the usual units of co2 flux?
mL/min
What is the buffering capacity of blood?
Very high
Referring to acids and alkalis what does the suffix ‘osis’ mean?
Circumstances that lead to the state
Referring to acids and alkalis what does the suffix ‘aemia’ mean?
The actual state
Can there be an acidosis while there is an alkaemia?
Yes, acidosis refers to the circumstances and alkaemia is the state that the acidosis is trying to correct
