lecture 26 Flashcards
what is air composed of?
78% N2,
21% O2,
0.033% CO2
Dalton’s Law definition
the total pressure exerted by a mixture of gases is the sum of pressures exerted by all individual gases
partial pressure
the pressure exerted by an individual gas
total air pressure, Patm= …. (all gases)
Pn2+ Po2 + Pco2
in humid air, Patm= … (all gases)
Pn2+ Po2+ Pco2 +Ph2o
in dry air Pgas= Patm*…
Patm*% of gas in atmosphere
in humid air, Pgas= (Patm…)*…
(Patm-Ph2o)*% gas in atmosphere
as alveolar ventilation increases, — increases and — decreases
Po2 increases and Pco2 decreases
in the atmosphere, Po2=?
160 mm Hg
in the atmosphere, Pco2=?
0.25 mm Hg
in the alveoli, Po2=?
(normal quiet breathing)
100 mm Hg
in the alveoli, Pco2=?
(normal quiet breathing)
40 mm Hg
alveolar partial pressures can vary with..
hypoventilation or hyperventilation
match perfusion with ventilation (explain)
perfusion= blood flow through organs and tissues
ventilation= breathing
the rate is matched, v efficient system
100 mm Hg in alveoli= 100 mm Hg in capillary blood
if you hypoventilate… (Po2 and Pco2)
v slow brething
Pco2 rises in alveoli
Po2 falls off
if you hyperventilate… (Po2 and Pco2)
v fast breathing
Pco2 falls off because you keep expelling it
Po2 rises because you keep pulling in o2
How does O2 enter alveoli/circulation?
-at a thin interface
-type I alveolar cells are for exchange
- O2 transported to heart
(98% attached to Hb in RBC, rest dissolved gas in plasma)
- O2 dropped of and used for cell resp.
what happens after O2 is used for cell resp. (byproduct?)
- used to create ATP.
- a byproduct of cell resp is CO2
- Co2 is transported as bicarbonate (HCO3-) or dissolved + bound to Hb
- CO2 is dropped in the lungs and expelled
What cellular barriers to O2 and CO2 have to diffuse across?
alveolar epithelial cells and capillary endothelial cells
(2 cells, 4 membranes)
-apical and basolateral membranes
Fick’s Law
greatest flux= high concentration (partial pressure) gradient
big distance= lower flux
–> diffusion rate proportional to: ADdeltaP/T^2
small change in T (thickness)= really big change in rate
rate of diffusion is directly proportional to (3 things)
- surface area (A)
- membrane permeability (D= diffusion constant)
- concentration (partial pressure) gradient
rate of diffusion is inversely proportional to
diffusion distance (T)
what is T in Fick’s Law?
diffusion distance
- membrane thickness
- interstitial fluid
what patterns does air follow in terms of flow between atmosphere and alveoli?
air moves by bulk flow between atmosphere and alveoli
diffusion reaches — under normal circumstances
equilibrium
in pulmonary circulation, what is alevolar and venous blood Po2 and Pco2?
pulmonary= deoxygenated
Alveolar Po2 > venous blood Po2
Alveolar Pco2 < venous blood Pco2
in systemic circulation, what is arterial and tissue Po2 and Pco2?
systemic= oxygenated blood
arterial Po2 > tissue Po2
arterial Pco2 < tissue Pco2
3 factors that affect gas exchange
- gas diffusion between alveoli and blood
- adequate perfusion of alveoli
- O2 reaching the alveoli
–> alveolar ventilation (hypo/hyper, decreased due to mucus)
–> composition of inspired air (sea level vs. mntn top)
perfusion
the process of blood flowing to the alveoli of the lungs through capillaries
ineffective gas exchange leads to
low O2 content in blood
hypoxia= not enough O2 to meet body’s needs
2 factors that decrease the amount of O2 reaching the alveoli
- low O2 content in the atmosphere
- low alveolar ventilation
- decreased lung compliance (cold, bronchitis…)
- increased airway resistance
- CNS depression (drugs, alcohol overdose)
lung compliance
how easily they expand to accommodate a new volume
(no “snap back”)
conditions that cause hypoxia?
emphysema
asthma
fibrotic lung disease
pulmonary edema
emphysema
decreased SA
decreased Po2 (pp gradient)
= lower rate of diffusion, ineficient O2 uptake
asthma
=excessive bronchoconstriction
increased resistance
decreased flow
–> less O2 getting in lungs
fibrotic lung disease
= scar tissue building up around alveoli
- increased thickness
- decreased Pco2 (pp gradient)
- reduce compliance
–> decrease O2 coming in
pulmonary edema
interstitial fluid (buildup of fluid in interstitial space, in between type I and epithelial cells)
–>increased distance (d^2, mild cases greatly affect diffusion)
- seen in heart failure, fluid builds up)
