Blood gas - exam 3 Flashcards
What is normal Hb for our class
15g/dL
How much O2 can be bound per gram Hb
1.34mL O2/ gram Hb
Using normal values, what is the O2 carrying capacity of Hb
20.1mL O2/100mL blood
Oxygen content of blood includes O2 that is ______ and ______
dissolved and bound
oxygen content = 20.1 (bound) + 0.3 (dissolved) = 20.4 mL O2
Adult Hb has which sub-units
2 alpha, 2 beta
Fetal Hb has which sub-units
2 alpha, 2 gamma
Fetal Hb has ______ affinity for O2 compared to adult; which allows for what?
higher; allows O2 to unload to fetus more easily
Myoglobin has ______ affinity for O2 compared to Hb
higher affinity than Hb
allows for O2 to unload to muscles more readily
Which hormone is secreted by the kidney to produce RBCs, and what regulates it
Erythropoietin (EPO);
dec hemoglobin → dec oxygen to kidneys → EPO released → more RBCs formed
solubility of O2 =
0.003 mL O2/mmHg/dL of blood
per mL of solution: 0.00003 mL O2/mmHg PO2
solubility of CO2 =
0.06 mL CO2/mmHg/dL of blood
How much CO2 is dissolved vs bound in blood
5% dissolved, 5% carbamino bound, 90% HCO3-
carbon monoxide causes a ______ shift of the oxy-Hb diss. curve
left
carbon monoxide has a _____ affinity for hemoglobin than O2
higher; 200-250x
What 2 things does carbon monoxide do to Hb
- CO decreases carrying capacity of O2
- CO increases affinity for O2 when just 1 CO bound, preventing O2 from unloading
systemic venous Hb is _____ saturated; how does this compare to coronary sinus Hb
systemic venous Hb= 3/4 O2 saturated
coronary sinus Hb= 1/4 O2 saturated
Heart extracts much more O2:
more efficient (reduces coronary perfusion needs), but leaves little room for error (not a lot of extra oxygen to help perfuse injured areas)
A leftward shift of the oxy-Hb dissociation curve means Hb has a _______ affinity for O2
higher; O2 less likely to unload
A rightward shift of the oxy-Hb dissociation curve means Hb has a _____ affinity for O2
lower; O2 more likely to unload
What results in a rightward shift of the oxy-Hb dissociation curve
- inc acidity (dec. pH)
- inc. PaCO2
- inc. temp (hyperthermia)
- inc 2,3 BPG
What results in a leftward shift of the oxy-Hb dissociation curve
- dec acidity (inc. pH)
- dec PaCO2
- dec temp (hypothermia)
- dec 2,3 BPG
What is the normal P50 value for Hb
26.5mmHg
How do the rates of diffusion between CO2 and O2 compare?
CO2 diffuses about 20x greater than O2
What is the primary role of 2,3-BPG in relation to Hb
2,3-BPG binds to deoxygenated hemoglobin and decreases its affinity for oxygen.
2,3-BPG promotes oxygen unloading at the tissue level
What percentage of total CO2 in blood is typically in dissolved form
5%
What is the P50 value of Hb mean
The partial pressure needed to saturate 50% Hb
changes when affinity for O2 changes
How does right shift affect the P50 value
higher P50, need higher PO2 to reach 50%
How does left shift affect the P50 value
lower P50, lower PO2 needed to reach 50%
Normal arterial CO2 content =
48mL CO2/dL (97.5% saturated)
Normal venous CO2 content =
52.5mL CO2/dL (70% saturated)
Which compound is reversibly binding O2 to hemoglobin
Iron (Fe)
What enzyme breaks down carbonic acid (H2CO3) to CO2 and water
Carbonic anhydrase
reaction will occur without it depending on amount of CO2, but carbonic anhydrase speeds it up.
What proportion of CO2 is dissolved vs. HCO3- vs. carbamino bound
- 5% dissolved
- 5% carbamino
- 90% HCO3-
Under normal conditions, what is the normal amount of O2 exchanged in the lungs
5mL O2/dL
(20 - 15 = 5)
Under normal conditions, what is the normal amount of CO2 exchanged in the lungs
4.5mL CO2/dL
(52.5 - 48 = 4.5)
What are the 3 functions of hemoglobin
- bind or release O2
- form carbamino compounds
- buffer protons (H+)
How does the ratio of CO2 forms change in venous blood compared to arterial blood?
Less bicarb form, more carbamino and dissolved forms
The fact that deoxygenated blood has more room to transport CO2 is called the _______ effect
Haldane - depends on oxyhemoglobin saturation levels
How is bicarb transported in/out of RBCs? Which direction in which tissues?
Bicarb-chloride exchanger
- peripheral tissues: bicarb out
- lung tissue: bicarb in
The most notable buffer of protons in a RBC is ________
Hb - deoxygenated
Deoxygenated Hb is a ______ acid, while oxyhemoglobin is a ______ acid
weak - wants to accept protons (good buffer)
strong - wants to get rid of protons
Describe which direction the bicarb buffer equation goes in the RBCs of peripheral tissue
H2O + CO2 → H2CO3 → bicarb + H+
Describe which direction the bicarb buffer equation goes in the RBCs of lung tissue
bicarb + H+ → H2CO3 → H2O + CO2
How long does it take for gas exchange to happen in pulmonary capillaries?
0.25 sec
How long does blood stay in a healthy alveolus at rest?
0.75 sec
At max CO, how long does blood stay in pulmonary capillaries?
0.25 sec
Compared to oxygen, nitrous is _____ soluble, and therefore spends ____ time in the pulmonary capillaries
less, less
CO can be used as a diagnostic tool to test what? Why?
Diffusing capacity bc it has a similar diffusability to oxygen
A __________ gas has equilibration between blood moving through the capillary and alveolar air. What is an example?
perfusion-limited; PO2
A __________ gas does not have equilibration between blood moving through the capillary and alveolar air. What is an example?
diffusion-limited - issue with diffusion, CO
Fick’s law
diffusion of gas
Vgas = (ADΔP)/T
speed of diffusion = (surface areadiffusivitypressure difference)/thickness
Gas diffusivity depends on what two factors?
solubility and sqrt(molecular weight)
Compare the diffusivity of CO2 and O2
- CO2 larger but more soluble than O2
- solubility of CO2 24x > O2
- diffusivity of CO2 20x > O2
(0.85 is MW ratio of O2/CO2; inverse is 1.17 = diffusion rate)
