Gas Transport and Delivery

oxygen

carbon dioxide

methods of transportation

bound to Fe in heme group on hemoglobin (inside RBCs) (98.5%)

plasma (1.5%)

methods of transportation

bound to amino group of Hb inside RBCs (23%)

dissolved in plasma (7%)

dissolved in plasma as HCO3- (70%)

hemoglobin and oxygen association

oxy-hemoglobin = Hb and O2 combination

deoxy-hemoglobin = Hb that has no O2 bound

hb is composed of 4 polypeptide chains = 2 alpha units and 2 beta units

fully saturated Hb = all four heme groups carry an O2 molecule

the loading and unloading of O2 from Hb is faciliated by a conformational change of Hb

partially saturated = 1-3 of the heme groups carry an O2 molecule

HYPOXEMIA = Hb-O2 saturation below 90%

fetal hemoglobin

structure of Hb F differes from adult Hb: it has 2 gamma chains instead of 2 beta chains (this gives it higher affinity for O2 given the same PO2)

it is destroyed in the liver after birth

Oxygen-Hb saturation curve

P50 (26.8) = partial pressure of O2 at which Hb is 50% saturated (2/4) heme molecules are bound by O2

an increase in P50 = lower affinity

a decrease in P50 = increased affinity

Bohr Effect

when pH drops (acidosis, increased H+) P50 increases and Hb affinity for O2 drops (this means O2 more readily diffuses into tissue)

when pH is increased P50 decreases and Hb affinity for O2 increases (O2 diffuses less readily than at normal pH)

effect of temperature: when temp. rises more O2 dissociates, decreased affinity = higher P50

CO2 is converted into H2CO3 (in the RBCs) using carbonic anhydrase as a catalyst

H2CO3 then dissociates into H+ and HCO3-

HCO3- moves out of the RBC and into the plasma in exchange for 1 Cl- which enters the RBC

When the HCO3- gets to the pulmonary capillaries it enters the RBCs where it binds with H+ to make H2CO3, then it split by carbonic anhydrase into water and CO2, then the CO2 diffuses into the alveoli