McArdle ch. 13/ Guyton ch.40 Flashcards
what is the ventilation perfusion ratio=?
Va/Q
Va=alveolar ventilation rate
Q= rate of pulmonary blood flow
Explain the concept of physiologic dead space
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
explain the concept of physiologic shunt
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.
the greater the physiologic shunt the ____ the amount of blood that fails to be oxygenated as it passes through the lungs
greater
explain how in different areas in the lungs are different when it comes to the ventilation perfusion ratio
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
During exercise:Better blood flow to the top of the lung = physiological dead space is ____
decreased
since theres more blood flow so more blood getting to the top of the lungs
what does the bodys supply of oxygen depend on?
- Concentration of ambient air
20. 9% O2, 78.6% N2, 0.04% CO2 - Pressure of ambient air
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
diffusion
what is diffusion?
random motion of molecules
gas pressures are caused by?
Caused by impacts of moving molecules against surface
what is the relationship with impacts of gas molecules and pressure
More impacts = higher pressure
what is the relationship with the movement of gas molecules and pressure?
The faster the movement, the higher the pressure
what is the pressure caused by each gas alone?
partial pressure(Px) ex: PO2, PN2,...
Diffusion rate of each gas is _____ proportional to its partial pressure gradient (concentration)
directly
what is Total gas pressure?(daltons law)
a mixture of gases (Ptot) equals the sum of the partial pressures of all gases
Dalton’s Law: Ptot = PO2 + PN2 + PCO2 + Pother
what is the air pressure at sea level?
760 mmHg
Gas dissolved in water and tissues exerts its own ___ ___ on surface of membrane in same way as gas does in gas phase
partial pressure
what is partial pressure of a dissolved gas determined by? (2)
concentration and solubility
what the partial pressure equation?
PP= [dissolved gas]/ solubility coefficient
what is henry’s law?
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
what are the factors that govern the rate of gas diffusion into a fluid?
- The pressure differential between the gas above the fluid and the gas dissolved in the fluid
- The solubility of the gas in the fluid.
explain the solubility coefficient:
- 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
what is the difference between CO2 and O2 solubility?
CO2 is 24 times more soluble than O2 in fluid
O2: 0.024
Co2:0.57
what are the factors that affect the diffusion rate through a respiration membrane?
D proportional to:
change in P* cross sectional area * solubility / distance * sqrt(molecular weight)
what is diffusion coefficient?
solubility / sqrt(molecular weight)
what are the layers of respiratory membrane?
- 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
what does oxygen concentration and partial pressure of O2 in alveoli depend upon?
-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
If O2 absorption increases to 1000 ml/min (as during moderate exercise), __times increase in VA required to maintain same PAO2
4x
the Co2 concentration and PCo2 in alveoli depends upon?
-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)
what is ambiant air?
Partial pressures of gases in dry ambient air at sea level PO2 = 159 mm Hg, PCO2 = 0.2 mm Hg, PN2 = 600 mm Hg
what is tracheal air?
- 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
what is alveolar air?
- 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
O2 travels from a ___ to lower pressure as it dissolves and diffuses through the alveolar membranes into the blood
higher
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
greater
N2 is ___ in alveolar–capillary gas
unchanged
what are the factors that impair gas transfer capacity at the alveolar capillary membrane?
- Buildup of a pollutant layer that “thickens” the alveolar membrane
- Reduction in alveolar surface area
- Low perfusion
explain the concept of slow replacement of alveolar air?
-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
Net rate of diffusion in fluids is affected by pressure difference + several other factors:
- 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)
explain the gas transfer in tissues:
- 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
