Gaseous diffusion and transport

Question 1

How much is 1kPa in mmHg

Answer 1

7.5mmHg

Question 2

PB equation

Answer 2

PB=PO2+PCO2+PN2+PH2O

Question 3

PO2 equation

Answer 3

PO2=FO2xPB

Question 4

PB at sea level

Answer 4

around 101kPa

Question 5

What happens to PO2 as altitude increases

Answer 5

falls

Question 6

What is Henry’s law and what does it show

Answer 6

Concentration=kxPressure

Higher partial pressure of gas above liquid=more dissolves

Question 7

What is Henry’s law constant (k) determined by

Answer 7

Solubility

Question 8

Why do divers get the bends when they ascend too quickly

Answer 8

Henry’s law. bubbles in blood because less N2 gas dissolved as pressure decreases which causes pain

Question 9

What is PH2O determined by and what is the value in human alveoli?

Answer 9

Determined by temperature and saturation. Always 6.3kPa in humans because body temp constant and 100 saturation by the time air reaches lungs

Question 10

PIO2 equation

Answer 10

PIO2=(PB-PH2O)xFO2=(PB-6.3)x0.209

Question 11

Why PAO2 not measured directly

Answer 11

More O2 is used than CO2 produced. So instead of PAO2=PIO2-PACO2,, PAO2=PIO2-PACO2/R where R=CO2 production/O2 consumption. R is normally around 0.8. This is the alveolar gas equation

Question 12

Make a table of numbers for: PO2, PCO2, PH2O x atmospheric air, mixed expired, trachea, alveolar gas

Answer 12

Ref. notes

Question 13

What are the figures for PVO2, PAO2 and PCO2

Answer 13

PVO2=5.3kPa, blood entering capillaries from pulmonary artery
PAO2=13.5kPa
PCO2=13.5kPa, once O2 diffuses in with the gradient, matches alveolar

Question 14

Why does CO2 equilibriate rapidly through alveolar-capillary exchange surface?

Answer 14

Although it diffuses at 85% rate of O2, higher solubility coefficient which makes it 23 times more soluble. For any given partial pressure, it diffuses 23x0.85=20 times faster than O2

Question 15

Draw graphs for time in capillary against PO2 and PCO2 for normal and abnormal

Answer 15

ref. notes

Question 16

Rate of transfer of gas through a sheet of tissue is proportional to

Answer 16

Area/Thickness(PA-PC)

Question 17

DLg

Answer 17

gas transfer factor or gas diffusing capacity. A/T

Question 18

Rate of transfer of gas equation

Answer 18

Rate of transfer of gas=DLg(PA-PC)

Question 19

Oxygen diffusing capacity and carbon monoxide diffusing capacity

Answer 19

O2: DLO2=oxygen uptake from lungs/(PAO2-PCO2) NB PCO2 unmeasurable
CO: DLCO=CO uptake from lung/PACO because CO high affinity. DLCO=TLCO

Question 20

What happens to rate of transfer of gas equation in emphysema and fibrosis

Answer 20

Emphysema: A reduced so Vgas reduced
Fibrosis: T increases so Vgas reduced

Question 21

How to increase and decrease DLCO

Answer 21

Increase: increase in pulmonary blood volume, polycythaemia (elevated haematocrit)
Decrease: reduction in alveolar-capillary membrane area, increased thickness of alveolar capillary membrane

Question 22

Use the solubility of O2 in blood and normal arterial PO2 to work out how many ml of O2 dissolved in each ml of blood. Work out cardiac output needed if resting O2 consumption is 250mlmin^-1

Answer 22

Solubility of O2=0.000225ml^-1kPa^-1
Arterial pO2=13kPa
13x0.000225=0.003ml
Resting O2 consumption=250mlmin^-1
Cardiac output=250/0.003=83000mlmin^-1

Question 23

HbA structure

Answer 23

2 identical alpha and beta chains. Haem group is iron-porphyrin compound. Iron in ferrous form and binds and O2 molecule

Question 24

Capacity, content, saturation define in relation to RBC

Answer 24

capacity=Hb conc in bloodxhow many ml O2 each gram of Hb can bind with (200ml/l)
oxygen content=nearly all binding sites filled at pulmonary capillaries so (200ml/l)
saturation: % of sites filled. (100% at pulmonary capillaries and 75% for mixed venous blood)

Question 25

Draw Hb dissociation curves with 2 lines and O2 content+saturation on y axis. Note down what causes shift to right and left

Answer 25

y axis O2 content up to 200ml/l. Shift to left caused by: decrease in pCO2, increase in pH, decrease in temperature, decrease in 2,3 DPG

Question 26

For Hb dissociation curve note down normal arterial blood and resting mixed venous values for:PO2, O2 content and O2 saturation

Answer 26

Arterial: PO2=13.3kPa, O2 content=200ml/l, O2 saturation=97%
Venous: PO2=5.3kPa, O2 content=130ml/l, saturation=75%

Question 27

What happens to oxygen capacity, content and saturation at high altitude

Answer 27

Capcity=same, content=reduced, saturation=reduced

Question 28

Hb dissociation curve which kPa dangerous and why

Answer 28

around 8 because small change in pKa changes greatest degree of affinity

Question 29

What happens to oxygen capacity, content and saturation for anaemia

Answer 29

Capcity=reduced, content=reduced, saturation=normal