Gas Exchange + Transport: O2 Flashcards
how do gases move in the alveoli and capillaries
gases move down concentration gradients by diffusion (same as pressure gradients)
what is gas partial pressures
air is a mixture of gases each of which exerts its own partial pressure (P) is independent of other gases
the total pressure is the sum of the partial pressure of each gas in the mixture Dalton’s law
what alters the partial pressure of O2
alters depending on other factors ex. atmospheric pressure (Patm)
how can PO2 be calculated
PO2 = Patm x Fo2
Patm = mmHg
Fo2 = mole fractional concentration of oxygen in air
what occurs to PO2 in the presence of water vapour molecules
reduces concentration of O2
PO2 is less in humidified air
how is PO2 of humidified gas in airways calculated
PO2 = (Patm - Ph2o) x FinhaledO2
where does gas exchange occur
in alveoli
what is the respiratory unit
airways branch into smaller and more numerous bronchioles until terminating to a group of alveoli
each division results in an increase in #, decrease in diameter, increase in surface area
- resp bronchioles
- alveolar ducts
- alveoli
what are the characteristics of alveoli
- large surfae area (~100m^2)
- very thin walls
identify the gas exchange structures
what is the pulmonary circuit
O2 enters blood
CO2 leaves
what is the systemic circuit
O2 leaves blood
CO2 enters
what is the difference between O2 and CO2 pressure gradient
pressure gradient for O2 is much bigger than for CO2
what are the partial pressures of gas gradients
how is O2 carried in the blood
- dissolved (measured clinically in arterial blood PaO2) –> very small %
- bound to hemoglobin (Hb)
what factors affect oxygen transport
- concentration of pigment
- rate of circulation (cardiac output)
- O2 affinity of pigment
what is the concentration of pigments in oxygen transport
birds and mammals 15-20ml/100
lower in invertebrates with Hb 4-6ml/100ml
how does rate of circulation affect oxygen transport
circulatory system of mammals and birds operates at leisurely pace at rest
during exercise O2 demand increases so circulatory system responds
rate of O2 delivery = cardiac output x (arterial [O2] - venous [O2])
increase in rate of blood flow + increase extraction of O2 = increase in O2
venous blood becomes much more deoxygenated than at rest
what does degree of Hb oxygenation depend on
PO2
at high PO2 –> promotes O2 binding
at low PO2 –> reduces binding
how does oxygen affinity of pigments affect oxygen transport
pigments that bind O2 at low PO2 = high affinity
pigments that require higher PO2 to bind to O2 = low affinity
what is human Hb affinity for O2
relatively low affinity for O2
why does human Hb have a low affinity for O2
lower affinity means O2 more difficult to bind to pigment but easier to release O2
what factors affect O2 affinity
- pH and CO2 (Bohr effect)
- temperature
- ions
- organic compounds
what is the bohr effect
oxygen affinity depends on the PCO2 and the pH
a decrease in pH or increase in PCO2 = decrease in O2 affinity
shifts the saturation curve right
how does the bohr effect enhance O2 delivery
the bohr shift lowers affinity at tissues to increase O2 release
shifts back to higher affinity at lungs/gills to promote O2 uptake
how does temperature affect O2 affinity
increase in temp decreases O2 affinity
enhance O2 delivery to muscles similar to bohr effect
how does inorganic ions affect O2 affinity
ions in the blood can allosterically modulate O2 affinity of respiratory pigments
Cl ions in RBCs critical allosteric modulator
how do organic compounds affect O2 affinity
2,3-diphosphoglycerate (DPG) reduces O2 affinity of Hb molecules it binds
human Hb continuously exposed to 2,3-DPG so constantly modulated by a normal DPG level
2,3-DPG is increase by chronic hypoxia, anemia and acclimation to high altitude
what is cooperativity
binding at one site increases affinity at remaining sites
partially oxygenated Hb more likely to bind O2 than fully deoxygenated molecule
cooperativity enhances the responsiveness to changes in PO2
