Gas Transport Flashcards
What are the 2 main gases involved in gas transport?
Oxygen and carbon dioxide
What are the 2 ways oxygen can be carried around the body?
- dissolved in plasma
- carriage by haemoglobin
What are the main characteristics of O2 dissolved in plasma?
- proprtional to partial pressure
- O2 is poorly soluble
How much oxygen does blood with a PO2 of 100mmHg contain?
0.3ml O2 /100ml blood
What is the most inefficient way to deliver oxygen around the body?
Oxygen dissolved in the plasma
What are the tissue requirements of oxygen for the body at rest?
250ml O2/min
What is meant by the terms haem and globin?
Haem = iron containing compound
Globin = protein of 4 polypeptide chains
What does oxygen and haemoglobin form?
easily reversible combination of oxyhaemoglobin
HbO2
How many binding sites does each haemoglobin have?
4
What does positive co-operative binding mean?
once the first O2 is bound, the next three bind easier
What does affinity of Hb for O2 change with?
increases with the extent of Hb saturation
What is the shape of the oxygen-haemoglobin dissociation curve?
sigmoidal
Describe the 5 main aspects of gas transport that relate to this curve
- In the lungs PO2 is high, so Hb is fully saturated
- At tissue level PO2 has fallen by more than half but the Hb is still saturated at 75% (PO2 doesn’t alter saturation)
- Flat upper plateau means that even when PO2 falls saturation is not greatly altered
- Steep lower part means that tissues can extract lots of O2 for a small drop in PO2
- 25% is normally unloaded at tissues, leaving a large reserve without needing to increase respiratory rate or cardiac output
How do an increase in:
- temperature
- H+
- CO2
- 2,3-bisphosphoglycerate
affect the oxygen-haemoglobin saturation curve?
Shift the curve to the right
How do an increase in:
- temperature
- H+
- CO2
- 2,3-bisphosphoglycerate
affect Hb’s affinity for O2?
All modify the 3D structure of Hb, decreasing affinity for oxygen hence the shift to the right
e.g. warmed muscles are better at releasing O2
How does CO2 affect Hb’s affinity for oxygen?
Increasing CO2 leads to an increase in H+ which weakens the Hb-O2 intertaction causing the Bohr-Effect to occur
Draw a diagram indicating how the oxygen-haemoglobin curve is altered by different biochemical factors
What equation is used to determine how much oxygen is carried in the blood?
Total = ([Hb] x capacity x % saturation) + amount dissolved
[Hb] = 15g/100ml
Capacity = 1.35ml O2/g Hb (range = 1.35-1.39)
% saturation = 98%
Amount dissolved = 0.3ml O2/L
Approx. 200ml O2/L
What are the 3 methods used to transport carbon dioxide in the body?
- Dissolved in plasma
- Bound to Hb
- As bicarbonate
What % of CO2 transported is dissolved in the plasma?
7-10%
Why is there more CO2 in the blood than O2
Carbon dioxide has greater solubility than oxygen, so this mechanism has more signficant effect in respiration overall
What % of carbon dioxide is transported by Hb in the blood?
10-20%
What is the compound formed when Hb binds with carbon dioxide?
carbaminohaemoglobin
Does carbon dioxide compete for the same sites on the Hb as oxygen?
NO
What is the loading and unloading of CO2 from Hb directly related to?
PCO2 and degree of Hb oxygenation
What is the Haldane effect?
deoxygenation of Hb increases its ability to bind CO2 and visa versa in the lungs, oxygenation of Hb releases CO2 into plasma for transport into alveoli
What percentage of CO2 is transported as bicarbonate?
70-80%
How is bicarbonate formed?
When CO2 dissolves in water it forms carbonic acid which is unstable so breaks down to form H+ and HCO3-
What speeds up the formation of bicarbonate?
prescense of carbonic anhydrase in RBC
How does H+ cause the Bohr shift?
Binds to Hb
How is the electrical balance maintained in RBC with an increase in H+?
chloride ions move in
Draw a diagram illustrating oxygen release and CO2 pickup and where does this occur?
tissues
Draw a diagram illustrating carbon dioxide release and oxygen pick up in the lungs
What impact does the transport of CO2 have on the blood?
major impact on pH
pH =
What is the normal pKa of the blood?
6.1
How is CO2 calculated?
according to solubility of the gas and partial pressure of CO2
Describe each of the lines in this diagram
- Line AB = plasma pH changes as CO2 changes
- if ventilation decreases, CO2 increases, pH falls and HCO3- - respiratory acidosis
- if the patient hyperventilates blowing off more CO2 this causes respiratory alkalosis
- Line CD = plasma pH changw when non-volatile acid is added/removed
- metabolic changes
When does acidosis occur?
pH < 7.35
When does alkalosis occur?
pH > 7.45
What is normal kPa in alveolar air for O2?
13.9
(104mmHg)
What is normal kPa in alveolar air for CO2?
5.3
(40mmHg)
