PHGY 216 - MODULE 3 RESPIRATORY SYSTEM
REVIEW
Gas Exchange (definition & composition) - Answers - diffusion of O2 from alveoli into
blood & CO2 from blood into alveoli
- occurs along pressure gradient between partial pressures of alveoli (Pa) & pulmonary
artery (Pv ~ mixed venous blood), along with resistance to diffusion
Ventilation - Answers - provides O2 for alveoli into blood & expires CO2 from blood into
atmosphere; gas movement driven by diffusion & partial pressure grads (TV > ADS)
*PO2 only accounts for unbound/free-flowing oxygen
Factors affecting Resistance to Diffusion (3) - Answers - 1. Membrane Surface Area (A)
2. Membrane Thickness (T)
3. Gas Diffusibility (D, constant value so ignored)
Gas Volume EQN - Answers - Volume Gas = (P alveoli - P venous artery) x
(AREA/THICKNESS)
Partial Pressure (definition & daltons law relationsip) - Answers - pressure that would be
exerted by one particular gas in a mixture, if it occupied the same volume by itself
DALTON's LAW = pressure exerted by gas in a mixture is directly proportional to the
percentage of that gas in the mixture
Factors determining amount of gas that can dissolve in a liquid (2) - Answers - 1. Partial
Pressure in Air (greater PP = greater vol. gas driven into liquid)
2. Solubility of Liquid (the more soluble a gas is in liquid = the more gas that will
dissolve)
Alveolar Partial Pressure in Lungs (rule & composition values) - Answers - produced
alveolar air DOES NOT have same composition/PP as inspired air due to water vapour
saturation & anatomical dead space
*@body temp: P H2O-V = 47mmHg, P N2 = 563mmHg, PO2 = 150mmHg (79:21%)
*JUST BEFORE LUNGS: PvO2= 40mmHg, PvCO2 = 46mmHg
IN LUNGS:
PaO2 = 100mmHG
PaCO2 = 40mmHG
, Alveolar Gas EQN (PaO2 = ?; theory) - Answers - PaO2 = PiO2 - PaCO2/R
(Alveoli Partial Pressre = P of inspired oxygen (150mmHg) - P of alveolar CO2
(40mmHg)/Respiratory Quotient (~ 0.8 = co2 formation : oxygen consumption)
*only 350/500mL is moved in/out, with the remaining 150mL being mixed gases; at end
of alveolar inspiration, only 15% is "fresh air", causing further PaO2 drop to ~100mmHg
- low amount of fresh air circulation & fast diffusion rate causes PaO2/CO2 to remain
~constant
Conc. of Blood-Dissolved Gases (CO2 vs O2 when entering & leaving lungs) - Answers
- *CO2 is 20x more soluble than O2 in blood, meaning even if PP were equal, CO2 conc
>)
O2: entering lungs = 40mmHg = 150ml O2/L, leaving lungs = 100ml O2/L (150ml =
reserve vol., 50mL removed)
CO2: entering lungs = 46mmHg = 520ml CO2/L
leaving lungs = 40mmHg = 480ml CO2/L
*not a big difference due to responsibility to maintainn acid-base balance
Factors affecting Gas Exchange (3) - Answers - *ALSO STRONGLY DRIVEN BY
TISSUE METABOLISM
1. SURFACE AREA: the greater the surface area = the greater amount of gas that can
be exchanged (i.e. pulmonary capillaries are typically closed but during exercise,
Pcapillaries open to increase SA for gas exch.)
2. MEMBRANE THICKNESS: increase in membrane thickness b/w alveoli & blood =
decreased/less efficient permeability = decrease gas exch. (i.e. mucous secreting lung
disease/asthma)
3. CAPILLARY TRANSIT TIME: amount of time that pulmonary capillary blood is
exposed to alveolar gas (as gas can only be exchanged during this time/upon exposure)
is impacted by flow rate; @REST = blood remains in Pcapillaries for 0.75sec vs 0.4
during exercise (exchange takes ~0.25)
GAS EXCHANGE DIAGRAM - Answers -
Haemoglobin (Hb) - Answers - iron-bearing protein found in RBC that binds & carries
gas molecules using its 4 iron subunits; transports 98.5% of circulating O2 to act as a
reserve
*Hb is fully saturated when all Hb molecules present are carrying the maximum # of
oxygen molecules (% saturation = highly dependent on P O2)
REVIEW
Gas Exchange (definition & composition) - Answers - diffusion of O2 from alveoli into
blood & CO2 from blood into alveoli
- occurs along pressure gradient between partial pressures of alveoli (Pa) & pulmonary
artery (Pv ~ mixed venous blood), along with resistance to diffusion
Ventilation - Answers - provides O2 for alveoli into blood & expires CO2 from blood into
atmosphere; gas movement driven by diffusion & partial pressure grads (TV > ADS)
*PO2 only accounts for unbound/free-flowing oxygen
Factors affecting Resistance to Diffusion (3) - Answers - 1. Membrane Surface Area (A)
2. Membrane Thickness (T)
3. Gas Diffusibility (D, constant value so ignored)
Gas Volume EQN - Answers - Volume Gas = (P alveoli - P venous artery) x
(AREA/THICKNESS)
Partial Pressure (definition & daltons law relationsip) - Answers - pressure that would be
exerted by one particular gas in a mixture, if it occupied the same volume by itself
DALTON's LAW = pressure exerted by gas in a mixture is directly proportional to the
percentage of that gas in the mixture
Factors determining amount of gas that can dissolve in a liquid (2) - Answers - 1. Partial
Pressure in Air (greater PP = greater vol. gas driven into liquid)
2. Solubility of Liquid (the more soluble a gas is in liquid = the more gas that will
dissolve)
Alveolar Partial Pressure in Lungs (rule & composition values) - Answers - produced
alveolar air DOES NOT have same composition/PP as inspired air due to water vapour
saturation & anatomical dead space
*@body temp: P H2O-V = 47mmHg, P N2 = 563mmHg, PO2 = 150mmHg (79:21%)
*JUST BEFORE LUNGS: PvO2= 40mmHg, PvCO2 = 46mmHg
IN LUNGS:
PaO2 = 100mmHG
PaCO2 = 40mmHG
, Alveolar Gas EQN (PaO2 = ?; theory) - Answers - PaO2 = PiO2 - PaCO2/R
(Alveoli Partial Pressre = P of inspired oxygen (150mmHg) - P of alveolar CO2
(40mmHg)/Respiratory Quotient (~ 0.8 = co2 formation : oxygen consumption)
*only 350/500mL is moved in/out, with the remaining 150mL being mixed gases; at end
of alveolar inspiration, only 15% is "fresh air", causing further PaO2 drop to ~100mmHg
- low amount of fresh air circulation & fast diffusion rate causes PaO2/CO2 to remain
~constant
Conc. of Blood-Dissolved Gases (CO2 vs O2 when entering & leaving lungs) - Answers
- *CO2 is 20x more soluble than O2 in blood, meaning even if PP were equal, CO2 conc
>)
O2: entering lungs = 40mmHg = 150ml O2/L, leaving lungs = 100ml O2/L (150ml =
reserve vol., 50mL removed)
CO2: entering lungs = 46mmHg = 520ml CO2/L
leaving lungs = 40mmHg = 480ml CO2/L
*not a big difference due to responsibility to maintainn acid-base balance
Factors affecting Gas Exchange (3) - Answers - *ALSO STRONGLY DRIVEN BY
TISSUE METABOLISM
1. SURFACE AREA: the greater the surface area = the greater amount of gas that can
be exchanged (i.e. pulmonary capillaries are typically closed but during exercise,
Pcapillaries open to increase SA for gas exch.)
2. MEMBRANE THICKNESS: increase in membrane thickness b/w alveoli & blood =
decreased/less efficient permeability = decrease gas exch. (i.e. mucous secreting lung
disease/asthma)
3. CAPILLARY TRANSIT TIME: amount of time that pulmonary capillary blood is
exposed to alveolar gas (as gas can only be exchanged during this time/upon exposure)
is impacted by flow rate; @REST = blood remains in Pcapillaries for 0.75sec vs 0.4
during exercise (exchange takes ~0.25)
GAS EXCHANGE DIAGRAM - Answers -
Haemoglobin (Hb) - Answers - iron-bearing protein found in RBC that binds & carries
gas molecules using its 4 iron subunits; transports 98.5% of circulating O2 to act as a
reserve
*Hb is fully saturated when all Hb molecules present are carrying the maximum # of
oxygen molecules (% saturation = highly dependent on P O2)
