Blood Gas Transport - Lecture 19

Question 1

What is gas exchange dependent on?

Answer 1

○ Diffusion surface area
○ Diffusion distance for gases
○ Concentration gradient between alveolar air and blood
○ Solubility of gases
○ Coordinated blood flow and airflow

Question 2

What is the composition of gases in the atmosphere?

Answer 2

○ N2 = 78.6% = 597mmHg
○ O2 = 20.9% = 159mmHg
○ CO2 = 0.04% = 0.3mmHg
○ H2O = 0.46% = 3.7mmHg

Question 3

What is the composition of gases in the alveoli?

Answer 3

○ N2 = 75.4% = 573mmHg
○ O2 = 13.2% = 100mmHg
○ CO2 = 5.2% = 40mmHg
○ H2O = 6.2% = 47mmHg

Question 4

What is Dalton’s law?

Answer 4

The total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture

Question 5

What is the movement of gases in the pulmonary circuit?

Answer 5

○ Oxygen moves from the alveolus to the capillaries
○ Carbon dioxide moves from the capillaries into the alveolus

Question 6

What is the movement of gases in the systemic circuit?

Answer 6

○ Oxygen moves from capillaries to systemic tissue
○ Carbon dioxide moves from systemic tissue to capillaries

Question 7

What does haemoglobin do?

Answer 7

○ Each Hb molecules binds to 4 molecules of oxygen
○ After binding to O2, Hb changes shape to facilitate further uptake (positive feedback)
○ Rapid and reversible

Question 8

How is oxygen transported in the blood?

Answer 8

○ 97% of O2 transported in blood in combination with Hb
○ Remainder in plasma

Question 9

What is Hb saturation?

Answer 9

The percentage of haem units in a Hb molecule that contain bound oxygen e.g. 4 molecules bound to Hb = 100% saturated

Question 10

What can affect oxygen binding to Hb?

Answer 10

○ Parital pressure of oxygen in blood
○ Blood pH
○ Temperature
○ State of O2 binding of the Hb molecule

Question 11

What does the oxygen-Hb dissociation curve show?

Answer 11

The higher the partial pressure of oxygen, the more oxygen combines with Hb

Question 12

How does pH and CO2 affect the dissociation curve?

Answer 12

○ Decrease in pH & Increase in CO2:
- Curve shifts to the right
- Decreased affinity for O2 so gives it up easier
- Happens when exercising
○ Increase in pH & Decrease in CO2:
- Increased affinity of O2
- Keeps hold of O2

Question 13

How does temperature affect the dissociation curve?

Answer 13

Increasing temperature: shifts curve to the right so decreased affinity for oxygen

Question 14

What is carboxyhaemoglobin?

Answer 14

○ CO binds tighter than O2
○ Dramatically reduces ability of O2 to bind to Hb

Question 15

What is methaemoglobin?

Answer 15

○ Fe2+ oxidised to Fe3+ by drugs
○ Unable to carry O2
○ Slowly converted back

Question 16

What is fetal haemoglobin?

Answer 16

○ 2 alpha + 2 gamma subunits
○ Higher affinity for O2
○ Important for transferring O2 across the placenta

Question 17

How is CO2 transported in the blood?

Answer 17

○ 70% converted to carbonic acid formation and transported in plasma as bicarbonate ion
○ 23% bound to haemoglobin (carbaminohaemoglobin)
○ 7% Dissolved in plasma

Question 18

How is carbon dioxide converted to carbonic acid?

Answer 18

○ Reacting with water and using an enzyme known as carbonic anhydrase
○ Carbonic acid decomposes into H+ and bicarbonate ion

Question 19

What is chloride shift?

Answer 19

Maintains electrical stability of RBCs

Question 20

How does carbon dioxide bind to haemoglobin?

Answer 20

Binds to ammonia group to form carbamino group

Question 21

How is H+ managed?

Answer 21

○ Imidazole groups of histidine residues in haemoglobin
○ Deoxygenated haemoglobin has the strongest affinity for H+

Question 22

What is the haldane effect in the lungs?

Answer 22

Oxygenation of Hb -> Lower affinity for H+ ions -> decreased buffering power -> Release of H+

Question 23

What is the haldane effect in the tissues?

Answer 23

Deoxygenation of Hb -> Higher affinity for H+ ions -> increased buffering power -> H+ uptake