Oxygen Transport in the blood

2. Oxygen Transport in the blood • Not very soluble in fluids • Can be carried two ways • Physical solution, dissolved in the fluid portion of the blood • In combination with hemoglobin, an iron-protein molecule within RBC

3. @PO2 of 100, 0.3 ml of gaseous oxygen dissolves in 100 ml of plasma, 3 ml/liter

4. @Q of 5 l/min, 15 ml of oxygen carried through body/minute • This would sustain life for about 4 sec • Random movement of dissolved oxygen establishes the PO2 of the blood and tissue fluids • This pressure of dissolved oxygen establishes the PO2 of the blood and tissue fluids • This pressure of dissolved oxygen is important in the regulation of breathing • It also determines the loading and subsequent release of oxygen from hemoglobin in the lungs and tissues (respectively)

5. Oxygen combined with hemoglobin • Increases oxygen carrying capacity 65-70 times • For each liter of blood, 19.7 ml of oxygen are captured (temporarily) by hemoglobin • Each of the four iron atoms in the hemoglobin molecule can loosely bind one molecule of oxygen • Hb4 + 4O2↔ Hb4O8

6. Requires no enzyme • Occurs without a change in the valance of Fe++ (as would be found in oxidation) • The oxygenation of hemoglobin to oxyhemoglobin depends entirely on the PO2 in the solution

7. Oxygen-carrying capacity of Hemoglobin • Males have 15-16 g of Hb/100 ml of blood • Females have 5-10% less, about 14 g/100 ml • Gender difference may account for some lower values in maximal aerobic capacity even after differences in body fat and size are accounted for • Each gram of Hb can combine loosely with 1.34 ml of oxygen • If Hb content of blood is known, the oxygen carrying capacity can be calculated: • Blood’s capacity = Hb X O2 capacity of Hb

8. 20 ml/O2/100 ml = 15 X 1.34 O2/g • Usually ~20 ml of oxygen is carried with Hb in each 100 ml of blood when Hb is fully saturated • If there are significant decreases in Fe in the RBC, decreases in the oxygen-carrying capacity of the blood, decrease the ability to sustain mild aerobic capacity (anemia)

9. PO2 in the lung • Hemoglobin is about 98% saturated with O2 at alveolar PO2 of 100 mm Hg • Therefore, each 100 ml of blood leaving the alveolus has about 19.7 ml of O2 carried by hemoglobin • Remember, 0.3 ml of oxygen is dissolved in the plasma component of the blood • This plasma PO2 regulates the loading and unloading of Hb

10. O2 dissociation curve (Oxyhemoglobin dissociation curve) • Saturation of Hb changes little until the pressure of oxygen falls to about 60 mm Hg • This flat, upper portion of the oxyhemoglobin dissociation curve provides a margin of safety • @~75 mm Hg (altitude or lung disease) saturation is lowered by ~ 6% • If PO2 is lowered to 60 mm Hg, hemoglobin is still 90% saturated

11. PO2 in the tissues • Differences in oxygen content of arterial and mixed venous blood is the arteriovenous difference, or the (a-v)O2 difference • @ rest (a-v)O2 difference is ~4-5 ml of oxygen/100 ml of blood • Large amounts of oxygen remains bound to the hemoglobin, providing a reserve • This reserve can provide immediate oxygen, if the demand suddenly increases

12. When the cells need O2 (exercise), the tissue PO2 lowers, leading to a rapid release of a large quantity of oxygen • During vigorous exercise, extracellular PO2 decreases to about 15 mm Hg, only 5 ml of O2 remain bound to Hb • (a-v)O2 difference increases to about 15 ml of O2/100 ml blood

13. If tissue PO2 falls to 3 mm Hg during exhaustive exercise, almost all of the oxygen is released from the blood that perfuses the active tissue • Without any increase in local blood flow, amount of O2 released to muscles can increase almost 3X above resting, due to more complete unloading of Hb • A working muscle can extract 100% of O2