Gaz exchange Flashcards
Alveoli
-basement membrane (outer layer)
-epithelial cells:
pneumocytes type 1
pneumocytes type 2 (bigger less frequent)
-surfactant layer
outside alveoli: duct. bronchial epithelium: ciliated epithelial (columnar) cells (most present), club cells (larger/more rectangular), globet cells (hook head), clara cells (near cilia), cilia
interstitial tissue between alveoli and blood vessel: can become very thin making the exchange easier
Solubility
O2 is soluble
CO2 is even more soluble
Gaz exchange
Oxygen, nitrogen, carbon dioxide: move passively
Blood arriving to heart (right side) is deoxygenated PCO2 >PO2. Venules -> vein -> inferior/superior vena cava
Heart pump blood to lung through pulmonary artery
oxygenated blood goes back to heart through pulmonary veins PO2>PCO2.
Heart pump blood to tissues through aorta
Some O2 from plasma to tissues 3%
Most in rbc on the 4 binding sites of hemoglobin 97%
some CO2 fromm interstitial fluid to blood plasma 10%
OR most CO2 associate with H20 and transported as bicarbonate HCO3- + H+. 70% Happens slowly in blood plasma or fast in red blood cells CA.
H+ can combine with Hemoglobin to form HHb
OR some CO2 enter red blood cells and bind to Hb to form HbCO2 (carboamino acid) 20%
CO2 up -> pH down. CO2 down -> pH up
The chloride shift is an exchange of ions that takes place in our red blood cells in order to ensure that no build up of electric change takes place during gas exchange.
Gaz exchange occurs while blood pass through capillary. Most happen in first 1/3 of normal gaz exchange which allows a speed increase
Oxygen hemoglobin saturation curve
x axis: PO2 y axis: saturation % S shaped PO2 from 0 to 104mmHg Saturation from 0 to a 100
from ~60 to 104mmHg there is a plateau phase. Means that even with a lower or higher PO2 saturation is mostly the same. This shows hemoglobin is an oxygen buffer: support high pressure of deep sea and low pressure of high altitude
First slow curve then very fast: once 1 O2 bind to Hb it increases the affinity
Can now how much oxygen was unloaded by taking starting saturation ~98% and end saturation (can look from the PO2 mmHg). => steep slope, more O2 unloaded: useful for exercise !!
Steep slope allow high delivery. PO2 down, BF up
15-40mmHg most O2 is delivered.
curve more to the right: more acidic. pH down
curve more to the left: less acidic. pH up
Bohr effect
Shift saturation curve to the right: more acidic, pH down
H+, CO2, Temp, 2.3 BPG: up
=> O2 affinity down => more O2 unloaded
metabolic activity increase temperature and CO2
exercise increase temperature
Haldane effect
Shift saturation curve to the left: less acidic, pH up
H+, CO2, Temp, 2.3 BPG: down
=> O2 affinity up => less O2 unloaded
CO present
Air composition
The altitude does not change the composition but the density
atmosphere:
78% nitrogen, 21% oxygen, 1% argon, < CO2, other gazes
exhaled:
CO2, water up. O2 down
alveolar:
humidity makes the partial pressures go down. Residual capacity means the air is slowly replaced (important for no sudden changes in concentrations). CO2 up.
Respiratory membrane
speed depends on thickness membrane, surface area: bigger diffusion up, diffusion coefficient CO2 20 higher O2, partial pressure difference
alveoli: surfactant layer, epithelium, basement membrane.
interstitial space
capillary: basement membrane,endothelial cells
interstitial space very thin or the 2 membranes fuse
Diffusing capacity incrase during exercise. Volume of gaz in 1min. CO2 hardly changes as it diffuse fast already.
Exercise -> open more capillaries and vasodilation -> surface area increase -> speed increase. + match ventilation and perfusion
Pressure difference
tendency of gaz to move through membrane
High PO2 alveoli -> Low PO2 capillaries.
High PCO2 capillary -> low PCO2 alveoli
depends on blood flow
PO2 alveoli=104mmHg
PO2 venous=40mmHg
=> 64mmHg O2 exchanged before passing whole capillary
Exercise-> blood in capillary time reduced
PO2 capillaries=95mmHg
PO2 tissues=40mmHg
55mmHg O2 exchanged. BF up O2 up. tissues consume O2
O2 used -> CO2-> gaz diffusion in opposite direction
PaCO2=45mmHg tissues produce CO2
PCO2=40mmHg
Pressure gradient of CO2 lower than O2 but solubility higher so the diffusion is the same.
PAO2 alveoli=104mmHg < PO2 inspired 160 mmHg. O2 goes to alveoli
PACO2 = 40 mmHg > PCO2 0 mmHg CO2 goes out of alveoli
Partial pressures reflect the metabolic activity
Dalton law
high to low concentrations
sum partial pressures all gaz = total pressure
Pb time fractional pressure. If humidity substract PH20
Fick law
net rate of diffusion V
proportional to partial pressure in alveolar sacs PA and in blood Pa. proportional to surface area A and Flow of the gaz. Inversely proportional to wall thickness T.
V=(PA-Pa)ADFlow/T
D is diffusion coefficient
Boyle’s law
pressure and volume are inversely proportional
if volume goes up, pressure goes down
if volume goes down, pressure goes up
Inspiration: lung volume up->alveolar pressure down. Air gets in (pressure gradient, high to low pressure). CO2 dissolved in gazeous. CO2 down -> gradient down -> harder gaz exchange
Expiration: lung volume down->alveolar pressure up-> air gets out (pressure gradient, high to low pressure). O2 up -> concentration gradient up -> gaz exchange more efficient.
Ventilation and perfusion
perfusion: blood flow in capillaries
ventilation: amount of gaz reaching the alveoli
alveoli:
PO2 up: capillaries dilate: blood pick up O2
CO2 down: bronchioles constrict: no need to remove CO2
PO2 down: capillaries constrict, not a lot of O2 to pick
CO2 up: bronchioles dilate: CO2 needs to be removed
PCO2: controles bronchodilation: ventilation
PO2: controles vasoconstriciton: perfusion
Oxygen transport
- 5% dissolved in plasma
- 5% bound to hemoglobin: 4 binding sites
hemoglobin affinity to CO > affinity to O2. O2 replaced by CO -> O2 can’t be replaced anymore. Brain and tissue O2 down
treatment: 100% oxygen
Hypoxic vasoconstriction
alveolar hypoxia -> intrapulmonary arteries constrict -> divert blood to oxygenated lung regions -> diffusion up->ventilation and perfusion balance
happens in altitude
