Transcript Pul3.ppt

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