Week 4 RM - Gas Diffusion

Question 0

How does Boyle’s law relate to the mechanism of breathing?

Answer 0

Air in inspired due to an increase in volume of the thoracic cavity, and as such a corresponding decrease of pressure. It drops below atmospheric pressure and air flows into the lungs

Question 1

What is Boyle’s law?

Answer 1

Pressure is the inverse of volume

Question 2

What is Henry’s law?

Answer 2

The amount of gas dissolved in solution is proportional to the partial pressure exerted by the gas above it

Question 3

What is Fick’s law all about?

Answer 3

The efficiency of gas dissuasion across the respiratory membrane

Question 4

What factors effect gas diffusion across the respiratory membrane?

Answer 4

The diffusion constant (to do with the solubility of the gas)
Difference in partial pressures of the gas
Surface area of the diffusion membrane
Thickness of the membrane

Question 5

What is methemoglobin?

Answer 5

Haemoglobin where the iron at the centre of the heme portion is in its ferric (Fe3+) state rather than its ferrous (Fe2+) state. Cannot bind oxygen and the blood looks a bluish brown when excess amounts are present

Question 6

How is methemoglobin converted back to normal haemoglobin?

Answer 6

The enzyme methemoglobin converts it back to Fe2+ and is dependent on NADH

Question 7

What is Hb saturation?

Answer 7

The percentage of haeme units which contain oxygen molecules. Usually around 97% exiting the lungs

Question 8

How does haemoglobin increase the oxygen carrying capacity of the blood?

Answer 8

If not present, only dissolved O2 would circulate. Haemoglobin grabs oxygen from the plasma, and does not contribute to the partial pressure present in the blood. This allows more O2 to dissolve and continually load onto the haemoglobin, greatly increasing how much oxygen can circulate to the tissues

Question 9

What is co-operativity?

Answer 9

The more oxygen bound to haemoglobin, the easier it is to bind more. Higher concentrations of oxygen will encourage the relaxed state, and favour loading of oxygen onto the haemoglobin molecule.

Question 10

What is the partial pressure of oxygen and carbon dioxide in the alveoli?

Answer 10

100mmMg for O2 and 40mmMg for CO2

Question 11

What is the partial pressure of oxygen in an RBC that has circulated and come back to the alveoli, ready to pick up more oxygen?

Answer 11

40mmMg

Question 12

How does this difference in partial pressure facilitate gas exchange?

Answer 12

The plasma and RBCs have a lower partial pressure of O2 than that of the alveoli, and so oxygen will move down its pressure gradient into the plasma and into the RBC.
PCO2 is greater in the RBC than the alveoli, so CO2 will move out of RBC, into plasma and back into alveoli

Question 13

What is haemoglobin’s buffering Capacity?

Answer 13

Even when pCO2 is the alveoli decreases, oxygen saturation of the haemoglobin remains high - still above 90% even when pO2 is 70mmMg

Question 14

How is oxygen unloaded to the tissues?

Answer 14

The pO2 in peripheral capillaries is roughly around 40mmMg when at rest, and so RBCs traveling there with a higher pO2 will unload down pressure gradient

Question 15

What conditions will shift oxygen dissociation curve to the right?

Answer 15

Increased pCO2
Acidity
Increased temperature
2,3DPG

Question 16

How is haemoglobin prevented from picking up the oxygen it just unloaded at the tissue?

Answer 16

Increased CO2 leads to increased H+ ions which bind to the haemoglobin and stabilise it in the T state. This prevents oxygen from binding and favours the unloading of oxygen - Bohr effect

Question 17

What is the root effect?

Answer 17

Essentially just a part of the Bohr effect, in that the O2 carrying capacity of Hb is decreased due to acidity

Question 18

What effect will shifting the oxygen dissociation curve to the left have?

Answer 18

Will increase oxygen loading in the alveoli

Question 19

What are the different ways in which carbon dioxide is transported in the body?

Answer 19

5-10% in plasma dissolved
23-30% bound to Hb
60-70% as bicarbonate ions in plasma

Question 20

How does the bicarbonate buffer system work in transporting carbon dioxide back to the alveoli?

Answer 20

pCO2 plasma is less than that within tissues, so CO2 exits cells and dissolves into plasma. CO2 enter des RBC and converted to H2CO3 via carbonic anhydrase. H+ dissociates and HCO3- ion is formed. It exits the RBC and travels in the plasma. (Cl- ion replaces to balance charge) The H+’binds to Hb and stabilise it in T state. When at alveoli, high O2 causes H+ to dissociate from the Hb and exits into plasma, forming CO2 and then diffusing into alveoli.

Question 21

Why does more carbon dioxide travel dissolved in the plasma than oxygen?

Answer 21

It is more soluble than oxygen in water

Question 22

Why does alveolar air have different partial a pressures than atmospheric air?

Answer 22

It is only partially replaced by atmospheric air each breath
O2 is constantly being absorbed into pulmonary blood
CO2 is constantly being absorbed from the pulmonary blood back into the alveoli

Question 23

How quickly is gas removed from alveoli and why is this useful?

Answer 23

Half the lungs volume is removed/exchanged every 17 seconds. This slow turnover is important as it prevents sudden changes in gas concentration from a single breath