McArdle ch. 13/ Guyton ch.40

Question 1

what is the ventilation perfusion ratio=?

Answer 1

Va/Q

Va=alveolar ventilation rate
Q= rate of pulmonary blood flow

Question 2

Explain the concept of physiologic dead space

Answer 2

has sufficient Va(air) but Q(cardiac output)
the way how i think of it is that: the physiologic dead space is at the top of the lungs where the blood is sent at the bottom of the lungs so theres enough air but no blood to do the exchange with

Question 3

explain the concept of physiologic shunt

Answer 3

when Va/Q is below normal since theres an inadequate amount of Va(air) bc all the blood is sent at the bottom of the lungs theres little air but lots of blood so low ventilation perfusion.
def: certain fraction of venous blood passes though pulmonary capillaries without getting oxygenated.

Question 4

the greater the physiologic shunt the ____ the amount of blood that fails to be oxygenated as it passes through the lungs

Answer 4

greater

Question 5

explain how in different areas in the lungs are different when it comes to the ventilation perfusion ratio

Answer 5

at the top of the lungs: VA/Q is 2.5x greater that as the ideal value = physiological dead space (i.e. more alveoli are being ventilated than perfused)

at the bottom of the lungs:there is too little ventilation in relation to blood flow, VA/Q is as low as 0.6x the ideal value. In this area, a small fraction of the blood fails to become normally oxygenated = physiological shunt

Question 6

During exercise:Better blood flow to the top of the lung = physiological dead space is ____

Answer 6

decreased

since theres more blood flow so more blood getting to the top of the lungs

Question 7

what does the bodys supply of oxygen depend on?

Answer 7

• Concentration of ambient air
  20. 9% O2, 78.6% N2, 0.04% CO2
• Pressure of ambient air

Question 8

Once alveoli are ventilated with fresh air, next step in respiratory process is ____ of O2 from alveoli into pulmonary blood and diffusion of CO2 in opposite direction

Answer 8

diffusion

Question 9

what is diffusion?

Answer 9

random motion of molecules

Question 10

gas pressures are caused by?

Answer 10

Caused by impacts of moving molecules against surface

Question 11

what is the relationship with impacts of gas molecules and pressure

Answer 11

More impacts = higher pressure

Question 12

what is the relationship with the movement of gas molecules and pressure?

Answer 12

The faster the movement, the higher the pressure

Question 13

what is the pressure caused by each gas alone?

Answer 13

partial pressure(Px)
ex: PO2, PN2,...

Question 14

Diffusion rate of each gas is _____ proportional to its partial pressure gradient (concentration)

Answer 14

directly

Question 15

what is Total gas pressure?(daltons law)

Answer 15

a mixture of gases (Ptot) equals the sum of the partial pressures of all gases

Dalton’s Law: Ptot = PO2 + PN2 + PCO2 + Pother

Question 16

what is the air pressure at sea level?

Answer 16

760 mmHg

Question 17

Gas dissolved in water and tissues exerts its own ___ ___ on surface of membrane in same way as gas does in gas phase

Answer 17

partial pressure

Question 18

what is partial pressure of a dissolved gas determined by? (2)

Answer 18

concentration and solubility

Question 19

what the partial pressure equation?

Answer 19

PP= [dissolved gas]/ solubility coefficient

Question 20

what is henry’s law?

Answer 20

The mass of a gas

that dissolves in a fluid at a given temperature varies in direct proportion to the pressure of the gas over the liquid

Question 21

what are the factors that govern the rate of gas diffusion into a fluid?

Answer 21

• The pressure differential between the gas above the fluid and the gas dissolved in the fluid
• The solubility of the gas in the fluid.

Question 22

explain the solubility coefficient:

Answer 22

• Measure of electro-chemical attraction that a dissolved gas has to water molecules
• High attraction = high solubility of gas, i.e more gas molecules can be dissolved before partial pressure of that gas within the solution increases

Question 23

what is the difference between CO2 and O2 solubility?

Answer 23

CO2 is 24 times more soluble than O2 in fluid

O2: 0.024
Co2:0.57

Question 24

what are the factors that affect the diffusion rate through a respiration membrane?

Answer 24

D proportional to:

change in P* cross sectional area * solubility / distance * sqrt(molecular weight)

Question 25

what is diffusion coefficient?

Answer 25

solubility / sqrt(molecular weight)

Question 26

what are the layers of respiratory membrane?

Answer 26

- Fluid and surfactant layer (in alveolar lining) - Alveolar epithelium composed of epithelial cells - Alveolar epithelial basement membrane - Thin interstitial space between alveolar epithelium and capillary membrane - Capillary basement membrane - Capillary endothelial membrane

Question 27

what does oxygen concentration and partial pressure of O2 in alveoli depend upon?

Answer 27

-Alveolar ventilation (rate of new O2 inspired into alveoli) Increase of alveolar ventilation increases O2 concentration (CAO2) and PAO2 -Rate of absorption of O2 into blood Increase of O2 absorption rate decreases CAO2 and PAO2

Question 28

If O2 absorption increases to 1000 ml/min (as during moderate exercise), __times increase in VA required to maintain same PAO2

Answer 28

4x

Question 29

the Co2 concentration and PCo2 in alveoli depends upon?

Answer 29

-Excretion rate of CO2 from pulmonary arterial blood into alveoli Increase of CO2 excretion rate increases CACO2 and alveolar PACO2 -The rate of alveolar ventilation to expire CO2 Increase of ventilation rate decreases the alveolar PACO2 and CO2 concentration (CACO2)

Question 30

what is ambiant air?

Answer 30

Partial pressures of gases in dry ambient air at sea level PO2 = 159 mm Hg, PCO2 = 0.2 mm Hg, PN2 = 600 mm Hg

Question 31

what is tracheal air?

Answer 31

- Air completely saturates with water vapor as it enters the nasal cavities/mouth and passes down the respiratory tract - The effective PO2 in tracheal air decreases by about 10 mm Hg from its ambient value of 159 mm Hg to 149 mm Hg - Carbon dioxide’s negligible contribution to inspired air means that humidification exerts little effect on inspired PCO2

Question 32

what is alveolar air?

Answer 32

- Alveolar air composition differs from the incoming breath of moist ambient air because CO2 continually enters the alveoli from the blood: 14.5% O2, 5.5% CO2, and 80.0% N2 - Average pressures exerted by O2 and CO2 against the alveolar side of the alveolar–capillary membrane: PO2 = 103 mm Hg, PCO2 = 39 mm Hg

Question 33

O2 travels from a ___ to lower pressure as it dissolves and diffuses through the alveolar membranes into the blood

Answer 33

higher

Question 34

CO2 exists under a slightly ____ pressure in returning venous blood than in the alveoli, causing net diffusion of CO2 from the blood into the lungs

Answer 34

greater

Question 35

N2 is ___ in alveolar–capillary gas

Answer 35

unchanged

Question 36

what are the factors that impair gas transfer capacity at the alveolar capillary membrane?

Answer 36

- Buildup of a pollutant layer that “thickens” the alveolar membrane - Reduction in alveolar surface area - Low perfusion

Question 37

explain the concept of slow replacement of alveolar air?

Answer 37

-Average functional residual capacity (FRC) ~ 2300 ml Yet only ~350 ml of new air per normal resting breath is brought into alveoli - Means that only ~ 1/7 of total air remaining in lungs is replaced with new air with each breath - Rate of removal of excess gas from alveoli depends on rate of alveolar ventilation (VA) - Slow replacement is important in preventing sudden changes in gas concentrations in blood -> stabilizes respiratory control mechanisms

Question 38

Net rate of diffusion in fluids is affected by pressure difference + several other factors:

Answer 38

- Solubility of gas in fluid - Cross-sectional area of fluid - Distance through which gas must diffuse - Molecular weight of gas - Temperature of fluid (in body, remains constant)

Question 39

explain the gas transfer in tissues:

Answer 39

- At rest, PO2 in the fluid outside a muscle cell averages 40 mm Hg and intracellular PCO2 averages 46 mm Hg - In vigorous exercise, PO2 within muscle tissue falls toward 0 mm Hg, the PCO2 approaches 90 mm Hg - Pressure differences between gases in plasma and tissues establish diffusion gradients - O2 leaves the blood and diffuses toward cells, while CO2 flows from cells into the blood - Blood then passes into the venous circuit for return to the heart and delivery to the lungs