Intro Flashcards
Type of cells at respiratory epithelium?
Pseudostratefied columnar epithelium
Goblet cells
Make mucus
Type II pneumocytes
Divide to become type II pneumocytes, but also make surfactant
Difference between bronchus histology and bronchiole histology
Bronchus is cartilagenous.
Bronchiole is noncartilagenous
Blood air barrier
Fused basement membranes of alveolus and capillary.
Interstitium
Space between epithelial basement membrane and vascular basement membrane.
Type I pneumocytes
Cover 95% of the surface area but only represent 40% of the cells. Cannot divide
Type II pneumocytes
Cover 5% of the surface area but account for 60% of the cells
Pulmonary vasculature
Is dual:
Pulm arteries: low pressure, has capacitance, gas exchange
bronchial arteries: systemic pressure, supply nutrients to parenchyma.
Structure of pulmonary arteries
Thinner and wider than systemic counterparts due to low pressure
How does size of particulate matter from environmental exposure matter?
Greater than 10 microns get filtered in nose/nasopharynx
5-10 microns get trapped in mucous coating in airways
<2 microns can reach alveolar air spaces.
Minute respiration = ?
Tidal volume * RR
Vt * RR
Normal tidal volume?
450-500 ml
Normal RR is 12-14 breaths/minute
Normal minute ventilation
~6 liters/min
Alveolar respiration = ?
Minute ventilation - dead space ventilation
or
Va = (Vt-Vd) * RR
Physiologic dead space?
The total volume of lungs that does not participate in gas exchange.
Equals anatomic dead space (structures north of respiratory bronchioles) and functional dead space (any alveoli that arent participating in gas exchange)
Normally physiologic dead space = anatomic dead space.
How to measure dead space?
Assuming that arterial CO2 is equal to alveolar CO2…
Vd = Vt * [(PaCO2-PeCO2)/PaCO2]
Relationship between alveolar ventilation and alveolar CO2 content assuming production of CO2 is constant.
Inverse relationship of alveolar ventilation and alveolar CO2 content.
Breathe more, alveolar CO2 decreases. Breathe less, alveolar CO2 increases
Equation for relating alveolar ventilation to partial pressure of alveolar CO2
Va = (VCO2 * K) /PACO2
What happens if the production of CO2 doubles?
Ventilation will increase to maintain PACO2
What does the alveolar gas equation describe?
Describes the relationship between alveolar PCO2 and PO2
Alveolar Gas Equation
PAO2 = PIO2 - (PACO2/R)
R=0.8
Why is R=.8 in the alveolar gas euqation
Because rate of CO2 production is only 80% the rate of O2 consumption
How to determine alveolar concentration of CO2?
Assume its equal to the partial pressure of CO2 in the arterioles.
Regional differences in ventilation?
Lungs are more compliant at bottom and can utilize the weight of the lungs to squeeze more air out. Least ventilation ot that top
Regional differences in perfusion
At top of lungs Palveoli>Parterioles>Pveins, so decrease in perfusion.
Middle Parterioles>Palveoli>Pveins so slight increase in perfusion
Bottom Parterioles>Pveins>Palveoli because gravity.
Regional differences in V/Q
V/Q highest at top because Q is so low
V/Q lowest at bottom because Q is so high.
The slopes of the lines are different. Regional variations in perfusion are huge.
In what zone is PaO2 highest?
Zone 1. PaCO2 is opposite to PaO2.
Overall V/Q ratio for lung?
0.8. Alveolar ventilation is 80% of pulmonary blood flow.
High V/Q ratio means
More ventilation relative to perfusion. There is a blockage (DEAD SPACE). Ventilation w/o perfusion ie PE. V/Q can be infinity. Air coming from this area will have high O2 content.
Low V/Q means
High perfusion relative to ventilation. This can be caused by an airway obstruction or a cardiac shunt. Blood coming from this area will have a low O2 and a high CO2.
PIO2 =
(Pb-PH2O) * Concentration of O2 in inspired air.
Alveolar air o2 and co2 content
O2 = 100
Co2=40
Mixed venous blood o2 and co2 content
O2=40
Co2=46
Systemic arterial blood o2 and co2 content
100
40
Fick’s law of diffusion
Rate of transfer of a gas by diffusion is proportional to the driving force (partial pressure), diffusion coefficient, surface area available. All of this divided by thickness of the membrane barrier.
Perfusion limited gas exchange
total amount of gas transported is limited by the amount of blood coming through because it diffuses rapidly. Partial pressure gradient won’t be maintained because of rapid equilibration, so need to bring more deoxygenated blood to drive diffusion.
Gases that are perfusion limited
O2, CO2. Pressure equilibrates in first 1/3 of capillary.
How does the pressure gradient diminish for O2?
Even though O2 is binding to hemoglobin, Hb can be saturated, so O2 goes into solution. When blood PaO2 reaches PAO2, transfer stops.
Diffusion limited gas exchange
Total amount of gas transported across barrier is limited by diffusion process. Pressure gradient is always maintained. For example, CO, immediately picked up by hemoglobin, doesn’t dissolve in blood.
What is diffusion limited
CO
O2 during exercise (because CO increases and brings a lot more hemoglobin).
Concentration of O2 in blood=
C = Po2 * solubility
Solubility of blood is 0.003
How much total O2 content is bound by Hb
98%
