L37: Gas Exchange

Question 1

What is diffusion limited gas exchange?

Answer 1

The total amount of gas transported across the alveolar/capillary barrier is limited by diffusion and as long as partial pressure gradients for gasses are maintained, diffusion across capillary will continue.

Question 2

Is CO diffusion or perfusion limited?

Answer 2

Diffusion limited

Question 3

Does CO equilibrate in the capillary? What happens to the partial pressure of CO?

Answer 3

No equilibration.

The partial pressure gradient is maintained along the length of the capillary which facilitates continued to diffusion. The PaCO does not increase too much because CO binds to Hemoglobin and it needs to be free CO to contribute to partial pressure

Question 4

What is perfusion limited gas exchange?

Answer 4

The total amount of gas transported across the alveolar/capillary barrier is limited by blood flow through the capillaries.

Question 5

If the partial pressure gradient is not maintained, what is the only way to increase gas transport in perfusion limited exchange?

Answer 5

Increase blood flow.

Question 6

Is O2 normally perfusion or diffusion limited? How can this change?

Answer 6

Normally perfusion limited.

It can become diffusion limited if there is insufficient time for equilibration to occur between the blood, the diffusion capacity is low, or the PAO2 is abnormally low (High altitude)

Question 7

Does O2 equilibration occur? What does this mean?

Answer 7

Yes, about 1/3 along the length of the capillary. O2 diffusion will stop here unless blood flow is increased.

Question 8

How does Fibrosis affect O2 diffusion?

Answer 8

The alveolar wall thickens, so increased diffusion distance and decreased diffusion capacity (DL). Rate of diffusion is decreased and partial pressure gradient is maintained along capillary (equilibrium is not reached)

Question 9

What are the two ways that O2 is transported?

Answer 9

• 2% dissolved in blood

- 98% bound to hemoglobin

Question 10

What is Henrys law and the equation associated with it?

Answer 10

The concentration of dissolved O2 is proportional to the partial pressure of O2.

Cx = Px (solubility)

Cx= concentration of dissolved gas
Px= partial pressure of gas

Question 11

What is the solubility constant?

Answer 11

0.003 ml O2/100ml blood/mmHg

Question 12

What are the components of hemoglobin?

Answer 12

4 heme groups that contain reduced iron (Fe2+, Ferrous)

4 polypeptide chains (2alpha and 2 Beta)

Question 13

What is positive cooperativity?

Answer 13

When one oxygen binds to hemoglobin, it increases hemoglobins affinity for more oxygen. It induces a conformational change to expose the remaining binding sites.

Question 14

What is methemoglobin and how is it treated?

Answer 14

When the iron part of the heme is the Fe3+ (Ferric) state and it does not bind to O2.

Can be treated with methylene blue to keep Fe reduced.

Question 15

What causes methhemoglobin?

Answer 15

Chemicals (nitrates/sulfas) or genetically (Decreased methhemoglobin reductase enzyme in RBC)

Question 16

What is fetal hemoglobin?

Answer 16

HbF instead of HbA ( the adult hemoglobin) and contains 2 alpha and 2 gamma chains. It is replaced over the first year of life to HbA.

-Has a higher affinity for O2 than HbA which is good because it facilitates movement of O2 from mom to fetus

Question 17

What is hemoglobin S?

Answer 17

When the B chain has an alteration in the 6th AA (valine instead of glutamic acid).

• O2 affinity of Hbs is less than for HbA.
• Causes sickle cell disease

Question 18

How do you find the O2 binding capacity?

Answer 18

Multiple the amount of hemoglobin in the blood by how much O2 1 g of hemoglobin binds to.

Question 19

What do you call hemoglobin that is not bound to oxygen?

Answer 19

Deoxyhemoglobin

Question 20

What do you called hemoglobin when bound to O2?

Answer 20

Oxyhemoglobin

Question 21

What is the primary factor in determining Hb saturation?

Answer 21

PO2

Question 22

What does P50 refer to?

Answer 22

The PO2 where 50% of Hb is saturated.

Question 23

What shape is the oxygen-hemoglobin dissociation curve?

Answer 23

Sigmoidal with steep increase in % Hb saturation from PO2 of 0-40. The curve levels off between 60-100 PO2.

Question 24

What does it mean when the O2 hemoglobin dissociation curve shifts to the right?

Answer 24

There has been a decrease in affinity of Hb for O2, reflected as an increased P50. There is increased unloading of O2 in the tissues.

Question 25

What factors can decreased Hbs affinity for O2?

Answer 25

1) increased PCO2, decreased pH, and Increased metabolic activity (Bohr effect due to increased H+)
2) Increased temperature
3) 2,3, DPG decreases affinity and is a RBC glycolysis byproduct (seen in chronic hypoxia and high altitude)

Question 26

What does it mean when the O2 hemoglobin dissociation curve shifts to the left?

Answer 26

There has been an increase in Hbs affinity for O2, reflected as a decreased P50. There is decreased unloading of O2 in the tissues.

Question 27

What factors increased Hbs affinity for O2?

Answer 27

1) Decreased PCO2 and increased pH
2) Decreased temperature
3) Decreased 2,3 DPG- decreased metabolism

Question 28

What are the 3 ways that CO2 is transported?

Answer 28

1) Dissolved 5%
2) Bound to hemoglobin 3%
3) As bicarbonate 90% MOST IMPORTANT

Question 29

Is CO2 more or less soluble than O2?

Answer 29

More soluble by 20x

Question 30

What enzyme is involved in the reaction of CO2 to bicarbonate (HCO3-)?

Answer 30

Carbonic anhydrase

Question 31

What is the transporter that moves bicarbonate out of the RBC and Cl- in?

Answer 31

An anion exchanger call Cl-/HCO3- exchanger or Band 3 protein