4 - Gas Transport and Exchange Flashcards
What are the following prefixes in nomenclature? P F S C Hb
P- partial pressure F - fraction S - Hb saturation C - content (mL) Hb - volume bound to Hb (mL)
name the 5 gas laws
- Dalton’s
- Fick’s
- Henry’s
- Boyle’s
- Charles’
what is Dalton’s law?
(partial pressures)
the partial pressure of gas in a mixture is equal to the sum of the partial pressure of gases in the mixture
What is Fick’s law?
(diffusion)
molecules diffuse from regions of high concentrations to low concentrations at a rate proportional to the concentration gradient, the exchange surface area and diffusion capacity of the gas, and inversely proportional to the thickness of the exchange surface
what is Henry’s Law?
(solubility)
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?
(gas and volume)
at a constant temp, the volume of a gas is inversely proportional to the pressure of that gas
what is Charles’ law?
(volume and temperature)
at a contant pressure, the volume of a gas is proportional to the temperature of that gas
what is the average PO2 in the repertory airways?
13.5 kPa
what is the structure of haemoglobin monomers?
have a ferrous iron ion (Fe2+) at the centre of the tetrapyyrole porphyrin ring, connected to a protein chain (globin), covalently bonded at the proximal histamine residue
What are the 4 chains in normal haemoglobin (HbA)?
2 alpha and 2 beta chains
what are the 4 chains in HbA2?
it has 2 alpha and 2 delta chains
NOTE: HbA2 is a normal variant of haemoglobin
it constitutes around 2% of all haemoglobin
what are the 4 chains in foetal haemoglobin?
2 alpha and 2 gamma chains
present in trace levels
Haemoglobin is allosteric. What does this mean?
The binding of oxygen to one of the subunits is affected by its interactions with the other subunits.
The binding of oxygen to one haemoglobin subunit induces conformational changes that are relayed to the other subunits, making them more able to bind oxygen by raising their affinity for this molecule.
Thus the binding of oxygen to haemoglobin is said to be cooperative.
As oxygen binds, what happens to the centre of the tetramer?
a conformational change occurs that makes the centre a binding site for 2,3-DPG (a glycolytic by-product)
When ATP is being produced in large amounts, what happens to the levels of 2,3-DPG?
it increases
therefore, its levels are reflective of the levels of metabolism
What effect does 2,3-DPG when it binds to the centre of haemoglobin?
it decreases the affinity of haemoglobin for oxygen i.e. promotes the unloading of oxygen.
When metabolism is higher, more oxygen unloading is required, 2,3-DPG will bind and ‘squeeze’ out the oxygen so there is more available for the repairing tissue
What is haemoglobin co-operativity?
the haemoglobin changes shape and affinity based on how much oxygen is bound
what kind of relationship does dissolved oxygen have with PO2?
linear (but very shallow): the greater the partial pressure of oxygen, the more oxygen is dissolved
What kind of shape is the oxygen dissociation curve?
sigmoid - this gives effectively 100% saturation across a big range of alveolar PO2.
Under what circumstances would the ODC shift right? (Bohr shift)
(promotes unloading of oxygen)
(decreased affinity for oxygen)
NOTE: all of these take place when you EXERCISE /increase energy consumption:
- increased temperature
- acidosis (due to increase in lactic acid and excess CO2)
- hypercapnia (elevated CO2 because there is more cellular metabolism)
- increased in 2,3-DPG
Under what circumstances would the ODC shift left?
(promotes loading of oxygen) (increased affinity for oxygen) NOTE: opposite effects of exercise - decreased temperature - alkalosis - hypocapnia - decreased 2,3-DPG
is the pH lower in the lungs of tissues?
lower in the tissues since this helps to facilitate unloading
Why would the ODC curve move up and down?
DOWN: - anaemia (lower Hb conc) (impaired oxygen carrying capacity) UP: -polycythaemia (increased conc of Hb in the blood) (increased oxygen-carrying capacity)
NOTE: saturation of the Hb still remains the same
polycythaemia- haematocrit (ratio of RBCs to plasma volume increases) so blood will get thicker and blood will flow slower, which will impede oxygen delivery
what effect does CO poisoning have on haemoglobin?
INCREASED AFFINITY
DECREASED CAPACITY
Hb has a much higher affinity for CO than O2, so if it binds, it will greatly decrease the amount of haemoglobin available for O2 to bind to.
NOTE: if 2 CO and 2 O2 are bound to a haemoglobin molecule, the haemoglobin will hold on to the oxygen tighter and be less willing to release it at respiring tissue
What effect doe CO have an the ODC?
downwards and leftwards shift
what is methaemoglobin?
What can it lead to?
when ferrous iron is oxidised to become its ferric form, by something other than O2
can lead to functional anaemia
what oxidises Hb into ferric MetHb?
Nitrites
How does foetal haemoglobin differ to normal Hb?
has high affinity since it takes oxygen from the mother’s blood
what is myoglobin and what does its ODC look like?
a monomeric protein NOT a haemoglobin variant
has an hyperbolic ODC
for explosive muscle actions
what is mixed venous blood?
‘deoxygenated blood’, when in fact it has around 75% oxygen bound
what is the PO2 of the mixed venous blood arriving at the exchange surface (alveoli)?
around 5.3 kPa
what are the 2 types of cells pneumocytes that line the alveoli?
- type I pneumocytes- flat, long and wide (good for diffusion). responsible for gas exchange
- type 2 pneumocytes (granular)- secrete surfactant
at the lungs, the blood is at 100% saturation. Why is it only at 97% saturation when it reaches the blood?
it becomes diluted by the bronchial circulation which drains back into the pulmonary circulation before returning to the left atrium
what is oxygen flux?
the overall amount of oxygen being deposited
how does the concentration of oxygen change at the tissues?
20.3 mL/dL—–> 15.1mL/dL
how does the saturation of oxygen change at the tissues?
97%—–> 75%
how many litres of blood in the body?
5
what is the resting volume of oxygen consumed per minute?
250 mL per minute
Is CO2 or O2 more likely to dissolves into the bloodstream?
carbon dioxide
how does CO2 dissolve into the blood?
- once in the plasma, it may react with any water present and turn into carbonic acid
- carbonic acid will then dissociate into HCO3- and H+ (bicarbonate and a proton). This is a very slow reaction because this reaction is non-enzymatic
- CO2 moves into RBCs, where there are enzymes.
- inside the RBC, bicarbonate is produced form CO2 at a rate that is 5000 times faster than in the plasma
- carbonic anhydrase is the enzyme in this reaction
after CO2 has dissociated into H+ and HCO3- inside the RBC, how is the bicarbonate ion moved out of the cell?
It diffuses out into the plasma via the AE1 TRANSPORTER and a chloride ion will move in
- an anion is being moved out so an anion is also brought in to maintain the chemical electroneutrality across the membrane
(the inwards movement of chloride is called the chloride shift)
- the movement of chloride into the cell draws water with it. When the bicarbonate moves out, water is essentially also being moved out, so if water didn’t move back in, the cell would dehydrate
how does CO2 bind to proteins in haemoglobin?
CO2 binds to the amine end of the proteins ofrming carbaminohaemoglobin (HbCO2)
How do RBCs maintain the concentration of H+ ions (from the dissociation of carbonic acid)?
the proteins make good buffers.
Some of them are negatively charged e.g. histidine and are good proton acceptors
overall, what are the 3 main roles of RBCs in CO2 transport?
1 - presence of carbonic anhydrase
2 - binding of CO2 at amine end of proteins
3 - buffering protons
(4 - also binds and carries nitric acid)
NOTE: when the blood reaches the lungs, the processes will reverse to unload CO2)
how is most of the CO2 carried in the blood? (which of these processes is the most common?)
majority of the CO2 in the blood is carried as bicarbonate in the plasma and RBCs
define pulmonary transit time
the amount of time that the blood is in contact with the pulmonary exchange surface
what is the pulmonary transit time in humans?
0.75 seconds
how long does it take for all gas exchange to occur (at rest)?
0.25 seconds
what does a CO2 distribution curve look like?
it is more linear than ODC
what is haldane effect?
describes how the amount of CO2 that binds to the amine end of haemaglobin protein chains changes depending on how much oxygen is bound (allosteric behaviour)
if you have 100% O2 saturation, we don’t want CO2 binding so CO2 does not bind immediately after the alveoli
when it gets to the tissue, oxygen starts to unload and the haemoglobin protein chains become more receptive to binding CO2
Blood flow to the lungs is not homogenous. Describe how and explain why.
The base of the lungs receives more perfusion and ventilation than the apex.
- it takes less effort to push through lower resistance circuit at the bottom because it isn’t pumping against gravity
- less blood perfuses the apex of the heart because of the resistance of gravity - blood will peripherall perfuse capillary beds at the base of the lung before the apex
- there are higher transmural pressure at the base
What does the graph of V/Q (ventilation/perfusion) from the base to the apex of the lung look like?
- ventilation and perfusion are both higher at the base and lower at the apex and have a linear relationship
- perfusion has a much steeper gradient than ventilation (this is because the density of blood is greater than that of air so gravity has more of an impact)
- V/Q - at the base, it tends towards 0. At the apex, it tends towards infinity.
Where the 2 lines cross, V/Q=1 and ventilation is equal to perfusion
Exercise shifts the ODC to the _____
right
