3. Gas Transport and Exchange Flashcards
What is Dalton’s Law?
Partial pressure of a gas mixture is equal to the sum of the partial pressures of gases in the mixture
What is Fick’s law?
Molecules diffuse from regions of high conc to regions of low conc at a rate proportional to the concentration gradient, the exchange surface area and the diffusion capacity of the gas, and inversely proportional to the thickness of the exchange surface
What is Henry’s Law?
At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid
What is Boyle’s Law?
At a constant temperature, volume is inversely proportional to pressure
What is Charle’s Law?
At a constant pressure, volume is directly proportional to temperature
If the patient has a diffusion problem what must be done?
Oxygen therapy: Increase the oxygen given - essentially making the diffusion gradient steeper
With altitude what happens with the gases?
The pressure of the atmosphere decreases but the proportions of the gases remains the same
How many kPa of oxygen is in dry air?
21.3 kPa
From dry air through the conducting airways how does the air change?
There is a slight reduction in pO2 and increase in pH20
How many kPa of of oxygen is in the conducting airways?
20 kPa
How many kPa of H2O is in the conducting airways?
6.3 kPa
Why is there an increase in the kPa H2O?
Because dry air becomes warmed, humidified, slowed and mixed as it passes down the respiratory tree
How many kPa of oxygen is in the respiratory airways?
13.5 kPa - this is 100% saturation
What is the solubility of oxygen?
You can only dissolve 17 mL of oxygen in your body at 0.34 mL/dL
What is the human oxygen consumption at rest?
250 mL/min
What is the structure of haemoglobin?
Tetramer - 2 alpha and 2 beta chains, represented as HbA. Each chain has as a ferrous iron ion (Fe2+) which binds 1 molecule of O2.
What chains are in HbA2?
2 alpha and 2 delta chains
How many percent of haemoglobin does HbA2 make up?
2%
What chains are in foetal haemoglobin (HbF)?
2 alpha chains and 2 gamma chain
Describe the affinity to oxygen for haemoglobin?
Sigmoid shape - When there is no oxygen bound there is a low affinity. However when the first oxygen binds there is a conformational change increasing its affinity to oxygen.
When oxygen binds to haemoglobin how does the middle change?
It becomes a binding site for 2,3-DPG
What is 2,3-DPG a measure of?
It is reflective of metabolism. The more ATP produced the more 2,3-DPG produced
What is the function of 2,3-DPG?
It is used to squeeze out the oxygen - decreases haemoglobins affinity for oxygen.
Define allosteric
It will change shape depending on what is bound or not bound
Define cooperativity
It will change its shape and affinity based on how much oxygen is bound
What does a high partial pressure of oxygen mean?
It means more oxygen will be dissolved
What is shape of the oxygen dissociation curve?
sigmoid curve
What is the oxygen saturation of haemoglobin in alveolar PO2/pulmonary system?
It is effectively 100% across a big range of PO2
What is the oxygen saturation of haemoglobin in the tissues/systemic system?
In the tissues it can go from 76% to 7% saturated - high unloading capacity
Define P50
The partial pressure of oxygen when haemoglobin is 50% saturated
What is P50 good at estimating?
The shape of ODC
What is the meaning behind an oxygen dissociation curve shifted to the right?
This suggests exercise - decreased affinity to oxygen so increased unloading
What happens when you exercise?
1) Increase in temperature
2) Acidosis (due to production of lactic acid and excess CO2)
3) Hypercapnia
4) Increase in 2,3-DPG
Define hypercapnia
Elevated CO2 because there is more cellular metabolism
What are the responses when the ODC shifts to the left?
Opposite of when it shifts to the right
What situation would cause the ODC shift downwards?
Anaemic - there is just a lower haemoglobin concentration hence lower amount of oxygen in the blood. However the saturation is the same
Less haemoglobin =
Lower oxygen carrying capacity
Define polycythaemia
increase in the packed cell volume (haematocrit) in the blood - it could be due to an increase in the number of RBC
What situation would cause the ODC shift upwards?
Polycythaemia - increased oxygen carrying capacity
What affect does CO have on the ODC?
Downards and leftwards shift
What does CO do to haemoglobin?
It decreases haemoglobin’s capacity for oxygen and increases its affinity.
How does CO increase haemoglobins affinity for oxygen?
When two of the chains are bound to O2 and the two are bound CO, The two chains bound to O2 will hold the oxygen more tightly
What is myoglobin’s effect towards O2?
It has a much greater affinity than adult HbA.
What is the function of myoglobin?
It extracts oxygen circulating in the blood and stores it
What is the function of foetal haemoglobin?
It has a high affinity so it can steal oxygen from the mother’s blood
What the shape of myoglobins ODC?
hyperbolic
What it the percentage of oxygen saturation arriving at the alveoli?
The blood arriving is 75% oxygen bound - not deoxygenated
What is the kPa of O2 arriving at the exchange surface of the alveoli in the mixed venous blood?
5.3 kPa
How does oxygen move from the blood into the RBC?
By diffusion. The plasma conc of oxygen is higher than the intraerthrocytic partial pressure of O2
What is the percentage saturation of blood when it reaches the tissues?
97%
Why is percentage saturation of blood not 100% by the time it reaches the tissues from the lungs?
It is diluted by bronchial circulation
How many circulations does the pulmonary system have?
2
What changes take place at the tissue?
The concentration of oxygen decreases from 20.3 - 15.1 mL/dL
The saturation of oxygen decreases from 97% to 75%
Define oxygen flux
The overall amount of oxygen being deposited
What is the oxygen flux in the tissues?
-5 mL/dL this is the amount of oxygen deposited at the tissues
How many decilitres are in the body?
50 dL
What is the resting volume of oxygen consumed?
250 mL of oxygen per minute
Where does CO2 diffuse into?
The blood stream
How soluble is CO2?
It is more soluble than O2
What does CO2 react with in the blood?
Water to form carbonic acid H2CO3
What does carbonic acid produced in the blood dissociate into?
H+ and HCO3-
This is slow reaction - no enzymes
What catalyses the reaction converting CO2 to H2CO3 in RBC?
Carbonic anhydrase
How many times faster does the enzyme in RBC catalyse the reaction?
5000 times greater
How does bicarbonate produced in the RBC leave and go into the plasma?
Via AE1 transporters which moves a chloride ion in
What is chloride shift?
The movement of Cl- into the RBC while exchanging for HCO3-. Electroneutrality must be maintained across the membrane
What does the Cl- ion bring with it when it moves into the RBC?
Water, which prevents the cell from dehydrating and getting smaller
How/where does carbaminohaemoglobin form?
When CO2 binds to the amino end of proteins.
How does pH within the RBC maintained with the production of H+ ions?
The proteins make good bufffers
How does the CO2 flux change from arterial and venous blood?
48 to 52mL/dL
How many ml of CO2 is produced every minute?
200 mL
How many ml of oxygen is consumed ever minute?
250mL
Define respiratory membrane
areas where the alveolar cells and endothelial cells of the capillaries are close enough for exchange to take place
Define pulmonary transit time
This is time where gas exchange can takes place
How long is the pulmonary transit time?
0.75s however gas exchange will already been completed in 0.25s
Define Haldane effect
Describes the amount of CO2 that binds to the amine end of the haemoglobin protein changes depending on how much oxygen is bound. Allosteric effect.
Will CO2 bind to haemoglobin when O2 saturation is 100%?
No, when it starts to unload O2 it becomes more receptive to CO2
Which part of the lung is least perfused and why?
The apex because of the resistance of gravity
Which part of the lung is better ventilated?
Bottom of the lung compared to the top
