Week 4: Diffusion and Gas Transport Flashcards
what is boyles law
Pressure is inversely related to volume
An increase in pressure will result in a decrease in gas volume
what is henrys law
The amount of gas in a solution is proportional to the partial pressure of the gas
High pressure forces more gas into a solution
what is daltons law
Gases exert pressure that is proportional to their abundance
More gas = higher pressure
If we use nitrogen as an example, the air around us is made up of around 79% nitrogen. And as pressure is generated by the collision of particles, it is logically to assume that nitrogen makes up 79% of the total collisions. We can then assume, that nitrogen is responsible for generating 79% of the atmospheric pressure (At sea level or 760 mmHg, it would be responsible for 597 [using 78.6%])
What is ficks law (there are 3 aspects to Ficks law) and what is it formula therefore
If you increase the surface area of the lung, you will increase the rate of gas diffusion
If you decrease the thickness of the respiratory membrane, you will increase the rate of gas diffusion
If you increase the partial pressure difference across the respiratory membrane (P1-P2), you will increase the rate of gas diffusion (a higher driving gradient for diffusion)
V’ gas = (A*D*(P1-P2)) / T
Haemoglobin is a __ unit protein. One deoxyhaemogobin can bind __ molecules of O2.
100% saturation would mean __ oxygens are bound
50% saturation would mean __ out of the 4 oxygens are bound
When we average this across the millions of RBC’s in a patient this number can range anywhere between 1 and 100%
4, 4, 4, 2
what is the advantage of carrying O2 on Hb and not just in the blood
The advantage of carrying oxygen on the haemoglobin (Hb) and not just in the blood is that it maximises the pressure gradient from alveoli to the blood so as to achieve the highest level of diffusion of oxygen into the blood. When oxygen is bound to Hb it is effectively ‘invisible’ to the pressure gradient meaning even if the content of oxygen in the blood is higher, the diffusion gradient forces oxygen towards the blood
Explain how Hb maximises blood carrying capacity and pressure gradient.
When oxygen is bound to Hb it is effectively ‘invisible’ to the pressure gradient meaning even if the content of oxygen in the blood is higher, the diffusion gradient forces oxygen towards the blood
Basically we have maximised blood carrying capacity, by locking away oxygen onto the haemoglobin so that we allow more oxygen to diffuse into blood
Whereas if we did not have haemoglobin, like in picture A, you only have 8 oxygen in the blood and cannot get anymore as the partial pressure gradient has equalised, whereas when you have haemoglobin, like in picture C, you now have 14 oxygen in blood. The oxygen gradient has equalised as there are 2 loose oxygen and 2 oxygen in alveoli.
NOTE: Content refers to number of oxygen (bound and unbound), saturation refers to number of bound oxygens to Hb, dissolved oxygen refers to those that are free
Why is carbon monoxide poisoning lethal
binds to same site of Hb as O2. Therefore, further decreases O2 ability to difusse into blood. Also Hb has 200x more affinity to bind with Carbon monoxide
Explain the binding relationship between Hb and O2.
The relationship between partial pressure and saturation of haemoglobin is not linear. This can be explained by the increasing velocity constants that increase with each subsequent oxygen bound
That is, the first oxygen is the hardest and slowest to bind, the 4th oxygen is the easiest and fastest to bind – Hb
This is due to a conformational change in the proteins shape that shifts the Hb molecule from a tense state (T) (that has low oxygen affinity) to a relaxed state (that has a high oxygen affinity) (R). It is this fact that makes the non-linear relationship between partial pressure and saturation
Think of a slinky opening up
what is the plateu region in the oxygen-haemoglobin dissociation curve
Plateau Region (1)
Is the region that is close to flat that is also known as the loading zone (where oxygen binds to haemoglobin)
This region has a partial pressure of 100mmHg and a saturation of around 97.5%
A decrease in alveolar pressure leads to a decrease in arterial pressure (a drop in the overall oxygen partial pressure) but little change in oxygen saturation
If the oxygen partial pressure drops by 40 units to 60, this will only result in a decrease of oxygen saturation by about 10%, creating an excellent safety measure to maximise oxygen carriage in blood
what is the steep region in the oxygen-haemoglobin dissociation curve
Steep Region (2)
This region is known as the unloading region
Small drops in systemic capillary oxygen partial pressures will lead to large drops in oxygen saturation
The steep region is good for delivering oxygen to the tissues (a small drop in tissue oxygen partial pressure will cause a large drop in oxygen saturation of Hb. That is, more oxygen needs to be ripped of from the haemoglobin and delivered to the mitochondria of the muscle cells for use of energy)
Basically it gives this ‘loading’ and ‘unloading’ advantage. Where you can rip of oxygen from haemoglobin, deliver the oxygen to the tissues where needed (unloading)
Explain what a shift in the left would cause in the oxygen-haemoglobin dissociation curve
A shift to the left would favour the loading of oxygen
A shift to the left will increase the saturation, however as we are already at 97-98% saturation at the top of the curve, there is not a lot of gain to be made
Thus, only a minimal gain is achieved by shifting the curve to the left
Explain what a shift in the right would cause in the oxygen-haemoglobin dissociation curve
A shift to the right would favour the unloading of oxygen
If we consider normal oxygen partial pressure to be about 40 in the tissue, looking at the normal line (red) Hb saturation is at about 70
Once we shift the line to the right, Hb saturation at the same 40 is down to about 50
Thus, shifting the curve to the right unloads more oxygen to the tissues
What are 3 factors that would shift the oxygen-haemoglobin dissociation curve to the right
An increase in temperature
If I have a working muscle, it is going to increase in temperature which causes a shift to the right
This consequently increases the amount of oxygen unloaded at the tissue
An increase in DPG / BPG levels
DPG is synthesised as a product of the TCA cycle (as a result of glycolysis) which binds to the Hb beta chains, stabilising the tense state of Hb, reducing oxygen affinity
This shifts the curve to the right, decreasing saturation and unloading oxygen to the tissues
Increased partial pressure of carbon dioxide
This is known as the Bohr effect
Increase partial pressure of CO2 causes increased production of carbonic acid which breaks down to form increased numbers of H+
Increased acidity caused by the hydrogen ions reduces Hb affinity for oxygen by stabilising the Tense state
This encourages the unloading of oxygen at tissues
The opposite of these factors would result in a shift of the curve to the left (decrease in temp. decrease in DPG etc.)
An easy way to remember this is through thinking about exercise. An exercising muscle has a high demand for oxygen which is something it desperately needs to function. Thus, we need a shift to the right of the dissociation curve so that more oxygen is unloaded in the tissues. In order to achieve this, the following occurs;
It increases in temperature (muscles get hot when you exercise)
It becomes acidic (as a result of lactic acid)
Carbon dioxide levels rise (as a result of increased oxygen consumption)
It undergoes rapid glycolysis to gain energy (resulting in DPG)
These all individually right shift the curve, the opposite of these factors will favour loading (a left shit)
what is the bohr effect
- Increase partial pressure of CO2 causes increased production of carbonic acid which breaks down to form increased numbers of H+
- Increased acidity caused by the hydrogen ions reduces Hb affinity for oxygen by stabilising the Tense state
- This encourages the unloading of oxygen at tissues
what is the haldane effect
- The Haldane effect refers to the fact that a Hb that releases an Oxygen, binds a CO2 more easily than a Hb with an oxygen bound. So therefore, the act of releasing an oxygen means you can bind more CO2 (deoxygenated Haemoglonin binds more CO2 and hydrogen ions more easily than an oxygenated haemoglobin)
what is the chloride shift
when a tissue cell is working hard it forms Co2. This Co2 travels down its partial pressure gradient and enter the blood where it can a number of things. (dissolve into plasma, form bicarbonate (60-70% will) or bind to Hb.
If we don’t do anything the bicarbonate will build up and eventually stall the equation and therefore alter the partial pressure of CO2.
The body ensures this does not happen via the chloride shift which involves moving the bicarbonate ions that were formed by the CO2 out of the RBC in exchange for a Cl- ion
Explain at the alveoli to blood, how it favours diffusion of O2 into blood and CO2 out. (include how the bohr effect, haldene effect and one of ficks laws comes into play)
Ficks Law: because you have increase partial pressure of O2 in alevoli than in deoxygenated blood. Will favour of diffusion of O2 into blood. Have increase partial pressure of Co2 in deoxygentated blood (40) and less in alevoli, therefore, favour the diffusion of CO2 into alveoli.
Also have increase SA –> increase diffusion of O2
Bohr effect –> decrease CO2 envirionment will not stabilise tense state of Hb therefore will get increased loading of O2. –>maximise O2 carrying capacity by the blood.
Haldene effect –> unloading CO2 will increase affinity for binding of O2
Explain at the tissue cell to blood, how it favours diffusion of CO2 into blood and O2 out. (include how the bohr effect, haldene effect and one of ficks laws comes into play)
Ficks Law: because you have increase partial pressure of O2 in blood than in cell. Will favour of diffusion of O2 into cell. Have increase partial pressure of Co2 in cell (46) and less in blood, therefore, favour the diffusion of CO2 into blood.
This is where the chloride shift also comes into effect.
Bohr effect –> increase CO2 envirionment will stabilise tense state of Hb therefore will get increased unloading of O2. –>maximise O2 delivery to tissue
Haldene effect –> unloading O2 will increase affinity for binding of CO2
What is the Partial pressure of O2 and CO2 in atmospheric air
160 and 0.03
What is the Partial pressure of O2 and CO2 in alveoli
O2 = 100, CO2 = 40
What is the partial pressure from alveoli to blood for O2 and blood to alevoli for Co2.
what is the O2 partial pressure from blood to tissue and the CO2 partial pressure from tissue cell to blood?
Calculate the PO2 in dry inhaled air and in humidified air, assuming Pb = 760mmHg and water vapour pressure (Ph2O) = 47mmHg in humidifed air. What is the effect of the addition of water vapour?
PO2 dry air = 760 x 21% = 160
PO2 of humidified air = (760 - 47) x21% = 149.02
Therefore the water vapour lowes the Partial pressure of O2 but we need this water as dry air damages the airways.
Calculate the partial pressure of 21% oxygen in air at sea level and at the summit of Mt Everest(assuming PB=253Hg). What are the implications of high altitude (low Pb) on oxygen diffusion and at lung and delivery to the cells?
0.21 x 253 = 53.13
You have a decrease PO2. THis means you will breath in less O2 and have less O2 diffuse into the blood. You will have less oxygen difussion from alveoli to blood and from blood to tissue due to decreased PO2.
Calculate the partial pressure of 79% nitrogen in air at sea level and at a depth of 30m (assuming PB = 4 atmospheres = 3040mmHg)
3040 /4 = 760
- 79 x 760 = 600.4
- 79 x 3040 = 2401.6mmHg
If oxygen and carbon dioxide were both present in the same concentration in a solution, how would there partial pressures compare?
CO2 would have lower pp as it is 20x more soluble than O2. therefore more of it in solution
How does the positive cooperativity of oxygen binding with haemoglobin assist in unbinding O2?
the cooperativity of O2 binding means it is easier for the 1st O2 molecules to dissociate from Hb.
Could a human survive without Hb in the blood?
No - as the PO2 gradient would decrease and then less O2 diffusing into blood –> decrase O2 avalible for tissue
