Gas Transport Flashcards
what are the two ways oxygen is transported in blood
- dissolved in plasma
- bound to hemoglobin (majority)
hemoglobin
heme protein inside RBCs
tetramer - 4 subunits that can each bind O2
how does O2 binding affect binding affinity of other subunits
O2 binding increases binding affinity of other subunits
O2 capacity
the maximum amount of O2 that could be carried by hemoglobin (mL O2 per dL of blood)
O2 capacity = [hgb] x 1.36
Hufner’s constant
average value of mL O2 bound per gram of hgb (not all Hgb are completely filled/bind at max capacity)
1.36 mL/g
O2 saturation
actual measurement of O2 bound to hemoglobin (percentage of actual amount bound vs maximum amount that could be bound
SO2 = [(O2 bound) / (O2 capacity)] x 100
if PCV = 39% (13 g/dl Hgb) and SO2 = 90%, how much O2 is bound?
O2 capacity = 13 x 1.36 = 17.68
O2 saturation = 90% of 17.68 = 15.9 mL/dL
how does anemia affect the O2 binding ability of Hgb
anemia increases O2 binding ability
dissolved O2
measures the amount of O2 dissolved in blood
dissolved O2 = PO2 x solubility coefficient
(PO2 can be measured on blood gas)
henrys law
concentration of a gas = the partial pressure of the gas x solubility constant
solubility coefficient
0.003 mL O2 / dLxmmHg
if PO2 = 100 mmhg, how much O2 is dissolved in plasma
dissolved O2 = 100 x 0.003 = 0.3 mL/dL
what is the importance of dissolved O2
drives diffusion gradients and determines Hgb-O2 saturation
total O2 content
measures the total amount of O2 in the body
C(O2) = (SO2/100 x 1.36 x [Hgb]) + (0.003 x PO2)
sum of the hemoglobin bound and dissolved O2 content
Hb-O2 equilibrium curve
shows the relationship between PO2 and SO2
sigmoidal curve - nonlinear due to heme-heme interactions altering affinity based on O2 binding status
what determines SO2
PO2 (nonlinear)
as PO2 increases, SO2 increases until fully saturated
how are SO2 and C(O2) related
directly related (linear) due to negligible amount dissolved in plasma
can assume total concentration = saturated concentration
where on the curve do animals exist in health
upper end of curve
arterial PO2 = 100, SO2 = 98%
venous PO2 = 40, SO2 = 75%
how does a decrease in PO2 in the upper range (100 down to 60) affect SO2
minimal effect (minor decrease)
how does a decrease in PO2 in the lower range (60 down to 40) affect SO2
significant effect (major decrease)
pulse oximeter
probe that measures O2 saturation
emits 2 wavelengths of light that get absorbed differently by free Hgb and Hgb bound to O2
machine reports SpO2 (pulsatile) - can assume equal to SaO2 (arterial)
P50
the partial pressure of oxygen (PO2) where Hgb is 50% saturated
low P50 = high affinity
high P50 = low affinity
what does it mean if Hgb has a high affinity for O2
- less PO2 required to load
- shifts curve to the LEFT
- caused by decreased PCO2, [H+], temp., and 2,3-BPG
- promotes O2 LOADING in the lungs
what does it mean if Hgb has a low affinity for O2
- more PO2 required to load
- shifts curve to the RIGHT
- caused by increased PCO2, [H+], temp., and 2,3-BPG
- promotes O2 UNLOADING in the tissues
