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