4 Gas Transport Flashcards
Q: What do these symbols mean?
P, S, A, a
A: partial pressure
Hb saturation
alveolar
arterial
Q: What are the 5 gas laws?
A: -dalton’s
- fick’s
- henry’s
- boyle’s
- charle’s
Q: What’s Dalton’s Law?
A: partial pressure of a gas mixture is equal to the SUM of the partial pressures of gases in the mixture
Q: What’s Fick’s Law? Equation?
A: molecules diffuse from regions of high concentration to low concentration 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
A
– x D x [P(1)-P(2)]
T
Q: What’s Henry’s Law? Meaning? Equation?
A: 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
i.e. bigger solubility coefficient = will dissolve more easily
C (D Gas)= a(Gas) x P(Gas)
Q: What’s Boyle’s Law? Equation?
A: at a constant temperature, VOLUME IS INVERSELY PROPORTIONAL TO PRESSURE
P(Gas) ∝ 1
—
V(Gas)
Q: What’s Charle’s Law? Equation?
A: at a constant pressure, VOLUME IS DIRECTLY PROPORTIONAL TO TEMPERATURE
V(Gas) ∝ T(Gas)
Q: What is involved in giving someone oxygen therapy? Reason. Show using diagram.
A: supplement the amount of oxygen in the air
As the patient has a diffusion problem, you need to make the diffusion gradient steeper
10 by 10 square. 40 are nitrogen, 59 are oxygen, last square is argon, co2 and others
Q: Show using a diagram what is in room air. (5)
A: 78 are nitrogen, 21 are oxygen
0.9 of a square=Argon
CO2= 0.04
random others
Q: What does having higher altitude mean? (2) Show on diagram.
A: pressure of atmosphere decreases but the PROPORTIONS OF THE GASES REMAINS THE SAME
same as room air proportions but boxes are smaller= smaller volumes
Q: What’s the partial pressure of oxygen, carbon dioxide and water in dry air (at sea level)? How does this change once in the conducting airways? How does this change once in respiratory airways?
A: 21.3kPa
0kPa (effectively when rounded)
0kPa
20kPa (as mixed with air already in there)
0kPa
6.3kPa (becomes saturated as gets warmed, humidified, slowed and mixed as it passes down the respiratory tree)
- 5kPa (100% saturation)
- 3kPa (due to gas exchange)
- 3kPa
Q: Why is it good that we make dry air saturated?
A: protects airways, improves conductivity
Q: How much oxygen can you dissolve in your body? What rate? What is the resting volume of oxygen to keep our body running? Therefore?
A: 16mL, 0.32mL/min
250mL/min (oxygen consumption)
inadequate to support life -> can’t rely solely on dissolved oxygen to keep us alive
Q: What is the structure of haemoglobin? represented? What is the structure of Hb monomers? (4) ability to?
A: tetramer which 2 alpha and 2 beta chains - this is normal haemoglobin and is represented as HbA
ferrous iron ion (Fe2+) at the centre of the tetrapyrrole porphyrin ring connected to a protein chain (globin), covalently bonded at the proximal histamine residue
->Each haem binds ONE molecule of oxygen
Q: Describe a normal variant of Hb. Contributes to what percentage of all haemoglobin? Structure of foetal Hb? presence?
A: HbA2 - this has 2 alpha and 2 delta chains - this constitutes about 2%
HbF= present in trace levels and consists of 2 alpha and 2 gamma chains
Q: The genes responsible for coding the globin chain of Hb can produce how many variants? What are they?
A: 4= alpha, beta, delta, gamma
Q: When Hb is not bound to any oxygen, what is its oxygen affinity? What happens when oxygen does bind? causes? result?
A: low
conformational change where the structure relaxes and gets a greater affinity for oxygen - then more and more oxygen will bind
Q: How does the middle of a Hb molecule change when a conformational change occurs?
A: middle = made a binding site for 2,3-DPG - this is a glycolytic by-product
Q: What happens when ATP is produced in large amounts? reflective of? What can this substance do?
A: more 2,3-DPG is produced so it is reflective of metabolism
2,3-DPG DECREASES the affinity of haemoglobin for oxygen
A: What do you want when metabolism is higher? therefore? result?
A: more oxygen
so the 2,3-DPG will bind to the haemoglobin and squeeze OUT the oxygen so there is more available for the respiring tissue
Q: Why is Hb allosteric?
A: it will change shape depending on what is bound or not bound
Q: Describe the party analogy of Hb. (4) What is this called?
A: Haemoglobin is a party and oxygen is people
If there is no one at the party, then you wont want to go
As the party becomes bigger, everyone wants to go
A lot of people are wanting to be the last people to arrive at this really good party
This is called COOPERATIVITY - it will change its shape and affinity based on how much oxygen is bound
Q: What is MetHb? How is it produced? What can cause this? Oxygen binding? can cause? (2) Abundance?
A: methaemoglobin
if the ferous iron (Fe2+) is oxidised to its ferric form (Fe3+)
-nitrates can oxidise Hb
does not bind to oxygen and methaemoglobinaemia can cause functional anaemia (impaired oxygen capacity)
present in small amounts
Q: What would happen if the oxygen dissociation curve for Hb was linear? Draw a graph and explain (2). How does normal physiological range for PaO2 in the lungs change with age?
A: get a large variation in oxygenation in the lungs
There is a similar situation in the tissues - there is very little scope for increasing unloading
normal physiological range for PaO2 in the lungs decreases as you get older
Q: What’s the shape of the Hb oxygen dissociation curve? Draw it and explain why this is good. (2) Change?
A: sigmoid
This gives us effectively 100% saturation across a big range of alveolar PO2
In the tissues you can go from around 76% to 8% saturated - so there is very high unloading capacity
This ODC changes under different circumstances
Q: What can cause right shift of the ODC? example. What are the changes that take place with this example? (4) What happens in terms of oxygen affinity?
A: The curve can be shifted to the RIGHT by things that reflect higher energy consumption such as EXERCISE
When you exercise the following changes take place:
- Increase in temperature
- Acidosis (due to production of lactic acid and excess CO2)
- Hypercapnia (elevated CO2 because there is more cellular metabolism)
- Increase in 2,3-DPG
increased= more loading onto Hb
Q: What happens to oxygen affinity when the ODC shifts left? What can cause this? (4)
A: decreased= more unloading
opposite of the responses to exercise take place:
- Decrease in temperature
- Alkalosis
- Hypocapnia
- Decrease in 2,3-DPG
Q: How does pH differ in lungs and tissue? why?
A: the pH is lower in the tissues than in the lungs which helps it unload
A: What is the P50? How can this be calculated from the ODC? What is this value of pO2 a good indicator of? explain with example graph.
A: partial pressure of oxygen when haemoglobin is 50% saturated
drawing a line across at 50% saturation
P50 is a good indicator of the general shape of the ODC
In this example, if it is more or less than the normal value of 3.3 kPa pO2 then we can see how the curve is changing
Q: What happens when the ODC is ‘squished’? Why is this important? Therefore?
A: have a new total oxygen in blood concentration (20 to 15mL/dL)
can measure oxygen saturation of Hb with pulse oximetry and if it says 100% you may assume that patient is healthy but what if you have low Hb (concentration) and therefore overall reduced amount of oxygen in blood
Hb and oxygen saturation need to be considered together
Q: What can cause downwards shift of ODC? What can cause upwards shift? caused by? result? Why is this bad?
A: anaemia=less Hb=impaired oxygen carrying capacity
Polycythaemia = an increase in the packed cell volume (haematocrit) in the blood - it could be due to an increase in the number of red blood cells
As you have more red blood cells, your oxygen carrying capacity increases
You haematocrit (ratio of red blood cells to plasma volume will increase) so your blood will get thicker and the blood will flow slower which will impede oxygen delivery
Q: What can cause downwards and leftwards shift of the ODC?
A: carbon monoxide poisoning
Q: How does Hb affinity to CO and O2 vary? What does Hb binding to CO do? What happens if two of the chains in haemoglobin are bound to CO and the other two are bound to oxygen? Overall effect of CO? (2) Effect on ODC?
A: Hb has a much greater affinity for carbon monoxide than oxygen
reduce the amount of haemoglobin available to bind to oxygen
the two that are bound to oxygen will hold on to the oxygen tighter and will be less willing to release the oxygen at respiring tissue
- Increase Affinity
- Decrease Capacity
Downward and Leftward Shift
Q: Describe foetal Hb O2 affinity. How does the ODC change?
A: high affinity because it needs to ‘extract’ oxygen from the mother’s blood in placenta
left shift
Q: What is myoglobin? What is its ODC? Use and found where?
A: NOT a haemoglobin variant, myoglobin is a monomeric protein which has a hyperbolic ODC (almost a corner with a slight curve)
It is a protein in muscle which holds on to oxygen - it is there for a rainy day when the muscle needs oxygen rapidly
Q: What type of blood arrives at the gas exchange membrane? (2) How much oxygen is bound? pO2?
A: The blood that’s arriving is NOT deoxygenated, it is mixed venous blood
around 75% oxygen bound, PO2 of around 5.3 kPa
Q: At the gas exchange surface, what is in the alveolus? what does it do?
A: There is lots of oxygen in the alveolus which will diffuse through the exchange surface into the blood
Q: Describe the gradient at the gas exchange membrane between the vessel contents and RBC. What happens?
A: diffusion gradient in the red cell
The plasma concentration of oxygen is higher than the intraerythrocytic partial pressure so the oxygen will move into the red cell
When the oxygen moves in it will occupy the final binding spot in the haemoglobin and the haemoglobin will be 100% saturated
Q: How saturated is blood when it reaches the tissues? What changes take place? (2) What is the overall amount of oxygen being deposited? called?
A: 97%- goes down a little as it has been diluted- bronchial circulation drains into pulmonary vein before it enters the left atrium
Concentration of Oxygen:
-20.3 -> 15.1 mL/dL
Saturation of Oxygen:
-97 -> 75%
5mL/dL, oxygen flux
Q: What is the pulmonary/lung circulation made of?
A: two circulations - it has it’s own blood supply (bronchial) to keep it alive and it has the pulmonary blood supply for oxygenation of blood
Q: What is the overall amount of oxygen being deposited into tissues per dL? Overall? Resting volume of oxygen consumed?
A: 5mL/dL
There are 50 decilitres in the body so 5 x 50 = 250
REMEMBER: 1 DECILITRE = 100 MILLILITRES
250 mL of oxygen per minute
Q: How does CO2 transport occur at tissues? How does CO2 differ to O2? hence?
A: Carbon dioxide will diffuse into the blood stream
Carbon dioxide is much more soluble than oxygen so it dissolves in the plasma more happily
Q: Once the CO2 is in plasma, what may happen? Then? speed?
A: CO2 might bump into some water and it will turn into Carbonic Acid (H2CO3)
Carbonic acid then dissociates into a proton and bicarbonate (HCO3-) - this is a VERY SLOW reaction because there aren’t any enzymes
Q: Apart from dissolving in water, what can happen to CO2 when it enters blood? (2) Therefore RBC have?
A: moves into the red blood cells where there are enzymes (CARBONIC ANHYDRASE catalyses this reaction) -> bicarbonate is produced from carbon dioxide at a rate 5000 times greater than in the plasma
have major role in moving CO2
Q: What happens the bicarbonate produced in RBC? via? Explain. Called? Side effect? reason?
A: bicarbonate will diffuse out into the plasma via the AE1 transporter and a chloride ion will move in
Because an anion is moving out (HCO3-), we need to bring an anion in to maintain chemical electroneutrality across the membrane
This inwards movement of chloride via the AE1 transporter is called the CHLORIDE SHIFT
The movement of chloride into the red blood cell draws water with it
-Water was being used to react with carbon dioxide and it, in effect, moves out because half of the water is in bicarbonate so if water didn’t move in with chloride, the cell would dehydrate and get smaller
Q: What can CO2 bind to in RBC? how? to form?
A: proteins
Carbon dioxide will bind to the amine end of the proteins forming CARBAMINOHAEMOGLOBIN (HbCO2)
Q: What happens if the concentration of proton increases inside the red blood cells? Therefore? Example.
A: pH will decrease in RBC
We need to mop up these excess protons and the proteins make good buffers
-Some of the amino acids are negatively charged and are really good proton acceptors - histidine is particularly good
Q: When you get to the lungs, what occurs in terms of CO2 transport?
A: When you get to the lungs, the processes will reverse to unload CO2
Q: What are the figures for CO2 flux? Every minute?
A: goes from 52 - 48 mL/dL - +4 mL/dL net increase in CO2 concentration
200 mL of CO2 is produced every minute
Q: How does oxygen consumption and CO2 production compare? reason?
A: Oxygen consumption (250 mL) and CO2 production (200 mL) are not equal
This is because some of the water is lost in metabolic water production
Q: What is the respiratory membrane? role? Reason?
A: areas where the alveolar cells and endothelial cells of the capillaries are close enough for exchange to take place - gas exchange doesn’t take place until it reaches it
rate of diffusion is inversely proportional to thickness so only when the membranes are close enough will exchange take place
Q: Quantify the pulmonary transit time. What does this mean? What occurs a third of the way? condition?
A: around 0.75 s
the blood cells are only in contact with the respiratory membrane for this short time
By 0.25 s, all of the gas exchange is complete (at rest)
Q: When exercising, cardiac output increases and pulmonary blood flow increases. What else happens? (2) Could? However? How does CO2 and O2 compare?
A: -better access to some under perfused capillary beds
- blood may be too fast and not allow full gas exchange
- > could lead to hypoxaemia
there is still time to reoxygenate the blood
CO2 is much more willing to cross through the membranes so it exchanges much faster
Q: How does the CO2 DC differ to ODC?
What does it show about the change in pre-capillary aortic blood and post-capillary venular blood?
A: lot more linear than sigmoid shaped one
as blood goes past and oxygen is lost
Hb chains carry more O2
relationship between if there’s less O2, more CO2 will bind
if O2 is 100% saturated CO2 will not bind at amine end
more allosteric behaviour
Q: What is the haldane effect? Explain. (2)
A: describes how the amount of carbon dioxide that binds to the amine end of the haemoglobin protein chains changes depending on how much oxygen is bound - this is another allosteric behaviour
- Usually when the oxygen saturation is 100% (immediately after the alveoli) we don’t want to be binding CO2 and so at this point, carbon dioxide will not bind to the amine end of the proteins
- When we get to the tissues we start unloading oxygen and the protein chains on the haemoglobin become more receptive to binding CO2
Q: What is the blood flow to the lung not? explain. Therefore? Regarding alveoli.
A: NOT homogenous
It takes less effort for the heart to push through the lower resistance circuit at the bottom because it isn’t pumping against gravity
Less blood perfuses the apex of the lung because of the RESISTANCE OF GRAVITY
there is a similar relationship - there is better ventilation at the BOTTOM compared to the top
Q: How do areas of the lung vary in terms of perfusion? Ratio? (2)
A: base of the lung gets a lot more perfusion and ventilation
There are different ratios of ventilation to perfusion in different parts of the lung
Differences in V/Q:
- Base - tend towards ZERO
- Apex - tend towards INFINITY
Q: Describe the 3 zones of the lung that result from the differences in V/Q. Represent on graph.
A: Zone 1: Alveolar Pressure > Arterial Pressure > Venous Pressure
Zone 2: Arterial Pressure > Alveolar Pressure > Venous Pressure
Zone 3: Arterial Pressure > Venous Pressure > Alveolar Pressure
REFER
- ventilation
- perfusion
- V/Q (exponential)
- X: base–>apex
Q: How does arterial pressure vary to venous pressure? reason.
A: arterial pressure will always be greater than venous pressure or the blood would flow backwards
Q: Which of the following factors displaces the ODC to the right:
Decrease 2,3-DPG production
Hypocapnia
Hyperthermia
Alkalaemia
A: Hyperthermia
Q: Which of the following displaces the ODC to the right?
Increasing [H+]
Hyperventilation
Anaemia
Exercise
A: Hyperventilation – increase alveolar ventilation and bring down your CO2
Q: How much oxygen can 1g of haemoglobin bind?
- 003 mL
- 34
17
250
A: if normal Hb is 150g/L and 100% saturation is 20mL of oxygen per dL of blood
200/150= 1.33 mL
so closest is 1.34
