Oxygen Transport & pH homeostasis Flashcards
What percentage of oxygen is physically dissolved in blood plasma?
~1.5%
Each polypeptide has a haem group capable of binding to oxygen, how many polypeptides make up a haemoglobin protein?
4
What is the most common type of haemoglobin found in an adult’s blood?
HbA (2 alpha and 2 beta chains)
What features would you see from PaO2 and SpO2 levels from someone with methemoglobinemia?
low SpO2 and normal PaO2
What causes the plateau of the oxygen dissociation curve after 75% saturation?
Haemoglobin molecule is already bound to 3 O2 molecules, the rate of reaction is slower to bind to the fourth.
What shape is the oxygen dissociation curve?
Sigmoid curve
When is the rate of O2-Hb dissociation the fastest and why?
Between 25-50% saturation, due to co-operative binding
What does a right-hand shift in the oxygen dissociation curve mean for affinity?
Hb has reduced affinity for O2. More O2 is unloaded to the tissues.
Acidosis, hypercapnia and hyperthermia are all reasons for what shift in the oxygen dissociation curve?
Right-hand shift
Alkaline pH, hypocapnia and hypothermia are all reasons for what shift in the oxygen dissociation curve?
Left-hand shift
What does a left-hand shift in the oxygen dissociation curve mean for affinity?
Hb has a higher affinity for O2. Less O2 is unloaded to the tissues.
Carbon-monoxide poisoning moves the oxygen dissociation curve which way?
Left-hand shift
Where is myoglobin found and why?
Cardiac muscle, it has a high affinity for oxygen so does not unload it easily, allows storage even at low partial pressures.
What percentage of CO2 is transported in the plasma?
9%
How is the majority of CO2 transported in the blood?
Undergoes a reaction with water to produce carbonic acid, which readily dissociates into H+ and HCO3-.
What is the chloride shift and why is it important?
HCO3- diffuses out of systemic circulation, Cl- diffuses into systemic circulation to maintain electrical balance
What maintains the pH of systemic circulation despite the protons produced by the dissociation of carbonic acid?
Deoxyhaemoglobin acts as a buffer, binding to H+.
What are the three main buffer systems?
Protein buffer system, phosphate buffer system and carbonic acid-bicarbonate buffer system
What is the most preferable buffer system and why?
Bicarbonate buffer system because of it’s abundance and easy regulation.
What is the main limitation of the bicarbonate buffer system?
Cannot protect against pH changes due to respiratory issues because it’s production is tightly regulated by CO2 abundance
Describe the relationship between pH, bicarbonate ion and carbon dioxide.
pH inversely proportional to CO2: if CO2 is high, pH is low and vice versa.
pH proportional to HCO3-: if HCO3- is low, pH is low and vice versa.
How does the metabolic system compensate for respiratory acidosis?
Increased excretion of protons, which increases the plasma level of bicarbonate ion (alkalotic substance)
How might gastric vomiting cause metabolic alkalosis?
Removal of HCl in stomach, decrease in protons in circulation.
What is a base excess?
Theoretical amount of acid needed to bring blood back to a normal pH.
