O2 & CO2 Transfer Between Alveolus, Blood & Tissue

Question 1

what does gas movement through conducting airways occur by

Answer 1

convection

Question 2

how does gas exchange across the blood gas barrier in alveolus occur by

Answer 2

diffusion

Question 3

what two ways is oxygen transported in the blood

Answer 3

physical - plasma soluble O2 (2%)
* Less Soluble than CO2
* Function of Partial Pressure of O2 in alveolus
* 0.3ml O2/100ml blood at PO2 of 100mmHg
(= normoxic alveolar PO2 )

chemical - O2 bound to Hemoglobin (98%)
* Rapid and reversible interaction
* Reversibility enables O2 off-loading to tissues
* Hb + O2 ↔ HbO2
Physical

Question 4

how much oxygen is carried by haemoglobin

Answer 4

1.34 x 15 = 20mls O2/ 100ml

Question 5

what is the difference between oxygen content and saturation

Answer 5

Determined by amount of Hb and O2 in blood

Proportion (%) all haemoglobin present how much oxygen is bound to that haemoglobin

Question 6

Saturation can remain the same even if O2 content of blood differs

Question 7

capacity is concentration

Question 8

describe the oxyhemoglobin dissociation curve

Question 9

what factors alter the Hb-o2 affinity shift position of oxyheamoglobin dissociation curve

Answer 9

• Normal P50 = 27mmHg at pH 7.4 and PCO2 of 40mmHg
• Left Shift P50 = increased Hb-O2 affinity and reduced O2 offloading to tissues (eg Fetal Hb)
• Right Shift P50 = decreased Hb-O2 affinity and raised O2 offloading to tissues (eg High Altitude)
• Right Shift P50 may be induced by stressors such as acidosis, fever and hypoxia

Question 10

describe how in the bohr effect, CO2 releases O2 from Hb

Answer 10

1. Production of Carbonic Acid in Red Cell
   CO2 + H2O → H2 CO3 ↔ HCO3- + H+
2. 2. Carbamate Reaction at N-terminal
      Amino Groups on Hb a-subunit
      CO2 + R-NH2 ↔ R-NH-COO- + H+

both cause acidification and lower affinity for oxygen

Question 11

describe the bohr effect

Answer 11

1. CO2 dissolves into plasma & red cell
   along partial pressure gradient
2. Low tissue O2 favours CO2 carriage by blood (HALDANE EFFECT)
3. Carbamate reaction reduces HbO2 affinity (BOHR EFFECT)
4. Carbonic Anhydrase reaction generates carbonic acid which
   protonates. HCO3- leaves cell and maintains inward CO2 gradient
5. Increased red cell [H+] reduces HbO2 affinity by promoting ab Hb subunit interaction (BOHR EFFECT).

Question 12

describe the haldane effect

Answer 12

1. O2 dissolves into plasma & red cell
   along partial pressure gradient
2. High affinity of Hb for O2 reverses
   Hb carbamation and protonation raising
   availabiity of high affinity Hb (BOHR EFFECT).
3. CO2 diffuses into alveolus along
   pressure gradient. High PO2 decreases
   CO2 affinity for Hb (HALDANE EFFECT)
4. Movement of CO2 out of red cell increases HCO3- uptake (Cl- moves out)
5. Proton release from Hb and ↑[HCO3-] drive carbonic anhydrase reaction in reverse,
   maintaining outward CO2 gradient and lowering plasma bicarbonate

Question 13

how does Redirecting Blood & Gas Flow Away from Poorly Ventilated/Perfused
Lung Regions

Answer 13

• poor ventilation and large blood flow – need to reduce perfusion - hypoxia constricts pulmonary
  arterioles to increase
  pulmonary transit time of blood (Q). Re-directs blood
  flow to well- ventilated areas of lung
• good ventilation and poor blood flow – need to reduce ventilation - low CO2 constricts bronchioles
  Re-directs air flow in lungs away from obstruction