Gas Exchange

Question 1

Rate of general gas diffusion affected by? (3)

Answer 1

Conc gradient (steeper = better)

SA for diffusion (bigger = better)

Length of diffusion pathway (shorter = better)

Question 2

Ideal gas equation

Answer 2

P = (nRT )+ V

Question 3

Grahams Law

Answer 3

“Rate of diffusion is inversely proportional to square root of its molecular mass at identical pressure + temperature”

Smaller mass of gases = more rapid diffusion

Question 4

Henry’s Law

Answer 4

“Amount of dissolved gas in a liquid is PROPORTIONAL to its partial pressure above liquid”

Question 5

Fick’s Law (6)

Answer 5

Partial pressure difference across diffusion barrier

Solubility of gas

Cross sectional area of fluid

Distance molecules need to diffuse

Molecular weight of gases

Temperature of fluid (NOT IMPORTANT FOR LUNGS: assumed 37 degrees)

Question 6

pO2 in alveoli (vs outside envrionement + capillaries)

Answer 6

Compared to external environment = LOW
(due to continuous diffusion of O2 across alveolar membrane)

Compared to capillary = HIGH
(causes net diffusion into the blood)

Question 7

oxyhaemoglobin?

Answer 7

Transports O2 to respiring tissues via bloodstream

= from binding of haemoglobin + O2

Question 8

pCO2 (alveolar vs capillaries vs outside environment)

Answer 8

In capillaries = much HIGHER than in alveoli
= net diffusion across into alveoli

CO2 can then be exhaled:
Alveoli = HIGHER than external environment

Question 9

Layers of diffusion barrier (5)

Answer 9

1) Alveolar epithelium
2) Tissue fluid
3) Capillary endothelium
4) Plasma
5) RBC’s membranes

Question 10

Factors affecting rate of diffusion at alveoli (4)

Answer 10

Membrane Thickness 
(Thinner = faster)

Membrane surface areas
Larger = faster
Lungs normal have large SA (due to many alveoli)

Pressure Differences across membrane

Diffusion coefficient of gas

Question 11

Ventilation rate? (V)

Answer 11

Vol of gas inhaled + exhaled from lungs in a given time period

=tidal volume (amount of air in / out in one breath) x respiratory rate

Question 12

Perfusion Rate? (Q)

Answer 12

Total volume of blood reaching pulmonary capillaries in a given time period

Question 13

Ventilation vs perfusion (places in the lung)

Answer 13

Ventilation exceeds perfusion towards apex

Perfusion exceeds ventilation towards base

Question 14

Why does gravity trigger differences in V/Q in lung? (2)

Answer 14

Pleural Pressure:
Increased at base of lung
Results in more compliant alveoli + increased pressure

Hydrostatic Pressure
Decreased at apex of lungs
Results in decreased flow + decreased perfusion

Question 15

Management of V/Q mismatch (less ventilation)

Answer 15

Hypoxic vasconsticion = causes blood to be diverted to better ventilated parts of lung

Question 16

Why does oxygen travel on haemoglobin?

Answer 16

Poorly soluble in blood

Question 17

Describe haemoglobin

Answer 17

Protein made up of 4 haem groups (containing Fe2+)

Fe2+ ions associated with hemoglobin molecules = chemically react to form oxyhemoglobin

Haemoglobin molecule = can hold 4 O2 molecules

Question 18

Limiting factor of O2 delivery to tissues

Answer 18

haemoglobin

Question 19

Cooperative Binding

Answer 19

Haemoglobin changes shaped bases on how many O2 molecules bound to it
Shape change = change in O2 affinity

Question 20

T-state of haemoglobin

Answer 20

No oxygen bound = hemoglobin in tense state (T state)

Low oxygen affinity

Question 21

R-state of haemoglobin

Answer 21

At part where 1st oxygen binds hemoglobin alters in shape = relaxed state (R-state)
Higher affinity for oxygen

Question 22

What influences O2 delivery?

Answer 22

% of oxygen bound to hemoglobin = related to pO2 at given site

Question 23

How does cooperative binding work at extreme pO2’s

Answer 23

When LOW pO2 locally : don’t want hemoglobin to keep O2 tightly bound

Where HIGH pO2 locally (e.g pulmonary circulation) : `want haemoglobin to take as much O2 as possible

Question 24

Affect of pH on pO2

Answer 24

Lower pH = more H+

Haemoglobin in T-state it has a higher affinity for H+ than for oxygen

Hemoglobin enters T state + affinity for O2 goes down (more needed to achieve max % saturation)

Bohr Effect = (allows O2 to dissociate with lower pH)

Question 25

Affect of 2-3,biphosphoglycerate on pO2

Answer 25

Product of ANAEROBIC glucose metabolic pathway

Decrease affinity of hemoglobin + oxygen

2-3BPG = increases while at high altitudes

Helps adjust to relatively low atmospheric O2
More O2 released at tissue

Higher [2,3-BPG] = dissociation curve shifts right

Question 26

Affect of temperature on pO2?

Answer 26

Higher temperature of O2 = oxygen has more kinetic energy
= more likely to dissociate

More 02 needed for respiring tissues (tend to generate more heat)

Increase in temperature = curve shifts right

Question 27

CO2 + H20 equation

Answer 27

CO2 + H2O → ← H2CO3 → ← H+ + HCO3-

Question 28

Why can’t all CO2 be dissolved in blood?

Answer 28

Blood pH will become acidic due to excess H+

Question 29

Methods of CO2 transportation (3)

Answer 29

CARBAMINO COMPOUNDS
HCO3-
AS DISSOLVED CO2

Question 30

Carbaminohaemoglobin?

Answer 30

CO2 directly binds to amino acids + amine groups of hemoglobin at high conch

Question 31

Haldane effect?

Answer 31

Where O2 conc = lower (e.g respiring tissues) the CO2 carrying capacity of blood INCREASES

Release of O2 from hemoglobin = promotes binding of CO2

Question 32

Carbamino compounds + stabilising pH

Answer 32

CO2 is unable to leave blood cell to contribute to changes in pH (no acidosis!!)

Question 33

Carbamino compounds + Bohr Effect

Answer 33

Stabilises T-state of hemoglobin

Promoting O2 release from subunits (at most active tissues where CO2 production is highest)

When RBC reaches are of high O2 conc again (e.g lungs) = hemoglobin preferentially binds to O2 again

Stabilises R-state = promotes release of co2 (Haldane effect)

Allows more O2 to be picked up + transported away

Question 34

HCO3- production (+ its uses)

Answer 34

CO2 diffuses into RBCs

Converted to H+ and HCO3- by carbonic anhydrase

HCO3- = transported back via chloride bicarbonate exchange

HCO3- = can act as buffer against H+ in blood plasma

Question 35

Deoxyhaemoglobin (what is it + effect)

Answer 35

H+ created by carbonic anhydrase reaction in RBCs = binds to hemoglobin (deoxyhemoglobin)

RBCs rech lungs : O2 binds hemoglobin promoting R-state

Allows release of H+ ions (become free to react with HCO3- (producing CO2 + H2O) where CO2 is exhaled

Question 36

pC02 at periphery tissues + lower alveoli

Answer 36

PCO2 = high at periphery tissues + lower alveoli (where CO2 is being released)

Allows more CO2 to be dissolved in periphery tissue

Released into gas phase at alveoli where pO2 is lower