Oxygen Dissociation Curve

Ian Gabrielle Cuyno

Terms

Carrier of O2 and CO2 Also functions in acid-base balance as a

buffer Is an allosteric molecule

◦ Its functionality depends on surrounding molecules

Hemoglobin

2,3, Diphosphoglycerate Responsible for tensed or relaxed state of

Hemoglobin

Low 2,3 DPG = more room for O2 (inc. affinity)

High 2,3 DPG = less room for O2 (dec. affinity)

2,3 DPG

The tendency of Hb to hold or release O2◦High Affinity

Tendency to retain O2 Property needed in lungs (O2 absorption)

◦Low Affinity Tendency to release O2 Property needed in peripheral tissues (O2

release)

Affinity

Partial pressure of oxygen Oxygen content in environment of RBC Lungs = High PO2 Tissues = Low PO2

PO2

Percent content of O2 in RBCs PO2 Increase = Increase in % Saturation

Oxygen Saturation

O2 needs to be absorbed in lungs (High Affinity)

O2 needs to be released in tissues (Low Affinity)

Note:

Discussion

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Oxygen Dissociation Curve

PO2

% O

2 S

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P50 = 27 mmHg

The pO2 needed to saturate RBCs to 50% Normal value = 27 mmHg

p50

Indicates changes in O2 affinity of Hb Affected by various factors Seen as shift in p50

Shift in the Curve

Factor Left Right

Temperature Decrease Increase

2,3, DPG Decrease Increase

CO2 Decrease Increase

pH Increase Decrease

Factors which shift the curve

Increased affinity for O2 Less PO2 needed to saturate Hb (greater O2

content) Tendency to retain O2 (not give it to tissues)

Shift to the Left

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Oxygen Dissociation Curve

PO2

% O

2 S

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Respiratory Alkalosis◦ Caused by Hyperventilation

Hypothermia

Conditions causing shift to the Left

Decreased affinity for O2 more PO2 needed to saturate Hb (less O2

content) Tendency to release O2 (give it to tissues)

Shift to the Right

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Oxygen Dissociation Curve

PO2

% O

2 S

atu

rati

on

P50 = 37 mmHg

Respiratory Acidosis◦ Increased CO2◦ Usually coupled with HYPOXEMIA

Hyperthermia◦ Tissues need more O2

Conditions causing shift to the Right

Hemoglobin’s function as gas carrier also affects body’s acid-base balance

Note

CO2

Hemoglobin also carries CO2

In the tissues: CO2 + H2O = H2CO3 (Carbonic Acid)

H2CO3 = H+ + HCO3- (Bicarbonate)

◦ Bicarbonate enters RBC membrane to be carried to lungs

CO2

Hb(02)4 + H2O + CO2 = Hb- + H2CO3 + 4O2

In the RBC: Hb- + H2CO3 = HB + HCO3

In the Body

Hb + 4O2 = Hb(02)4 (Oxygenated) + H+

Note: H+ release corrects Alkalosis caused by Hyperventilation

In the RBC H+ + HCO3- = H2O + CO2 (expelled)

In the Lungs