PHYS Transport of Gases & Control of Breathing - Week 1

Question 1

2 x ways O2 is transported (state the main way):

Answer 1

1. Dissolved in plasma & erythrocyte cytoplasm (very low concentrations of O2 travel via this mechanism)
2. Reversibly bound to Hb

Question 2

PO2 of tissues. PO2 lungs. PO2 60mmHg = …& O2 sat.

Answer 2

40mmHg. 100mmHg. 90%.

Question 3

4 factors which cause right O2/Hb dissociation curve shift

Answer 3

Acidosis, increased PCO2, increased temp, increased 2,3-DPG.

Question 4

What does right shift trigger Hb to do?

Answer 4

Offload O2, so that CO2 uptake can be increased & waste products cleared from the body.

Question 5

How long does it take for equilibrium btw alveolus & pulmonary capillary to be reached for PO2?

Answer 5

0.25s. PO2 shoots from 40mmHg -> 104mmHg. Remember: 4.

Question 6

3 x ways CO2 is transported (state the main way):

Answer 6

1. Dissolved in plasma (very low concentrations of CO2 travel via this mechanism)
2. Chemically bound to Hb (HbCO2 )
3. As bicarbonate ions in the plasma (HCO3-) (high concentrations of CO2 travel via this mechanism)

Question 7

Solubility of CO2 vs O2

Answer 7

CO2 20x more soluble (diffuses easier across alveoli membrane).

Question 8

2 x ways breathing is controlled:

Answer 8

• Neural pathways – automatic rhythm & modulation
• Chemical control by O2 & CO2 and chemoreceptors – modulation of rhythm

Question 9

Ventral Respiratory Group (VRG) function

Answer 9

Stimulates expiratory motor neurons.

Question 10

Dorsal Respiratory Group (DRG) function

Answer 10

Stimulates inspiratory motor neurons.

Question 11

Effect of pneumotaxic centre on breathing

Answer 11

Inhibits I
Remember: Tax on breathing.

Question 12

Effect of apneustic centre on breathing

Answer 12

Stimulates I

Question 13

Central chemical control of ventilation originates from chemoreceptors located…?

Answer 13

Medulla

Question 14

Medullar chemoreceptors respond to what to control breathing

Answer 14

Increase in PCO2 indirectly by measuring [H+]/pH in the ECF.

Question 15

Peripheral chemical control of ventilation originates from chemoreceptors located…?

Answer 15

Carotid & aortic bodies.

Question 16

Peripheral chemoreceptors respond to what to control breathing

Answer 16

Direct PO2/PCO2 conc. (alongside central chemoreceptors)
& changes to [H+] (solely).

Question 17

O2 blackout zone begins at what PO2

Answer 17

40mmHg

Question 18

Dangers of dive with hypocapnia.

Answer 18

Hypocapnia = low O2. This is triggered by hyperventilation pre-dive (either consciously or due to exertion). As a result, trigger to breath is not reached until individual has entered O2 blackout zone -> hypoxia -> loss of consciousness -> body reacts and forces a breath -> drowning death (without immediate rescue).