Jackson 3 Flashcards
Less than——– of the oxygen in the blood is dissolved
2%
Dissolved O2 represents what is available to .
diffuse
Resting O2 consumption is ——-, and the amount of dissolved O2 in the blood is less than 10% of what is needed to support ——-.
~250 ml/min, basal metabolism
Therefore, must rely on O2 bound to hemoglobin to carry
~98% of the total O2 in the blood.
Hemoglobin is a respiratory pigment found in mammalian erythrocytes
predominant protein in erythrocytes; estimates of
250-280 million Hb molecules per cell
Hemoglobin: structure
tetrameric molecule – 4 protein subunits, each with a heme group that includes 1 iron atom that can reversibly bind O2
Oxygen carrying capacity of hemoglobin
each subunit can bind an
O2 or not; maximum per molecule of Hb is 4 O2
Carrying capacity (saturation) is reached with maximum
HbO2
% saturation= % of Hb in HbO2
Total O2 in blood is a function of
PO2 and amount of Hb in blood
Binding of O2 to Hb changes the ——- of the Hb molecule, but not the oxygen molecule.
conformation
Hb exhibits
cooperative binding of O2
3Other substances in the blood can also affect Hb’s affinity for O2. For example, binding of======= Hb binding of O2.
2,3 DPG (see figure at right), reduces
Oxygen-hemoglobin dissociation (association?) curve describes the effect of
PO2 on Hb saturation
Oxygen-hemoglobin dissociation (association?) curve has
2 possible y axis.
O2 content – total
O2 per ml of blood
Two regions of the curve describe O2 binding to Hb as a function of
PO2 or the amount of dissolved O2.
Oxygen-heme dissociation curve; Plateau region –
loading phase
Oxygen-heme dissociation curve: Steep region –
unloading phase
Oxygen-heme dissociation curve: P50 is the PO2 at which
½ of Hb is saturated (green line)
Oxygen-heme dissociation curve: Note that the amount of dissolved O2 (red line) changes very little as
PO2 increases.
PO2 is a measure of dissolved O2 and ——– can diffuse into tissues. It is critical to maintain a pool of dissolved O2 to supply ———–
ONLY dissolved O2
mitochondrial demand.
O2 bound to Hb can not diffuse, but O2 is released from Hb into the dissolved pool when —— falls, as it does when O2 diffuses out of the blood into interstitial fluid.
PO2
Changes in Hb affinity have different consequences in plateau and steep phase of curve
increase Hb affinity for O2—–>
shift curve to left and Hb is saturated at a lower PO2
Changes in Hb affinity have different consequences in plateau and steep phase of curve
decrease Hb affinity for O2 —->
shift curve to right and Hb is less saturated for a given PO2
Hb affinity decreased by factors associated with
metabolic activity – curve shifts right
increased T due to production of
metabolic heat
increased CO2 (Bohr effect) –
CO2 binds to globin part of Hb (allosteric effect)
increased H+ (or decrease pH) – H+ also binds to
globin part of Hb and has an allosteric effect
increased 2,3 diphosphoglycerate (2,3,DPG) – 2,3 DPG is a product of ——- in erythrocytes that enhances ——–
glycolysis,
offloading/dissociation of O2 by allosteric modulation
Remember, exercising muscle is warm, acidic, and produces much
DPG
Hypoxic disorders or disorders affecting O2 content
It is important to consider total oxygen content in the blood when interpreting consequences of a disorder. Normal arterial values:
15 g Hb and 20 ml of O2 /100 ml blood
Anemia does not change
arterial PO2 or Hb saturation (?) but total O2 content is reduced
CO replaces O2 on Hb – competes for binding sites on Hb; forms
carboxyhemoglobin
Hb affinity for CO ——- greater than for O2
200-fold
according to Vander, CO also shifts Hb-O2 dissociation curve to the
left (binding of CO will increase Hb’s affinity for whatever O2 is has).
CO2 transported in 3 forms
dissolved (7%)
bound to Hb (~23%)
as HCO3- (70%)
CO2 is more soluble in plasma than
O2
CO2 binds to globin portion of Hb – forms
carbaminohemoglobin
CO2 has no ——— for O2 binding sites (O2 binds to heme portion)
direct competition
Carbonic anhydrase (CA) is the enzyme that catalyzes the formation of ———. CA is found in ——–. Erythrocytes have a ————-.
carbonic acid. CA
eythrocytes (not plasma);
HCO3- / Cl- transporter that moves HCO3- into plasma as it forms (see figure below).
The CA reaction —– the plasma.
acidifies
Some CO2 converted to —— which is transported into plasma
bicarbonate
Carbonic acid reaction reverses which
maintains CO2 gradient into alveolar air.
H+ binds to ———- on Hb, but affinity depends on —–
histidine residues, PO2
oxyHb affinity for H+
low –
deoxyHb affinity for H+
high –
so in the tissues, Hb picks up H+ and minimizes effect of
HCO3- on pH
then in the lung, Hb releases
H+ to combine with HCO3- and CA reaction runs in reverse
Hb buffers most of the H+ produced by the
CA reaction
Respiratory alkalosis:
Respiratory rate
faster than normal or hyperventilation results in decreases in
[H+] and PCO2
breath-holding is extreme
hypoventilation
Respiratory acidosis
Respiratory rate lower than normal or hypoventilation results in increases in
PCO2 and [H+]
