Respiratory Gas Exchange

Oxygen is transported in RBCs as…

oxyhemoglobin

Carbon Dioxide is transported in RBCs as…

carbaminohemoglobin

The hemoglobin constant is 1.34 mL, why?

represents the amount of oxygen carried by 1g of Hgb

Henry’s Law is meaning that…

the quantity of a gas that will dissolve in a liquid is proportional to the partial pressure of the gas when temp is constant

At high partial pressure, O2 is …. hemoglobin

readily bound to

At low partial pressure, O2 is… hemoglobin

readily dissociated from hemoglobin

Describe the movement of Oxygen. The partial pressure of O2 in arterial blood is about 100 mmHg while venous blood is 40 mmHg. So…

oxygen will flow from the alveolus across the respiratory membrane and down its partial pressure gradient into pulmonary capillaries. Then diffuse into tissues

At what partial pressure is hemoglobin completely saturated with oxygen?

A PO2 of 70 mmHg

Describe the movement of Carbon Dioxide. The partial pressure of CO2 in venous blood in 45 mmHg and partial pressure of CO2 in alveoli is 40 mmHg. So…

CO2 leave tissues, enter capillaries, and move into alveoli to be exhaled.

What does PO2?

The amount of oxygen dissolved in plasma, measured in mmHg

What does SO2 measure?

The Percentage of Hemoglobin bound to oxygen

Which reflects oxygen that is freely available in blood: PO2 or SO2?

PO2

Which reflects oxygen being transported by hemoglobin: PO2 or SO2?

SO2

Describe the Oxyhemoglobin Dissociation Curve

Curve shows how O2 levels in plasma (PO2) relates to how much hemoglobin is carrying oxygen (SO2)

If affinity for oxygen increases, what does hemoglobin do?

Holds oxygen tighter —→ higher SO2

If affinity for oxygen decreases, what does hemoglobin do?

Releases oxygen more easily —→ lower SO2

The ability of hemoglobin to release oxygen is assessed at the P50 point. This is the point at which…

hemoglobin is 50% saturated

On the oxyhemoglobin disassociation curve, a left shift means….

at same PO2, hemoglobin has a higher SO2 —→ so hemoglobin is holding onto oxygen more tightly

A point on the oxyhemoglobin dissociation curve shows a PO2 of 100 mmHg. Is this lungs or tissues?

Lungs (high PO2 —→ oxygen loading)

A point on the oxyhemoglobin dissociation curve shows a PO2 of 40 mmHg. What is happening to oxygen at this location?

Oxygen is being released to tissues (low PO2 —→ unloading)

What causes a shift to the left?

Oxygen is held on to.

1. dec in H+

2. inc in pH

3. dec in temp

4. dec in 2,3 DPG

5. carboxyhemoglobin

What causes a shift to the right?

Oxygen is easily released

1. dec in pH

2. inc in PCO2

3. inc in temp

4. inc in 2,3 DPG

In the red blood cells, what approximate percentage of CO2 binds to hemoglobin as carbaminohemoglobin.

20-23%

The remaining percentage of CO2 reacts with water to form what?

Carbonic acid which dissociates into bicarbonate ion and a hydrogen ion

Once bicarbonate exits the cell and enters the plasma, what enters the RBC to maintaining the balance of charge within the cell?

A chloride ion (this is Chloride Shift)

What is the Haldane effect?

The unloading of oxygen in tissues promotes loading of carbon dioxide

What enzyme converts CO2 and H20 into carbonic acid (H2CO3)?

Carbonic anhydrase

What does carbonic acid quickly dissociate into?

H+ and HCO3- (bicarbonate)

Where does HCO3- formation primarily occur?

Inside RBCs

In the lungs, what happens to bicarbonate?

It moves into RBCs and converted into CO2

What happens to H+ produced during bicarbonate formation in RBCs?

It is buffered by hemoglobin

In the lungs, what happens to CO2 after it is formed from bicarbonate?

It is exhaled

Hypoxemia

A condition with abnormally low oxygen levels in blood

Remember what is normal PO2?

80-100 mmHg

What is normal SO2?

95-100%

What is mild Hypoxemia?

PO2 of 60-79 mmHg

What is moderate Hypoxemia?

PO2 of 40-59 mmHg

What is severe Hypoxemia?

PO2 <40 mmHg

What formula is used to calculate Total Oxygen Content?

((Hgb (g) x 1.34 (Hg constant) x SaO2)) + (PaO2 × solubility constant) = CaO2

Normal value: 18-20 vol%

What is Hgb constant?

1.34 mL O2

What is solubility constant of oxygen?

0.003 mL/mmHg per dL of blood

Determine arterial oxygen content for:

Hgb= 15 g

SaO2 = 98% (convert to decimal)

PaO2 = 100 mmHg

(15 × 1.34 × 0.98) + (100 × 0.003) = 19.9 or 20%