Lecture 5: Transport Of Oxygen And Carbon Dioxide Flashcards
What is tissue oxygenation?
Process of moving O2 and CO2 in and out of body tissues
Diffusion is too slow for distances > than ___
100 micrometers
What are four types of hypoxia?
- Hypoxic hypoxia
- Stagnant (ischemic) hypoxia
- Anemic hypoxic
- Histotoxic hypoxia
Hypoxic hypoxia
- Inadequate O2 uptake into blood in lungs
- COPD
Stagnant (ischemic) hypoxia
- Inadequate blood flow to an organ
- Arteriosclerosis, PVD
Anemic hypoxia
- Inadequate blood oxygen carrying capacity
- Inactivated hemoglobin
Histotoxic hypoxia
- Interference with mitochondrial respiration
- Cyanide poisoning
Hypoxic hypoxia =
Low PO2 (because blood can’t take it up in the lungs)
Anemic hypoxia =
Low hemoglobin
Ischemic hypoxia =
Low perfusion (to an organ)
Cytotoxic hypoxia =
Cells can’t utilize O2
What is O2 carried by?
Red blood cells (erythrocytes)—hemoglobin (Hb)
What is normal hemoglobin concentration?
150 g/L or 15 g/dL
Hemoglobin carries ___ times more O2 than plasma
65 times more
Plasma has a ___ capacity to carry or transport O2
Low
___ amount of O2 dissolved in solution (plasma)
Small
Hemoglobin is a ___
Oxygen carrier protein
Subunits in hemoglobin
- 2 alpha
- 2 beta
How many heme groups in hemoglobin?
4
Only ___ can bind O2
Fe2+
Molecular weight of hemoglobin is ___
64,000
Each gram of hemoglobin can carry up to ___ ml of O2
1.31 ml of O2, theoretically up to 1.39 ml/gm
Hemoglobin is the ___ form
Unoxygenated
Oxyhemoglobin is when ___ is combined
O2
Very ___ coordination bonds between Fe2+ and O2
Loose—easily reversible
Oxygen is carried in its ___ state, not ___
Molecular (O2) state, not ionic O2-
The oxyhemoglobin curve is ___ shaped
Sigmoid
How many oxygen molecules can bind to one hemoglobin (Hb)?
Up to 4 oxygen molecules
What is oxygen saturation?
The ratio of oxygen bound to hemoglobin compared to the total amount that can be bound
What is oxygen capacity?
Maximal amount of O2 bound to hemoglobin
Sat 100 = PaO2 ___
100+
Sat 95 = PaO2 ___
75
Sat 90 = PaO2 ___
60
Sat 75 = PaO2 ___
40 (mixed venous blood in pulmonary artery)
Sat 60 = PaO2 ___
30
Sat 50 = PaO2 ___
27 (Hb P50 point)
Very rough rule—PaO2 40,50,60 for Sat ___
70, 80, 90
P50 of Hb =
PaO2 27
What are ligands of hemoglobin?
Form covalent bonds to the ferrous iron in hemoglobin
The covalent bonds of ligands have ___ affinity to iron than oxygen
More affinity
Oxygen binds ___ to hemoglobin
Weakly
Two types of ligands of hemoglobin:
- Carbon monoxide
- Nitric oxide
Carbon monoxide has ___ times the affinity of oxygen for hemoglobin
250 times
- Does not dissociate readily
- Requires hours to rid body of CO
Nitric oxide binds to Hb ___ times more strongly than oxygen
200,000 times
Hemoglobin binds ___ to NO
Irreversibly
Nitric oxide is used to treat ___
Pulmonary hypertension
The hemoglobin-oxygen equilibrium curve shows the relationship between ___ and ___
Hemoglobin oxygen concentration and oxygen partial pressure
What is the shape of the hemoglobin-oxygen equilibrium curve?
Sigmoid also shape
P50 is the PO2 when hemoglobin is ___ saturated
50%
P50 of Hb = PO2 of ___
27 mm Hg
How is the hemoglobin-oxygen equilibrium curve affected? (2 ways)
- Shift in position
- Change in shape
What indicates a greater interference with O2 transport—change in shape or curve shift?
Change in shape
Increased O2 affinity = shift to the ___
Left
Examples of increased affinity (7)
- Acute alkalosis
- Decreased PCO2
- Decreased temperature
- Low levels of 2,3 DPG
- Carboxyhemoglobin
- Methemoglobin
- Abnormal hemoglobin
Decreased O2 affinity = shift to the ___
Right
Examples of decreased affinity (5)
- Acute acidosis
- High CO2
- Increased temperature
- High levels of 2,3 DPG
- Abnormal hemoglobin
Shift to the right reduces the affinity for O2 below PO2 ___ mm Hg
70 mm Hg
Shift to the right occurs because of ___ PCO2 and ___ ions
Rising PCO2 and rising H+ ions
What is the Bohr effect?
An increase in H+ decreases Hb’s affinity for O2
A shift to the right enhances the quantity of…
O2 released in systemic capillaries
A shift to the right increases ___ of O2 to ___
Delivery of O2 to tissues
Right shift = Hb has ___ affinity for O2, ___ O2, saturation will be ___ for a given PO2
Hb has less affinity for O2, releases O2, saturation will be less for a given PO2
Left shift = Hb has ___ affinity for O2, ___ O2, saturation will be ___ for a given PO2
Hb has higher affinity for O2, binds O2, saturation will be higher for a given PO2
Increased CO2 = shift to the ___
Right
Increased temperature = shift to the ___
Right
Increased metabolism = shift to the ___
Right
Increase H+ = shift to the ___
Right (Bohr Effect)
Acidosis/lactic acid production = shift to the ___
Right
Increased 2,3 DPG = shift to the ___
Right
-2,3 DPG binds to Hb over O2, thus decreases Hb’s affinity for O2
PRBCs are stored ___
Cold
PRBCs have significantly ___ levels of 2,3 DPG
Diminished
Hb in stored blood would initially show a ___ shift in the Hb-O2 dissociation curve
Left shift
What is myoglobin?
Single chained heme pigment found in skeletal muscle
Myoglobin has an ___ affinity for O2
Increased—binds O2 at a lower PO2
Myoglobin stores O2 temporarily in ___
Muscle
What does CaO2 stand for?
O2 content in blood
What does CaO2 measure?
The sum of O2 carried on Hb AND dissolved in plasma
How to calculate CaO2:
CaO2 = (SO2 x [Hb] x 1.31) + (PO2 x 0.003)
CaO2 =
O2 content in blood (ml/dL)
SO2 =
Hb saturation (can use SPO2–pulse ox. Or SaO2–saturation from blood gas (ABG), as a %)
[Hb] =
Hb concentration in gm/dL
1.31 =
O2 binding to Hb (ml/gm)
PO2 =
Arterial blood’s partial pressure of O2
What does DO2 stand for?
Oxygen delivery
How do you calculate DO2?
DO2 = CaO2 x CO (cardiac output)
What can alter the equilibrium curve?
Any factors that reduce Hb’s ability to transport O2
What are two things that can reduce Hb’s ability to transport O2?
- CO
- Anemia
CO ___ the available Hb able to transport O2
Reduces
Anemia
- Decrease in hemoglobin
- Decreases O2 content in blood
Tissue PCO2 is ___ mm Hg
50 mm Hg
Carbonic acid is converted to ___ to be exhaled in the lungs
CO2
CO2 production averages ___ ml/min in resting adult
200 ml/min
During exercise, CO2 production may increase ___
Six-fold
___ amount of CO2 remains in blood and is required in maintenance of the ___
High amount, maintenance in hydrogen ion concentration
Carbon dioxide is transported by blood in three forms:
- Dissolved directly in blood
- Bicarbonate ion (HCO3-) and carbonic acid (H2CO3)
- Bound to hemoglobin and plasma proteins
Most CO2 is ___ for transport
Dissolved directly in the blood
How is the HbCO2 curve different than the HbO2 curve? (2)
- Relationship is linear
- Venous blood transports more CO2 than arterial blood
CO2 equilibrium is affected by ___
O2 saturation of Hb
Ability to bind with CO2 is increased in ___ Hb
Deoxygenated Hb
Deoxygenated Hb is a ___ than oxygenated Hb
Weaker acid
Haldane effect = upon binding O2, Hb releases ___ and ___, which in turn is converted into ___
Releases CO2 and H+, converted into CO2
A-a PCO2 levels are not as affected by ___
V/Q mismatch
Why are A-a PCO2 levels not as affected by V/Q mismatch?
Because the diffusing capacity of CO2 is 20x’s greater than that of O2
