Gas Exchange

Question 1

Partial Pressure of Gases

Answer 1

Each gas in the mixture of air exerts a portion of the total pressure of gas

Question 2

PO2

Answer 2

Air is 20.93% oxygen

PO2 = 0.2093 * 760 = 159mmHg

Question 3

Inspired air is

Answer 3

100% humidified and warmed

Question 4

Lung partial pressure is calculated as a ___ value

Answer 4

dry values, so you have to subtract the effect of water vapor
PH2O = 47mmHg
Trachea = 760 - 47 * 0.21 = 150mmHg

Question 5

When oxygen moves to a fluid medium (blood) PO2 is defined by…

Answer 5

O2 dissolved in solution

Question 6

Gas Exchange depends on…

Answer 6

Diffusion

Gas diffuses from high to low partial pressures

Question 7

Fick’s Law of Diffusion

Answer 7

A/T * D * (P1-P2)
Primary driving force is the pressure gradient
D - coef of gas is proportional to its solubility in the membrane
CO2 is more soluble in membrane

Question 8

Rate of diffusion of gas is proportional to ____ and inversely related to ____

Answer 8

tissue area (A)
and inversely related to tissue thickness (T)

Question 9

Diffusion path for lung

Answer 9

1. Layer of fluid lining the alveolus containing surfactant
2. Alveolar epithelium
3. Epithelial basement membrane
4. Interstitial space
5. A capillary basement membrane
6. Capillary endothelial membrane

Question 10

Lung Interstitum

Answer 10

Very small under normal conditions

Can become enlarged with inflammatory cells and fluid (edema) and this would interfere with gas exchange

Question 11

Diffusion depends on…
O2
CO2

Answer 11

Pressure gradient
O2 = 100 to 40
CO2 = 40 to 46
CO2 = more soluble in membrane, better diffusion coef.

Question 12

Hemoglobin

Answer 12

Pigment in RBCs gives blood red color

Question 13

Oxygen ____ when binding heme

Answer 13

Ox reversibly binds heme

Consists of porphyrin ring and central iron atom

Question 14

Hemoglobin # of Ox molecules can bind

Answer 14

Hemoglobin cooperatively binds 4 oxygen molecules -
Oxygen of 1st heme inc the affinity for 2nd molecule of O2 - when 1st binds, there is more attraction for second and so on until 4 are bound

Question 15

O2 uptake depends on

Answer 15

1. diffusion characteristics (Ficks Law)

2. Pulmonary capillary blood flow

Question 16

Oxygen diffusion along pulmonary capillary - how long to saturate hemoglobin under norm conditions

Answer 16

Only 1/4 of a sec to saturate hemoglobin under normal conditions

Question 17

Oxygen diffusion along pulmonary capillary - how long to saturate hemoglobin with exercise

Answer 17

Changing time blood cells take to fly across the capillary, generally saturation stays the same
Pathology –> can have problem with saturation and may never get fulls aturation

Question 18

Oxygen carrying capacity of blood

Answer 18

Hemoglobin = 15Hb/dL
1 g Hb binds 1.34 mL of O2
20.1 mL O2/dL blood = oxygen content of arteriole blood

Question 19

O2 saturation is ratio of…

Answer 19

)2 content (amount actually bound) over O2 capacity (usually 98%)
Ratio of how much is bound to what the capacity is

Question 20

Bohr Effect

Answer 20

Inc H+ combines with Hb changing its shape so oxygen cant bind

Question 21

Increase in PCO2 causes…what with pH

Answer 21

Decrease in pH

Carbonic anahydrase causes CO2 and water to combine reversibly and form H2CO3 that then ionizes H+ and HCO3-

Question 22

Increasing temperature…

Answer 22

Decreases tendency for oxygen to remain bound to hemoglobin

Question 23

BPG released by…

Answer 23

RBCs as they break down glucose for energy
Lowers affinity for O2
Binds to hemoglobin and increases release of O2
Increased with anemia, chronic hypoxia, and acclimatization to altitude

Question 24

Oxygen content is critical factor affecting…

Answer 24

metabolism

Question 25

Anemia

Answer 25

Dec. in RBCs Can have normal PO2 and SO2 but a dec oxygen content O2 content and O2 capacity are both decreased, so the ratio stays the same

Question 26

Carbon Monoxide

Answer 26

Affinity of Hb for CO is 210X that of O2 No feedback mechanism when O2 is low CO shifts curve to the left - dec in O2 unloading at the tissues

Question 27

CO2 transport in blood

Answer 27

Dissolved = 7% Bound to Hb = 23% Bicarbonate = 70%

Question 28

CO2 diffusion along pulmonary capillary

Answer 28

46 mmHg to 40 mmHg as you go across pulmonary capillary Takes 1/3 of a sec for CO2 to get to 40 With pathology might not get this, would get to 41 or 42

Question 29

Primary driver for inspiration

Answer 29

CO2 | Just a little change will impact inspiration

Question 30

CO2 Equilibrium - Dissociation Curve

Answer 30

Describes relationship btw PCO2 and CO2 content of the blood | Oxygen helps CO2 diffusion

Question 31

Haldane Effect

Answer 31

Increased PO2 drives the curve down (facilitates unloading of CO2 at the lungs) Decreased PO2 drives curve up (facilitates CO2 loading at the tissues)

Question 32

Integration of Dissociation Curves - blood can carry more....

Answer 32

Blood can carry more CO2 than O2

Question 33

Integration of Dissociation Curves

Answer 33

Shape of CO2 equilibrium curve allows lungs to unload lots of CO2 with small change in PCO2 Change in CO2, large change in content O2 change, not much impact on content