Gas Exchange and Transport

Question 1

What are atmospheric gasses measured in?

Answer 1

Partial pressure (mmHg)

Question 2

1 atmosphere in mmHg

Answer 2

760mmHg

Question 3

pO2

Answer 3

160mmHg

Question 4

pCO2

Answer 4

.25mmHg

Question 5

pN2

Answer 5

600mmHg

Question 6

Relationship of membranes of alveoli and endothelial cells of pulmonary capillaries

Answer 6

Membranes are fused

Question 7

Fick’s Law

Answer 7

Describes diffusion across a membrane

Gas Exchange = Diffusion constant x (Surface area/Membrane thickness) x Pressure gradient

Question 8

Why is pO2 in alveoli 60mmHg less than pO2 of atmosphere?

Answer 8

Water vapour in airways exerts pressure. Therefore partial pressure of moist air is 150mmHg

Freshly inspired air mixes with stale dead space air

Question 9

Is oxygen or carbon dioxide more water soluble?

Answer 9

Carbon dioxide

Question 10

Forms in which oxygen is carried in the blood

Answer 10

Bound to haemoglobin 98.5%

Free in blood 1.5%

Question 11

Normal amount of O2 dissolved in blood plasma

Answer 11

3mL/L of blood

Question 12

Normal amount of haemoglobin-bound O2 in blood

Answer 12

199mL/L of blood in males

172mL/L in females

Question 13

Which form of O2 can diffuse into cells?

Answer 13

Only dissolved O2.

Hb O2 can’t diffuse into cells

Question 14

Amount of Hg/L in males Vs females

Answer 14

15g in males vs 13g in females

Question 15

Shape of oxygen-haemoglobin dissociation curve

Answer 15

Roughly sigmoid

Question 16

Percentage saturation of O2 of haemoglobin in a resting cell

Answer 16

40%

Question 17

Effect of oxygen-haemoglobin dissociation curve

Answer 17

Affinity of O2 for haemoglobin isn’t changed much by changes in pO2

Question 18

pO2 of capillaries during exercise

Answer 18

Decrease to about 25mmHg

This results in much lower affinity for O2 for Hg, much O2 dissociates into tissues

Question 19

Bohr effect

Answer 19

Right shift of O2-haemoglobin dissociation curve

Affinity of Hg for O2 decreases as curve shifts to the right

Question 20

States that induce Bohr effect

Answer 20

Decreasing pH
Increasing temperature
Increasing [CO2]
Increasing [2,3 DPG]

Question 21

What is 2,3 DPG?

Answer 21

An intermediate of anaerobic metabolism

Levels increase in RBCs with chromic hypoxia, altitude, anaemia

Question 22

Ways that CO2 is transported in the blood

Answer 22

1) Dissolved
2) Bound to haemoglobin (carbamino haemoglobin)
3) As bicarbonate (HCO3-)

Question 23

Amount of CO2 dissolved in blood

Answer 23

7%

Question 24

Amount of CO2 bound to haemoglobin as carbamino haemoglobin

Answer 24

23%

Question 25

Amount of CO2 in blood as bicarbonate

Answer 25

70%

Question 26

How does CO2 in the blood become bicarbonate?

Answer 26

Carbon dioxide and water react to form carbonic acid (H2CO3) Carbonic acid dissociates into H+ and bicarbonate (HCO3-) Carbonic anhydrase catalyses the reaction between CO2 and water

Question 27

Is the reaction to form carbonic acid favourable?

Answer 27

Yes, because of the high [CO2] in tissue capillaries

Question 28

What stimulates carbamino haemoglobin production?

Answer 28

Presence of H+ and CO2 Because of Bohr Effect - Lower pH and higher [CO2] reduce O2-haemoglobin affinity

Question 29

Haldane effect

Answer 29

Increased Hb affinity for CO2 in low-O2 environment

Question 30

What happens to haemoglobin in the lungs?

Answer 30

Haldane effect is reversed CO2 leaves Hb, O2 binds Hb

Question 31

Do central chemoreceptors detect CO2 directly?

Answer 31

No They detect changes in CSF pH from carbonic acid dissociation

Question 32

When do central chemoreceptors detect pO2?

Answer 32

When pO2 < 60mmHg

Question 33

Are the peripheral chemoreceptors strongly stimulated by high pCO2?

Answer 33

No | Only weakly stimulated

Question 34

When do peripheral chemoreceptors detect pO2?

Answer 34

When pO2 < 60mmHg

Question 35

Is decreased blood pH detected directly by peripheral chemoreceptors?

Answer 35

Yes

Question 36

Effects of hyperventilation

Answer 36

``` Increased pulmonary ventilation Increased alkalosis Increased Palveoli O2, Pblood O2 Decreased respiratory drive Decreased Palveoli CO2, Pblood CO2 ```

Question 37

Effect of huypoventilation

Answer 37

``` Decreased pulmonary ventilation Increased respiratory drive Increased acidosis Increased Palveoli CO2, Pblood CO2 Decreased Palveoli O2, Pblood O2 ```