Pulmonary gas diffusion and Gas transport

Question 1

4 factors of Ficks Law

Answer 1

1. diffusion distance
2. surface area for exchange
3. gas solubility
4. partial pressure difference

Question 2

list factors that affects partial pressure difference

Answer 2

1: alveolar gas composition: closer to atmospheric air: high O2 low CO2
2. blood arriving the lungs: are systemic venous blood: deoxygenated and high in CO2
= pressure gradiant
3. FREE gas molecules and Hb molecues:
- hb is O2 sink and CO2 source,
- PaGas affected

Question 3

how many times is CO2 more soluble than O2

Answer 3

20X, so little difference in partial pressure enough to diffuse

Question 4

what constitute the normal thickness for exchange

Answer 4

type 1 pneumocyte
endothelial cells of capillaries
= alveolo-capillary block

Question 5

what influences the SA for exchange x3

Answer 5

1. ventilation: more ventilated: more inflated: more contacy
2. active capillary bed: more diffusion = more distended = more in contact
3. structural changes of the lung reduces SA for exchange: COPD

Question 6

what is DL and why is carbon monoxide used

Answer 6

DL: volume of gas (Vg) diffused across the alveolar-capillary membrane per mmHg change in pressure (PA-Pcap)

• CO used because: it readily diffuses across membrane, is not flow dependent, high affinity for Hb
  = better measurement of PURE DIFFUSION

Question 7

what affects DL

Answer 7

DL = olume of gas exchanged across the MEMBRANE
1. thickness: capillary thickness (fibrosis) OR alveolar thickness (lung fibrosis) or odema anywhere

2. PERFUSION
3. VENTILATION
4. Hb concentration in blood (anaemia)
   = basically all of the ficks factors

Question 8

describe the o2 dissociation curve and its relationship with bohrs effect

Answer 8

NEVER 100% Hb %saturation: 97%
- rest is freely dissolved

P50= O2 tension at which 50% Hb saturation

Hb affinity for O2 decreases when:
CO2 present, H present, increased temperature and 2,3-DPG present

Question 9

describe the process of CO2 transport

Answer 9

• 5% dissolved freely in blood
• rest enters RBC, where:
  20% binds to Hb: carbaminohaemoglobin
  70% forms H2CO3 (CA catalysed) = H+ and HCO3-
  > H binds to Hb side chain
  > HCO3- cl-shift: to keep the equilibrium to right and expelled into blood

Question 10

integrate Haldanes effect and Bohr effect at the tissue and lungs

Answer 10

metabolic tissue: CO2 production and LOW O2
Bohr: presence of CO2: reduce Hb O2 affinity: oxygen offloading to tissue
Haldanes: low O2 levels: increase DEOXYHB affinity for CO2 = CO2 loading

lungs: high O2
- Haldanes: O2 presence: reduce affinity for CO2 by carbominhohB = offloading CO2 diffuse
- Bohr: LOW CO2 presence: displace Hb-CO2, O2 binding displaces H
= H+HCO3 = CO2