Gas transport+ exchange

Question 1

Key gas laws

Answer 1

Dalton- Pressure of a gas mixture = sum (Σ) of partial pressures (P) of gases in that mixture
𝑷( 𝑮𝒂𝒔 𝒎𝒊𝒙𝒕𝒖𝒓𝒆)= ∑(P(𝑮𝒂𝒔𝟏 )+P(𝑮𝒂𝒔2 )+ P(𝑮𝒂𝒔n)

Fick- Molecules diffuse from regions of high concentration to low concentration at a rate proportional to the concentration gradient (P1-P2), the exchange surface area (A) and the diffusion capacity (D) of the gas, and inversely proportional to the thickness of the exchange surface (T)
V Gas= (𝑨/𝑻) x 𝑫 x [𝑷𝟏−𝑷𝟐]

Henry-At a constant temperature, amount of a given gas that dissolves in a given type and volume of liquid= directly proportional to the partial pressure of that gas in equilibrium with that liquid
𝑪( 𝑫 𝑮𝒂𝒔)=𝒂(𝑮𝒂𝒔) x 𝑷(𝑮𝒂𝒔)

Boyle- At a constant temperature, volume of a gas is inversely proportional to the pressure of that gas
𝑷(𝑮𝒂𝒔)∝ 𝟏/𝑽(𝑮𝒂𝒔)

Charles-At a constant pressure, volume of a gas is proportional to the temperature of that gas
𝑽(𝑮𝒂𝒔)∝ 𝑻(𝑮𝒂𝒔)

Question 2

Normal inspiratory gases %s
Changes in inspiratory gases when:
Oxygen therapy
Smoke (house fire)
High-altitude

Answer 2

78% N2, 21% O2, 1% Ar, 0.04% CO2, <0.01% others
O2 therapy= Increased O2 instead of N2
Smoke= decreased O2 (fire consumes O2), increased CO2, increased CO
Altitude= Less of everything but same proportions

Question 3

What happens to air as it passes down to alveoli

CO2 at alveoli?

Answer 3

Warmed
Humidified
Slowed
Mixed

CO2= higher conc at alveoli than in airways because diffuses up until gets to air flow where physical force moves it out

Question 4

O2 dissolved at rest
How to calculate?’
Value at rest? Units?
Implication?

Answer 4

Henry’s Law
16mL/ min
Need Hb to aid with oxygen delivery

Question 5

Hb monomer structure

Answer 5

Ferrous iron ion (Fe2+; haem- ) at centre of a tetrapyyrole porphyrin ring connected to a protein chain (globin)
Covalently bonded at the proximal histamine residue

Question 6

Types of Hb+ monomers

How are different monomers produced?

Answer 6

HbA= 2 Hbα+ 2 Hbβ
HbA₂= 2 Hbα+ 2 Hbδ
HbF= 2 Hbα+ 2Hbγ

Different genes for each monomer

Question 7

Affinity of Hb- name of process?

After 4th O2?

Answer 7

1st= low affinity= difficult+ slow
2+ 3= easier
4th= high affinity but also harder for it get in right place
Called cooperative binding

Allosteric behaviour: After 4th O2, 5th binding site for 2,3- DPG: pushes Hb into a more tense state (tightens up): causes some O2 to be ejected out

Question 8

Methaemoglobin
Redox pathways?
(slide 18, lecture 4)

Proportion of Hb?
Difference vs normal Hb?
Disease associated with this?

Answer 8

Small
Has an Fe3+ instead of Fe2+ which doesn’t bind to O2
Exists in equilibrium so redox pathways mean that Hb is constantly changing to MetHb
If the ratios change then you get methaemoglinaemia.

Question 9

Effect of ageing on o2 dissociation curve?

Answer 9

Shifts to left

Question 10

Normal O2 dissociation curve?
(slide 21, lecture 4)
Signficance of initial steeper part?
How to track changes in curve shape?

Answer 10

Able to take more O2 out of what is there

Use 50% Hb saturation point

Question 11

Rightwards shift of O2 dissociation curve

Leads to what?

Answer 11

Related to metabolic activity
↑ Temperature (metabolic activity= exothermic)
Acidosis (lower pH because higher CO2)
Hypercapnia (high CO2)
↑ 2,3-DPG

Question 12

Leftwards shift of O2 dissociation curve

Leads to what?

Answer 12

Promote unloading- for any given partial pressure, less O2 unbound
↓ Temperature
Alkalosis
Hypocapnia
↓ 2,3-DPG

Question 13

Upwards shift of O2 dissociation curve

Leads to what?

Answer 13

Polycythaemia (too much Hb in blood)
Increased oxygen-carrying capacity
HbO2 SATURATION AXIS= MOVES UP WITH THE SHIFT (Proportions are same) (Total O2 in blood axis same)

Question 14

Downwards shift of O2 dissociation curve

Leads to what?

Answer 14

Anaemia (not enough Hb in blood)
Impaired oxygen-carrying capacity
HbO2 SATURATION AXIS= MOVES DOWN WITH THE SHIFT (Proportions are same) (Total O2 in blood axis same)

Question 15

CO dissociation curve in relation to normal O2 dissociation curve- draw
(slide 24, lecture 4)

Effect of CO poisoning?

Answer 15

Downwards and leftwards shift

Decreased capacity for O2 carriage
Increased affinity
↑HbCO
Lower tissue based capacity for release

HbO2 SATURATION AXIS= MOVES DOWN WITH THE SHIFT (Proportions are same) (Total O2 in blood axis same)

Question 16

Foetal Hb+ Myoglobin O2 dissociation curve draw
(slide 25, lecture 4)

Foetal Hb explanation
Myoglobin explanation

Answer 16

Greater affinity than adult HbA for oxygen to take O2 from mothers blood in placenta

Greater affinity than adult HbA for O2 to take oxygen from circulating blood and store it. (used in sprinting/ early energy production)

Question 17

Saturation of Hb when it returns to alveolar

Answer 17

75%

Question 18

HbO2

Units?

Answer 18

How much O2 bound to Hb

mL/ dL

Question 19

C(D)O2

Units?

Answer 19

Dissolved content

mL/ dL

Question 20

C(a)O2

Units?

Answer 20

Arteriole oxygen content

mL/ dL

Question 21

Change in blood arriving to tissue than from lung

Answer 21

Lower O2 because bronchial tissue requires O2 too

Most drains into RA but some drains to vena cava= haemodilution

Question 22

Change of these things during blood transport to tissues:
O2 partial pressure
Saturation
HbO2
C(D)O2
C(a)O2

Answer 22

Large decrease
Less of a decrease than Partial pressure because of sigmoidal shape of O2 dissociation curve
Decrease
Decrease
Decrease

Question 23

Oxygen flux calculation

Units?

Answer 23

Oxygen flux= CO x ΔHbO2 (before tissue to after tissue exposure)
CO= 5L/ min but multiply by 50 because HbO2= dL
mL O2/min

Question 24

CO2 transport

Answer 24

1. CO2 leaves tissue into blood plasma
2. Combines with H20 in reversible reaction in plasma:
   CO2+ H2O ⇌ H2CO3
   Forward reaction= non-enzymatic
   H2CO3⇌ H+ + HCO3-
3. CO2 also enters RBC
   CO2+ H2O ⇌ H2CO3
   Forward reaction= carbonic anhydrase= increased rate of reaction
   H2CO3⇌ H+ + HCO3-
4. Chloride Shift= HCO3- swapped for Cl- outside RBC to maintain resting membrane potential through AE1 transporter
5. H2O enters RBC through membrane
6. CO2 also binds to Hb to form carboxyhaemoglobin at a different place from where O2 normally binds
7. Accumulation of +ve charge from H2CO3 dissocation that produces H+ taken away from negatively charged amino acids within Hb (H+ binds to negative R groups)

Question 25

Where does CO2 bind on Hb?
Where does O2 bind on Hb?
How much of each can bind to Hb?

Answer 25

Globin end of amine chains
Haem part
4CO2+ 4O2 can bind to 1 Hb

Question 26

CO2 transport
Methods?
What transports most of CO2?
Change in dissolved CO2 compared to O2

Answer 26

CO2 as HCO3-
HbCO2
C(D)CO2
Added alltogether= total CO2 (CO2 flux can be calculated from artery to vein then x by CO like O2)
Bicarbonate
Change= less significant because doesn’t have sigmoid curve like O2

Question 27

CO2 dissociation curve shape
Draw it
(slide 31, lecture 4)
Label artery+ vein positions
Downwrads shift effect?

Answer 27

Linear
Haldene effect= when Hb have bound O2 in all binding sites, won’t bind to CO2 (working in opposite directions) (therefore at higher O2 concentrations, downwards shift)

Question 28

Pulmonary transit time
Same as?
CO2 vs O2?

Answer 28

Amount of time blood is in contact with respiratory exchange surface
Amount of time it takes for O2 to equilibriate
CO2 does it quicker than O2

Question 29

Ventilation-perfusion matching
As you go down the lung?
Difference in impact on ventilation vs perfusion?
Change in perfusion+ ventilation+ ventilation/perfusion ratio on a graph?
(slide 34, lecture 4)
Ideal point on graph?

Answer 29

P(PL) is less negative= Smaller transmural pressure gradient
Alveoli= smaller+ more compliant
More ventilation

Higher intravascular pressure (gravity effect)
More recruitment
Less resistance
Higher flow rate
More perfusion

Greater impact on perfusion in different zones compared to ventilation because blood flow is denser+ more susceptible to changes in gravity

Where they all intercept= ideal lung environment