Gas exchange and transport

Question 1

what is convection?

Answer 1

the movement of currents within fluids

Question 2

what is diffusion?

Answer 2

the process by which molecules intermingle as a result of their kinetic energy of random motion.
very quick and only occurs over very small distances

Question 3

what is fick’s law of diffusion?

Answer 3

the rate of transfer of a gas through a sheet of tissue is proportional to
tissue area
difference in gas partial pressure between two sides
diffusion constant
inversely proportional to tissue thickness

Question 4

what is fick’s law of diffusion in terms of respiratory physiology?

Answer 4

concentration / pressure gradient
gas solubility
thickness of alveolar membrane
surface area of alveolar
ventilation / perfusion matching

Question 5

what is partial pressure?

Answer 5

the amount of gas dissolved in the plasma

Question 6

which has a larger pressure gradient, O2 or CO2 and why?

Answer 6

O2 has a larger pressure gradient because CO2 is 20x more soluble

Question 7

how long does full O2 loading take?

Answer 7

0.25 seconds

Question 8

when diffusion is impaired, is O2 or CO2 more affected?

Answer 8

O2 is more affected as it is less soluble

Question 9

how thick is the alveolar membrane and how does this affect gas exchange?

Answer 9

0.5-1um thick, very thin to facilitate gas exchange via diffusion rapidly and efficiently

Question 10

what can cause alveolar membrane thickening?

Answer 10

inflammation
infection
fibrosis

Question 11

what can cause temporarily loss of alveoli surface area?

Answer 11

bronchial obstruction (tumour, mucus plug)
atelectasis (lung collapse)
consolidation (alveoli filled with inflammatory fluid)

Question 12

what can cause permanent loss of alveoli surface area?

Answer 12

emphysematous bullae

Question 13

which part of the lungs is best ventilated?

Answer 13

lower part

Question 14

which part of the lungs is best perfused?

Answer 14

lower part

Question 15

what are the 2 autoregulatory homeostatic mechanisms that are triggered to compensate for shunt?

Answer 15

hypoxic pulmonary vasoconstriction (HPV) or dilation
bronchiole response (constriction or dilation)

Question 16

what happens to the pulmonary arterioles during high ventilation (e.g. during exercise)?

Answer 16

the arterioles dilate to optimise V/Q matching and maximise gas exchange

Question 17

what happens in a V/Q scan?

Answer 17

patient breathes in a radio-labelled isotope which can be seen on the scan
the same radio labelled isotope is injected so the pulmonary circulation can be seen on the scan
scan can diagnose if patient has a shunt, with or without compensatory HPVC or alveolar dead space

Question 18

what are the two ways oxygen is transported in the blood?

Answer 18

in solution (dissolved in plasma)
combined with haemoglobin

Question 19

how much oxygen is transported in plasma?

Answer 19

2% - it is a inefficient means of transport because O2 is poorly soluble in water

Question 20

how much oxygen is transported combined with haemoglobin?

Answer 20

98%

Question 21

what is the compound called when oxygen combines with haemoglobin?

Answer 21

oxyhaemoglobin (HbO2)

Question 22

how many O2 binding sites does a Hb molecule have?

Answer 22

4

Question 23

in combination with Hb, how much O2 can blood routinely transport per 100ml of blood?

Answer 23

20ml

Question 24

how long does it take or a O2 molecule to bind to a Hb molecule?

Answer 24

<0.01 seconds and triggers even more rapid binding of the 2nd, 3rd and 4th O2 molecule

Question 25

what is the equation for O2 binding with Hb?

Answer 25

HHb + O2 <-> HbO2 + H+

Question 26

what is the O2 dissociation curve?

Answer 26

the sigmoid shaped curve that shows how readily O2 binds or dissociates from Hb

Question 27

how does O2 get from the blood to the tissues?

Answer 27

it dissociates from Hb and dissolves in the plasma, and then diffuses into the tissue cells

Question 28

what is SaO2?

Answer 28

The percentage of Hb in the blood that is bound to O2

Question 29

what factors affect O2 dissociation?

Answer 29

primarily concentration of O2 increased CO2 at tissue increased temperature reduced pH increased DPG (increased metabolism, occur during exercise, shift curve to the right)

Question 30

what happens to the O2 dissociation curve during exercise?

Answer 30

shifts down and to the right - dissociation happens more quickly to facilitate more O2 supply to the tissues and more CO2 removal

Question 31

what is DPG?

Answer 31

a product of RBC glycolysis and metabolism

Question 32

what increases DPG?

Answer 32

exercise fever acute altitude acute hypoxia chronic hypoxia

Question 33

how much CO2 is transported in solution?

Answer 33

10%

Question 34

how much CO2 binds to the globin portion of the Hb?

Answer 34

20%

Question 35

how much Co2 is transported as bicarbonate?

Answer 35

70%

Question 36

what are the three ways CO2 is transported?

Answer 36

in solution binded to Hb as bicarbonate

Question 37

what are the two ways CO2 is converted to HCO3- (bicarbonate)

Answer 37

in the plasma (slow) on the RBC where a catalyst called carbonic anhydrase speeds up the reaction by 1000 times

Question 38

what is the equation for CO2 -> HCO3-?

Answer 38

CO2 + H2O <-> H2CO3- <-> HCO3- + H+

Question 39

why is exhaled breath moist?

Answer 39

because it has a water content