B3L4 Oxygen Diffusion & Partial Pressure

Dalton’s law

Law stating that each gas in a mixture exerts a pressure proportional to its concentration in the mixture

O2 → 21% of atmospheric pressure

Describe the oxygen cascade by describing structures along with their associated partial pressure of oxygen

1. Trachea (150 mmHg)

2. Alveoli (100 mmHg)

3. Pulmonary veins (95 mmHg)

4. Arterial (90 mmHg)

5. Tissues (40 mmHg)

Why does the partial pressure of O2 drop in the trachea?

Drops because the inhaled air is humidified (add water vapor)

PO2,trachea = (750mmHg - 49mmHg) * 21% = ~150 mmHg

• Subtracting partial pressure of water vapor from atmospheric pressure

(~150 mmHg)

Why does the partial pressure of O2 drop in the alveoli?

Partial pressure decreases because the incoming air is mixing with a lower O2 concentration

(~100 mmHg)

Why does the partial pressure of O2 drop in the pulmonary veins?

Due to diffusion inequality

• Some alveoli are underperfused with O2 and therefore less oxygen diffuses to the pulmonary veins

(~95 mmHg)

Why does the partial pressure of O2 drop in the arteries?

Drops due to shunting: oxygen has been removed from the blood due to vessel use in the conduction zone/Thebesian vessels (used to deliver O2 to the heart)

~90mmHg

Why does the partial pressure of O2 drop in the tissues?

Because O2 is being used for cellular respiration

~40mmHg

Transit Time

The amount of time it takes for blood to pass through the pulmonary capillaries (how long it stays in the pulmonary circuit) with respect to cardiac output

TT = PBV/Q

• Q = cardiac output (L/min)

• PBV = pulmonary blood volume (L)

Exercise-Induced Arterial Hypoxemia

Condition in which blood is passing so quickly (reduced transit time) in the pulmonary capillaries that the BLOOD does not have time to equilibrate with atmos/alveolar PO2

• Less oxygen in the blood

• Occurs exclusively in highly endurance-trained female athletes