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8 Cards in this Set

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Calculate the amount of oxygen dissolved in plasma given the PO2.
Dissolved O2 = PO2 x alpha
- alpha = O2 solubility coefficient in plasma = 0.003 ml O2/(100ml blood x mmHg PO2)
Calculate the amount of O2 bound to Hb given PO2.
Bound O2 = O2 capacity x %Hb saturation = (g Hb/100ml blood) x (SO2) x (1.34 ml O2/g Hb)

- SO2 (oxygen saturation) = % of Hb binding sites occupied by O2
-each gram of Hb can bind 1.34 ml O2
Describe the O2 dissociation curve and the importance of its shape.
1) Describes the relationship between PO2 and %Hb saturation or O2 content
2) S-shaped due to cooperative binding
- Hb has ability to bind 4 O2 molecules and binding of one O2 molecule increases affinity for the next O2
- Know three points: 30-50, 60-90 with change in slope at 60mmHg/90% saturation AND PO2 = 40mmHg/75% saturation

3) association part of the curve: flat part with decreasing slope
- relatively flat above PO2 = 60 mmHg (90% saturation)
- almost no change in saturation/content at PO2 greather than or equal 80 mmHg because exponential curve (100mmHg, 97.5% saturated)
- PO2 likely to be present in alveolar capillaries where Hb becomes saturated

4) dissociation part of the curve: steep part with increasing slope due to cooperative binding
- small change in PO2 yield large change in saturation/content
- PO2 found in tissues and facilities transfer of O2 from Hb to mitochondria
Define P50 of normal blood and its significance
PO2 at which 50% of Hb binding sites are saturated with normal O2 (normal P50 = 27 mmHg)

- decreased P50 (left shift curve) = increased binding affinity for O2
- increased P50 (right shift curve) = decreased binding affinity for O2

- significance: best description of Hb binding characteristics or conditions.
Explain the difference between O2 content, capacity, and partial pressure.
1) O2 content takes into account dissolved and bound O2, whereas O2 capacity refers to only O2 bound Hb and partial pressure only to dissolved O2.
Explain what a pulse oximeter reads
Noninvasively measures O2 saturation or SpO2 (fraction of total O2 binding sites occupied as a percentage) by assessing the absorption of red and infrared light transmitted through the tissues.
- calculation based on fact that saturated and desaturated Hb absorb selected light frequences differently
- calculation assumes only arterial blood is pulsatile; non-pulsatile blood is capillary or venous
Know how PCO2, pH, temperature, and` 2,3-DPG affect the affinity of Hb for O2, CO2
1) PCO2: increased CO2 = decreased O2 affinity, which shifts curve right (Bohr Effect); decreased CO2 = increased O2 affinity, left shift

2) pH: low pH (high H+) = low O2 affinity, right shift; high pH (low H+) = increased O2 affinity, left shift
- effects of pH responsible for majority of Bohr effect because change in CO2 affects [H+]

3) temperature: increase temperature = decreased O2 affinity, right shift and vice versa

4) 2,3-DPG: increase [2,3-DPG] = decreased O2 affinity, right shift and vice versa
- compound within RBCs
- hypoxemia (ie altitude) stimulates production
- storage of banked blood depletes 2,3-DPG, so after transfusion, so after transfusion, Hb dissociation decreases for a few days until RBCs regain normal levels.
Describe how CO affects O2 transport
CO binds to Hb with 200-250x the affinity. Thus, even low PCO levels can have a profound effect.

Shifts Hb curve to the left, so that O2 that does bind dissociates less readily

Pulse oximetry cannot distinguish between HbO2 and HbCO because they both absorb similar wavelengths