Gas transport Flashcards
What are the two main ways oxygen is carried in the blood?
- Dissolved in plasma
- Attached to haemoglobin
What is the amount of drug dissolved in plasma directly proportional to?
Partial pressure
What is haemoglobin made of?
- Haem - iron containing compound
- Globin - protein of 4 polypeptide chains
What causes the sigmoidal oxygen-haemoglobin dissociation curve?
- Positive co-operative binding - once first O2 is bound, the next three are easier to bind
What is the Oxygen saturation of haemoglobin at the tissues roughly?
75%
What percentage of bound oxygen is normally unloaded at the tissues?
25% - leaving a large reserve without needing to increase RR or CO
What does the flat upper plateau on the oxygen saturation curve result in?
Means that even if PO2 falls, saturation is not greatly altered, so at altitude O2 supply is still usually adequate
What is the PO2 of oxygen at the level of the tissues?
40mmHg
What factors shift the oxygen saturation curve to the right?
- Increased temperature
- H+
- CO2
- 2,3 - biphosphoglycerate
What does a shift to the right mean for haemoglobin?
- Modifies the 3-D structure of haemoglobin, decreasing its affinity for oxygen
What is the Bohr effect?
- Increased CO2 leads to an increase in H+ which weakens the HB-O2 interaction
Where does the curve shift to at the lungs?
Shifts to the left
What is the purpose of ‘warming up’ muscles before exercise?
Results in a shift to the right in the curve meaning the haemoglobin is better at releasing O2
What does an increase in CO2 result in?
A shift to the right meaning O2 is released more easily
How do you calculate total O2?
(Hb x capacity x %saturation) + amount dissolved
What is normal Hb concentration in the blood?
150g/L
What is the usually capacity of haemoglobin?
1.35ml/g Hb (usually lies between 1.35 and 1.39)
What is the usual arterial blood saturation?
98%
Why is arterial blood saturation only 98%
Bronchial arteries supply 2% of blood to lungs
What are the different methods of transport of CO2 in the blood?
- Dissolved in plasma
- Bound to haemoglobin
- As bicarbonate
What percentage of CO2 is disolved in plasma?
7 - 10%
What percentage of CO2 is bound to haemoglobin?
10 - 20% bind to the amino acids not the haem
What is loading and unloading of CO2 from haemoglobin directly related to?
- PCO2
- Degree of oxygenation of Hb
What is the haldane effect?
Deoxygenation of Hb increases its ability to bind CO2, (eg in the tissues) and vice versa in the lungs, oxygenation of Hb releases CO2 into plasma for transport into alveoli
What percentage of CO2 which is transported is in the form of bicarbonate?
70 - 80%
What is the unstable compound which CO2 produces when dissolved in water?
Carbonic acid
What enzyme present in RBC makes the CO2 conversion to carbonic acid very rapid?
CArbonic anhydrase
Write the chemical equation for CO2 when it enters the blood?
CO2 + H2O H2CO3 H+ + HCO3-
What is the chemical formula for carbonic acid?
H2CO3
What is the chemical formul for bicarbonate?
HCO3-
What chemical causes an electrical balance in the plasma?
Cl-
Where is the majority of bicarbonate produced?
Inside the RBC
What is the Henderson-Hasselbach equation?
pH = pK + (log[bicarbonate])/(CO2)
What is the pK value?
6.1
What is acidosis?
pH < 7.35
What is alkalosis?
pH > 7.45
