Blood Gas Transport

Question 1

What is the process of gas transport?

Answer 1

Carrying O2 from the alveoli to systemic tissues and CO2 from systemic tissues to alveoli

Question 2

What is diffusion in the context of gas transport?

Answer 2

The movement of gases across a membrane depending on surface area, distance, and concentration gradient

Question 3

What is Dalton’s Law of Partial Pressure?

Answer 3

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

Question 4

What is the atmospheric pressure at sea level?

Answer 4

760 mmHg

Question 5

What is Henry’s Law?

Answer 5

The amount of gas that dissolves in water is determined by its solubility in water and its partial pressure in air

At equilibrium, the amount of dissolved gas in solution is proportional to the partial pressure of that gas

Question 6

What percentage of O2 is transported in blood bound to hemoglobin?

Answer 6

Approximately 97%

Question 7

How many molecules of O2 can each hemoglobin molecule bind?

Answer 7

4 molecules

Question 8

What is the Bohr shift?

Answer 8

The rightward shift of the oxygen-hemoglobin dissociation curve due to decreased pH and increased CO2, facilitating O2 unloading

Question 9

What is the composition of adult hemoglobin?

Answer 9

4 globular protein subunits (2 alpha + 2 beta)

Each subunit has protein (globin) and positive non-protein group (haem which has Fe)

Question 10

What is the main way CO2 is transported in the blood?

Answer 10

70% converted to carbonic acid (H2CO3) and transported as bicarbonate ion (HCO3-)

Question 11

Fill in the blank: The amount of dissolved gas in solution is proportional to the _______.

Answer 11

partial pressure of that gas

Question 12

True or False: CO2 is more soluble in blood than O2.

Answer 12

True

Question 13

What is the Haldane effect?

Answer 13

The phenomenon where deoxygenated hemoglobin has a higher affinity for CO2 and H+ ions, aiding CO2 transport from tissues

Question 14

What role do imidazole groups of histidine residues in hemoglobin play?

Answer 14

They act as buffers in red blood cells

Question 15

What effect does increased temperature have on hemoglobin’s affinity for O2?

Answer 15

Decreased affinity for O2, facilitating unloading in active tissues

Question 16

What happens to hemoglobin’s affinity for H+ ions upon oxygenation?

Answer 16

It decreases, reducing buffering power

Question 17

What is the typical arterial PO2 in mmHg at sea level?

Answer 17

159 mmHg

Question 18

What is the primary function of the respiratory membrane?

Answer 18

Facilitating gas exchange between alveolar air and blood

Question 19

What is the significance of the oxygen-hemoglobin dissociation curve?

Answer 19

It relates the saturation of hemoglobin to the partial pressure of O2

Question 20

How does CO2 affect blood pH?

Answer 20

Increases H+ concentration, lowering pH

Question 21

What happens to the oxygen-hemoglobin dissociation curve when 2,3-DPG levels increase?

Answer 21

Shifts to the right, enhancing O2 unloading

Question 22

What is the concentration of CO2 in the alveoli at sea level in mmHg?

Answer 22

40 mmHg

Question 23

What is gas exchange dependent on?

Answer 23

• diffusion surface area of alveoli (large, moist)
• diffusion distance for gases (short)
• concentration gradient between alveolar air and blood (differences in partial pressure)
• solubility (in blood) of gases (CO2 & O2)
• coordinated blood flow and airflow

Question 24

What is Haemoglobin (Hb) saturation?

Answer 24

The percentage of haem units in a Hb molecule that contain bound oxygen

(4 molecules of O2 bound to Hb = fully (100%) saturated)

Question 25

What affects O2 binding to Hb?

Answer 25

1. PO2 of blood (partial pressure of oxygen)
2. Blood pH
3. Temperature
4. State of O2 binding of the Hb molecule (more O2 bound means easier binding)

Question 26

When does O2 unload in tissues?

Answer 26

High temperature aids unloading = high in active tissues

High CO2 & low pH aids unloading = curve shifts to right as Hb has decreased affinity for oxygen

Question 27

What is carboxyhaemoglobin?

Answer 27

When CO2 binds to Hb
- CO2 binds tighter than O2 (200x greater)
- dramatically reduces ability of O2 to bind to Hb
- can be removed but very slowly

Question 28

What is methaemoglobin?

Answer 28

• Fe2+ is oxidised to Fe3+ (changes configuration) by drugs
• unable to carry O2
• slowly converted back

Question 29

What is fetal haemoglobin?

Answer 29

• 2 alpha, 2y
• higher affinity for O2
• important in transferring O2 across the placenta

Question 30

What is chloride shift?

Answer 30

Caused by bicarbonate ions (HCO3-) during CO2 transport

Allows us to maintain electrical stability of cells

Question 31

How does Hb act as a buffer in red blood cells?

Answer 31

• every CO2 —> HCO3- yields an H+
• pH would become very acidic
• minimise the size of pH changes by consuming or releasing H+
• best buffer in red blood cells = imidazole groups of histidine residues in Hb
• deoxygenated Hb has the strongest affinity for H+

Question 32

What is the haldane effect in the lungs?

Answer 32

• oxygenation of Hb
• Hb undergoes conformational changes
• lower affinity for H+ ions
• decreases buffering power
• release of H+
• aids unloading of CO2 in lungs

Question 33

What is the Haldane effect in the tissues?

Answer 33

• deoxygenation of Hb
• Hb undergoes conformational changes
• higher affinity for H+ ions
• increases buffering power
• H+ uptake
• aids CO2 transport from tissues