54: Oxygen Transport Flashcards
Solubility of Oxygen
0.003 ml O2 per 100 ml of plasma
[02] dissolved
PO2 (100) x 0.003
Blood oxygen content is increased by which oxygen carrier molecule?
Hemoglobin
Hemoglobin
tetramer
each monomer has heme group (porphyrin ring with Fe & polypeptide globin)
O2 saturation
25, 50, 75, or 100%
Saturation
fraction of hemoglobin binding sites that are currently occupied of O2 (%)
1 g of hemoglobin
can bind 1.36 ml O2
Oxygen content
1.36 x 15 = 20.4
Saturation Curve
Sigmoid binding curve
Hill coefficient of 2.8, amount of agonist binding to binding site
Why is Hill coefficient of saturation curve not 4?
B/c there’s not complete cooperativity
Cooperativity
once one O2 bound to hemoglobin, it’s easier for next one to bind
binding site affinity increased for agonist
Hemoglobin relaxed state
high affinity for O2
Hemoglobin tense state
low affinity for O2
Percent Saturation equatioin
100 x (PO2)^2.8 divided by (P50)^2.8 + (PO2)^2.8
P50: 50% of binding
P50 of Oxygen
27mm Hg, 50% Hb binding sites are full
low P50: high affinity
high P50: low affinity
Decreased P50
left shift in saturation curve
increased Hb affinity for oxygen
harder to unload oxygen but easier to load oxygen
Increased P50
right shift in saturation curve
decrease Hb affinity for oxygen
easier to unload oxygen
P50 changes
only minor oxygen loading problems occur if P50 changes since alveolar PO2 is 80-100mm Hg
Sigmoid Curve Plateau
Alveolar PO2: loading of O2 good even if alveolar PO2 falls slightly, blood remains well saturated with O2
Sigmoid Curve Steep Region
HbO2 at tissues experience drop in PO2, small change in PO2
leads to a large unloading of O2 from Hb
Anemia
100% saturation, all binding sites are full
there are less binding sites in total
02 content falls but saturation not affected
Anemic patient
has 1/2 the Hb and carries 0.5 times the O2
Polycythemia
increase conc of RBC
more Hb per 100 ml of blood
increased oxygen carrying capacity of blood
no change in affinity just more binding sites
opposite of anemia
Factors Affecting Hb affinity for O2
ph PO2 CO PCO2 temperature 2,3 DPG
Working muscle
heats up, produces CO2, acidic
temp >
ph <
CO2 >
2,3 DPG >
right shift and P50 >
lower affinity for O2
easy unloading
pH Bohr effect
PCO > pH < rightward shift low affinity easy unloading
2,3-DPG
synthesis in RBC enhanced by hypoxia, exercise, high altitudes
holds Hb in tense state, low affinity, high P50
low O2 affinity, helps unload O2 to tissues
feature of chronic hypoxia (COPD, anemia, emphysema)
Venous Blood
low pH high PCO2 P50 increased rightward shift low O2 affinity
Carbon Monoxide
high affinity for Hb
compete with O2 even at low CO concs.
P50 reduced, O2 has greater affinity for O2
harder for Hb to unload the O2 to tissues
reduces carrying capacity of Hb for O2 by binding to O2 sites
driven off Hb by breathing 100% O2
Cooperativity
One O2 site taken up by CO, P50 decreased, O2 unloading reduced
