Zhu: Diffsusion & Transport of O2 and CO2

Question 1

What are the two locations of diffusion and transport of O2 and CO2?

Answer 1

lungs and peripheral tissue. Peripheral Tissue: O2 is needed in the lungs; also must get rid of CO2. O2 moves from capillaries to cells; CO2 diffuses from the cells to the blood capillaries.

Question 2

What are the main factors that affect diffusion rate (Fick’s Law?)

Answer 2

D = (change in P * Area * Solubility) / (distance * square root of MW) - conversely related: the greater the difference in pressure, the greater the area, or the greater the solubility => increase in Diffusion - inversely related: greater distance or molecular weight => decrease in Diffusion

Question 3

What are the 6 things in the respiratory membrane that must be crossed in diffusion?

Answer 3

1. Alveolar Fluid 2. Alveolar Epithelium 3. Alveolar BM 4. IF 5. Capillary BM 6. Capillary Endothelium

Question 4

What determines the ability of the respiratory membrane to transport a gas into and out of the blood?

Answer 4

Diffusion capacity. This is (in these cases, but not always) conversely related to Diffusion Rate. It can be altered with changes in Area, thickness/distance.

Question 5

How does the diffusion rate and capacity change in interstitial edema/emphysema?

Answer 5

DECREASES. The alveolar wall is lost so AREA is decreased, thus the diffusion is decreased. D = (change in P * Area * Solubility) / (distance * square root of MW)

Question 6

How does the diffusion rate and capacity change in alveolar edema/fibrosis?

Answer 6

DECREASES. Fluid enters alveoli which makes the membrane thicker. Distance is increased, therefore Diffusion is decreased. D = (change in P * Area * Solubility) / (distance * square root of MW)

Question 7

How does the diffusion rate and capacity change in exercise?

Answer 7

INCREASES. Recruitment and distension -> increased AREA -> increased Diffusion D = (change in P * Area * Solubility) / (distance * square root of MW)

Question 8

How does the diffusion rate and capacity change in the removal of one lung?

Answer 8

DECREASES. Decreased area -> decreased diffusion. D = (change in P * Area * Solubility) / (distance * square root of MW)

Question 9

How does the PO2 change in inhaled air?

Answer 9

The air is humidified due to the mucus layer -> evaporation sends H2O into the air. So Partial pressure must also include the subtraction of PH2O, which is 47 mmHg. PO2: (760-47)*21%O2 = 150mmHg PN2: (760-47)*79%N2 = 563mmHg

Question 10

What determines partial pressures of O2 and CO2 in Alveolar Air?

Answer 10

1. Alveolar Ventilation (500-150)*12 = 4200ml
2. Rate of O2 absorption/CO2 excretion At alveolar ventilation of 4200, alveolar PO2 is 104mmHg. (per graph). For PCO2: 40mmHg.

Question 11

**Describe diffusion of O2 in the lung.

Answer 11

(insert pic) Blood in the pulmonary artery carries deoxygenated blood with PO2 at 40mmHg. It flows through the pulmonary capillary where it contacts the alveolus with PO2 at 104mmHg. This higher pressure will cause O2 to flow into the capillary until equilibrium is reached, so the pulmonary vein going to the left atria now carries oxygenated blood at PO2= 104 mmHg. Time: total: .75 seconds. (.25s for gas exchange and the remainder is for deox blood to change to ox blood)

Question 12

**Describe diffusion of O2 in peripheral tissue.

Answer 12

Blood in the systemic artery carries oxygenated blood with PO2 at 95mmHg. It flows through the capillary where it contacts the tissue with PO2 at 40mmHg. This lower pressure will cause O2 to flow out of the capillary until equilibrium is reached, so the vein going to the right atria now carries deoxygenated blood at PO2= 40 mmHg.

Question 13

What happens to the diffusion of O2 during exercise?

Answer 13

CO2 stays in the pulmonary circulation for a shorter amount of time (.25s vs .75s), so there is reduced contact time.

Question 14

What happens to the diffusion of O2 with a thicker blood-gas barrier?

Answer 14

Diffusion decreases because it takes more time for diffusion and deoxygenation of blood. If these patients exercise, it gets even worse. Patient cannot get fully oxygenated.

Question 15

Changes of PO2 in circulation (pic).

Answer 15

(pic)

Question 16

How is O2 transported?

Answer 16

Dissolved (3%) Hemoglobin (97%)

Question 17

What are the three types of hemoglobin?

Answer 17

A (adult), F (fetal: higher O2 affinity), S (sickle cell: lower O2 affinity) Valine replaces one of the glutamic acids in sickle cell.

Question 18

Describe O2 capacity and Hb saturation.

Answer 18

O2 capacity: all seats are taken. The MAX amount of O2 that can be bound to Hgb. Hgb saturation: a percentage of binding sites that have O2 attached to them. = [(O2 Hbg-bound)/(O2 capacity)]*100 - there are 4 heme groups that O2 can bind. P50: the PO2 at 50% Hgb saturation. (half of the seats are taken. 30 is the norm.)

Question 19

What is the O2 capacity of a normal person?

Answer 19

20.1 ml O2/100ml blood (15g Hgb per 100 ml blood *1.34 ml O2/g per each Hgb = 20.1)

Question 20

What is the amount of O2 uploaded via gas exchange when reduced blood is returning from tissues at 75% Hgb saturation? When oxygenated blood is leaving the lungs at 97% Hgb saturation? What is the max amount you can upload in one minute of extra O2 absorbed?

Answer 20

75% * 20.1 = 15 ml O2/100ml of blood

97% * 20.1 = 19.5

Max: 19.5-15 = 5 ml O2/100 ml blood

CO = 5000 ml, so 50 times 100 ml

So MAX = 50*5 = 250 ml O2/min

Question 21

How are partial pressures maintained in exercise?

Answer 21

Alveolar ventilation. In exercise, you need to absorb more and upload more. O2 max: 250 CO2 max: 800

Question 22

***What are factors that shift the O2-Hgb dissociation curve?

(**Test Q: know the relationship between factors and pH values)

Answer 22

Shift to right (O2 affinity is reduced so it can be unloaded)

1. Increased H+
2. Increased CO2
3. Increased temp
4. Increased BPG (an end-product of RBC metabolism; leads to chronic hypoxia -> need to unload O2)

*LEFT SHIFT: Hgb F

RIGHT SHIFT: Hgb S

With exercise, CO2 increases; H+ increase and temp increases. this muscle needs more O2 so we need it to unload. top 3 factors seen in exercise. Top 2 are Bohr effect.

Question 23

Diffusion of CO2 in the lung and peripheral tissues.

Answer 23

Peripheral Tissues:

PCO2 in artery end of capillary is at 40; peripheral tissue is at 45. CO2 diffuses from tissue into blood so the venous end of the capillary is now at 45mmHg. (then systemic vein->RA->RV->pulmonary arteries —->

Lung:

PCO2 in artery end of pulm cap is at 45; alveous is at 40. capillary gives CO2 to alveolus to be blown off so the venous end of the capillary is now at 40.

Question 24

Describe the 3 forms of transport for CO2.

Answer 24

1. Dissolved
2. Hgb (don’t bind with heme but stand in the bus and Bind with N-terminus)

**3. HCO3- (MAJOR FORM)

Question 26

How does the body compensate for electrical neutrality during exercise when the body produces a lot of CO2 adn HCO3-?

Answer 26

CHLORIDE SHIFT:

• HCO3- diffuses out of the RBC (H+ is trapped inside)
• Cl- diffuses into the RBC to maintain neutrality

(CO2 is mostly carried by HCO3-)

Question 27

What is the total CO2 excrection?

Answer 27

4 ml CO2/100 ml blood

CO=5000 ml/min

100/5000=50

4*50 = 200 ml CO2/min

Question 28

Deoxygenation of the blood ___________ its ability to carry CO2. This is known at what?

Answer 28

increases; Haldane effect.

Question 29

Overall diffusion and transport of O2 and CO2 (pic).

Answer 29

Question 30

What is the ventilation-perfusion ratio for an average adult male at rest?

Answer 30

Alveolar ventilation is about 4.2 L/min (350*12)

CO = 5 L/min

Va/Q = 42./5 = 0.8

Question 31

**What are the abnormalities of Va/Q?

Answer 31

- Shunt (<0.8) due to decreased ventilation or increased perfusion.Physiological: lower part of the upright lung (bronchial circulation -> pulmonary vein)

EX: obstruction of air flow: decreased V but same Q so some blood leaves without being ventilated (asthma, emphysema)

- Dead space (>0.8) ventilation > blood flow. Physiological: upper part of the upright lung.

EX: obstruction or loss of blood flow