Transport of O2 and CO2 in blood and tissue

Question 1

How does the pulmonary capillary blood remain the same PO2 saturation during exercise?

Answer 1

Even though the time spent in the lungs is decreased by half due to increased cardiac output, there is still the same amount of PO2 because:
1. increased surface area + improved ventilation/perfusion match = increased diffusing capacity
2. transit time safety factor: the majority of the gas exchange occurs in the first 1/3 of the pulmonary capillary bed, so still have the same O2 saturation despite increased cardiac output

Question 2

How come the atrial PO2 is only 95 mm Hg?

Answer 2

• due to bronchial venous shunting
• about 2% of the blood that enters the L atrium did not go through the pulmonary capillaries –> PO2 = 40mm Hg
• therefore diluting the PO2 from 104 to 95

Question 3

What are the 2 factors that can affect tissue PO2 diffusion rate?

Answer 3

1. rate of blood flow and tissue O2 delivery: increased blood flow improves O2 delivery due to increased quantity of O2 during a given time
2. rate of tissue metabolism: increased tissue metabolism decreased PO2 in the interstitial fluid

Question 4

What does the sigmoid shape of the oxygen-hemoglobin dissociation curve mean?

Answer 4

• hemoglobin’s affinity for O2 increases as O2 is bound to it
• highest affinity @ 95 mm Hg
• lowest affinity @ 40 mm Hg

Question 5

How does an increase in O2 demand, temperature, H+ shift the oxygen-hemoglobin saturation curve?

Answer 5

shifts to the right

Question 6

Other than transport of O2, what is another important function of hemoglobin?

Answer 6

Tissue O2 buffer!
- makes sure the PO2 remain relatively constant