Gas transport: Johnson Flashcards
What governs the movement of air once it is inside the body?
the partial pressures of the gases (moving down its pressure gradient)
What is the normal alveoli PAO2?
100 mmHg, the reservoir of O2 we are using to replenish the deoxygenated blood?????
What are the four steps the pulmonary system had to do in order to ensure das exchange?
- exchange with the environment
- exchange with lung (gas exchnage)
- transport
- exchange with the tissues
What is the partial pressure gradient of oxygen?
60 mmHg
What is the PCO2 in the tissue?
46 mmHg
it is the highest where it is produced; CO2 is a metabolic waste produced by tissues
What is the partial pressure gradient of carbon dioxide?
6 mmHg
What is the diffusion constant for gas in Fick’s law?
takes into account the MW and solubility of the gases
How can supplemental O2 therapy be a treatment for lung disease?
you can increase the partial pressure of O2 in the alveoli allow for a steeper pressure gradient promoting O2 transport
What are the two transport mechanisms of oxygen?
- physically dissolved in plasma
2. chemically bound to hemoglobin in erythrocytes
What is the solubility constant of O2?
low: 0.0031 mL/mmHg of oxygen/dL of blood
this is why hemoglobin is very important
What type of oxygen is detected in the arterial blood gas?
physically dissolved oxygen which is only 2% of total oxygen and supplies 10% of body’s metabolic demand 3mLO2/L blood
thus dissolved O2 CANNOT meet the metabolic needs of the body
What is normal hemoglobin level?
15 g/dL blood
below or above would be anemia or polycythemia respectively
What changes occur to the PaO2 at high altitudes?
- reduction in PaO2 to 60 mmHg as the partial pressure of O2 decreases secondary to decrease in barometric pressure
- thus the inspired oxygen will be much lower at higher altitudes and thus lower O2 saturation in the blood
remember two ways to change PO2 is by changing barometric pressure or inspired air
Describe the changes in PO2 in the systemic venous blood, pulmonary capillaries, systemic arterial blood, and systemic capillaries.
systemic venous blood: 40 mmHg
undergoes gas exchange
pulmonary capillaries: 100 mmHg
mixed with pulmonary shunt blood (which has PO2 of 40 mmHg) to get a
systemic arterial blood with 95 mmHg —> LV–>tissues
oxygen is delivered to the tissues
systemic capillaries 40 mmHg
How does blood admixture occur?
- some blood bypasses the lung and never encounters air space and thus remain deoxygenated
- thus oxygenated blood mixes with oxygenated blood
How does oxygen diffuse from a tissue capillary to the cells?
the pressure gradient determine flow of O2
PO2 in interstitial fluid= 40 mmHg and in tissue cells= 23 mmHg
What is the significant role of hemoglobin (Hb)?
dissolved O2 is only 2% of total O2 and does not meet the demand for O2 in our body
-Hb transports 98% of O2; is the breadwinner as far as delivering O2 to our tissues
What state does Hb need to be in, in order to bind O2?
has to be in the reduced ferrous state to bind O2
Hb has 2 alpha and 2 beta chains to take on O2 for delivery. When an O2 molecule binds to Hb it produces a conformational change in the structural portion of the protein.
When O2 binds to Hb, what happens to the binding affinity of additional O2 molecules?
There is increased affinity. Hb has 4 O2 binding sites. The 4th binding site has the highest affinity.
The total carrying capacity of Hb is 197 mL O2/ L blood satisfying what percentage of O2 consumption at the tissue level?
90%
remember the dissolved O2 only satisfies 10% of the body requirement for O2
The percentage saturation is directly related to the partial pressure of O2. Explain.
Hb is always attached to O2 and this its saturation is an indication of the partial pressure of O2.
PO2 is 40 mmHg in resting cell and 100 mmHg in alveoli.
98% saturation leaving the tissue bed. It means the Hb does not liberate all of the O2 when on the tissue bed. you always have O2 attached to the Hb. That’s why Hb is so important.
What is p50? How many binding sites are filled if Hb is at p50?
p50 represents the partial pressure of a O2 in blood required to achieve 50% saturation
represents the point where the Hb is 50% saturated, meaning 2 binding sites are filled
What does the steep and plateau portion of the Hbg dissociation curve (Hb vs. partial pressure of O2) represent?
Steep portion represents the reducing blood returning from the tissues and the plateau represents the oxygenated blood leaving the lungs.
When is O2 delivery compromised?
PO2 <60 mmHg
During exercise what happens to the amount of O2 bound to Hb?
It decreases as the the body needs to utilize more O2; more O2 delivery is need and Hb is used to carry and deliver that O2 to tissues
What are the physiological factors influencing the oxygen-Hb dissociation curve?
- PCO2
- hydrogen ion concentration
- temperature
- 2,3 DPG
What causes a leftward shift in the O2/ Hb dissociation curve?
increased affinity for O2 causing more O2 to be bound to Hb at a given PO2
- decreased temp
- decreased PCO2
- decreased 2,3-DPG
- increased pH
- decreased p50 (increased affinity)
What causes a rightward shift in the O2/ Hb dissociation curve?
reduced affinity for O2 causing release of O2 that can be used by tissues and cells
- increased temp
- increased PCO2
- increased 2,3-DPG
- decreased pH
- increased p50 (decreased affinity)
What is the Bohr effect?
running up the hill increases metabolic rate:
- temp increases because of increased cellular metabolism
- CO2 increases because muscle is producing lots of CO2 (metabolic waste)
- pH decreases (hydrogen ion concentration increases) because of excess CO2
- 2,3 DPG in RBC is also increased (2,3 DPG favors O2 release from Hb)
The combination of these events shifts O2/Hb dissociation curve to the right facilitating oxygen unloading in the exercising muscle AKA BOHR EFFECT.
How does 2,3 DPG reduce the affinity of O2 to Hb?
2,3 DPG itself has a higher affinity for Hb than O2 and thus it competes with O2 to get to the binding sites on Hb
What happens to 2,3 DPG levels in response to anemia/hypoxia?
it increases in RBCs allowing for more effective O2 delivery
2,3 DPG is produced in large quantities as a byproduct within the RBC via anaerobic glycolysis
increase in 2,3 DPG causes a rightward shift
What are the effects of diffusion and perfusion limitations on gas transport?
Diffusion:
- limited is characterized by incomplete equilibration
- Rate of gas diffusion limits transport away from lungs
- CO
Perfusion
- limited is characterized by complete equilibration
- Rate of gas transport from the lung can only be increase by increased blood flow (i.e. perfusion of pulmonary capillaries)
- O2, N2O
- CO2
How does pulmonary edema affect O2 diffusion?
- interferes with gas exchnage across the alveolar-capillary membrane
- increased interstitial fluid surrounding lung parenchyma impedes diffusion
- increases the diffusion distance limiting the amount of O2 that will reach the pulmonary capillary blood
- results in decreased PaO2
Why is CO poisoning so dangerous?
- CO has a much larger affinity for Hb than O2
- CO has a much larger solubility in lower partial pressures (1-2 mmHg) than O2 (20-60 mmHg) allowing it to bind to Hb more readily
PCO accounts for what type of CO?
CO that is dissolved in plasma NOT bound to Hb; once bound to Hb, it is not part of partial pressure and this goes for O2 as well
The transfer of CO is limited by what?
rate of diffusion NOT the amount of blood available for perfusion
CO is diffusion limited it does not completely equilibrate by the time the blood passes through pulmonary circulation
What is the treatment for CO poisoning?
hyper-barometric chamber (greater than 760 torr) of high concentration of supplemental O2 to displace CO from Hb
Depending on the metabolic activity of tissue causes heterogeneity in the PO2. Explain.
tissues with increased metabolic activity need increased blood flow for increased amount of O2 to be transported to the tissue
If tissue cell exhibit increased utilization of oxygen above normal; PO2 drops. Inverse relationship for PO2 and O2 consumption
What is oxygen saturation?
refers to the amount of O2 bound to Hb relative to the maximal amount of O2 (100% O2 capacity) that can bind Hb
O2 content and O2 carrying capacity are dependent on available Hb in subject’s blood
1 gram Hb binds 1.34 1.39 mL of O2
How does concentration of Hb vary with age?
she will give numbers and explain the scenario
If the PO2 is 100 mmHg in the blood, the Hb saturation is what?
98%
If the PO2 is 60 mmHg in the blood, the Hb saturation is what?
90%
T/F. Subjects with different Hb levels will have different O2 content; but, can have the same hemoglobin saturation.
TRUE!!!
O2 content will be impacted because of the amount of Hb
What are the four types of hypoxia?
- circulatory (stagnant) hypoxia
- hypoxic hypoxia
- histotoxic hypoxia
- anemic hypoxia
What is tissue hypoxia? What is hypoxemia?
insufficient amounts of O2 are available for the metabolic needs of the body
- cyanosis: bluish tinge to the lips and nail bed due to increased levels of deoxyhemoglobin
- Hypoxemia refers to an abnormal PaO2 <80 mm Hg.
What is hypoxic hypoxia?
O2 content of arterial blood is lower and thus cannot deliver sufficient O2 to tissues
PO2 may be low due to either low O2 in alveoli OR diffusion problem limiting O2 going into blood
What is stagnant hypoxia?
- diminished blood flow due to blood clots impacting ability to deliver oxygenated blood
- the heart is the problem as it cannot pump the blood sufficiently due to an obstruction
What is anemic hypoxia?
reduction in the ability to transport O2 either due to fluctuations in Hb amount that is less than the normal value OR CO poisoning
What is histologic hypoxia?
very characteristic of CN poisoning, sodium azide, pesticide rotenone as these chemicals can impact the respiratory system and decreases the ability of the respiratory system to use O2
presence of a poison such as cyanide; inhibition of electron transport chain because of poisoned tissue cells
High altitude, emphysema, pulmonary edema, or fibrosis would be what type of hypoxia?
hypoxic hypoxia
high altitude has low PO2 already
pulmonary edema you have increased diffusion distance due to fluid (harder for O2 to travel in fluid than air)
emphysema is a gas exchange problem as there is deterioration of type 1 alveolar cell membrane
fibrosis: thickening of alveolar membrane impedes the diffusion
If the diffusivity of CO2 is 20 times greater than that of O2 and the solubility of CO2 is much higher….Why is the time to equilibrium the same?
Partial pressure gradients for CO2 is 6 and 60 for O2
solubility of O2 is extremely low and solubility for CO2 is extremely high
they counterbalance one another
If CO2 is high you know something is wrong with the lungs??
Uptake of carbon dioxide by the blood in the tissue capillaries is dependent on what?
??
passive diffusion (has high solubility) and partial pressure gradients (6 mmHg)
How does PCO2 change with metabolism and blood flow?
Decrease blood flow: increased PCO2
Increased metabolism: increased PCO2
How much CO2 and O2 are dissolved in the plasma?
7% for CO2
2% for O2
How much CO2 and O2 are bound to hemoglobin?
23% for CO2
98% for O2
How is CO2 transported in the blood?
- 7% dissolved in plasma
- 23% bound to Hb
- 70% HCO3-
At what level is bicarbonate combined with hydrogen ion to form CO2?
at the level of the lung
Is CO2 diffusion or perfusion limited?
perfusion limited
What is the relationship between the blood CO2 content and partial pressure?
- linear relationship
- there is no plateau
What do the blood CO2 equilibrium curves at different hemoglobin saturation reveal?
- deoxygenated mixed venous blood can transport more CO2
- CO2 curves are essentially straight lines between a PCO2 of 20-80 mmHg , linear relationship
there is higher CO2 content with lowest Hb saturation
What is the Haldane effect?
when O2 binds to Hb it causes Hb to become a stronger acid than CO2 thus displacing CO2 from the blood to the alveolar gas
Method 1: highly acidic Hb has less tendency to bind with CO2
Method 2: increased acidity of Hb causes CO2 to release hydrogen ions
Haldane practically doubles the amount of CO2 released from the blood in the lungs and doubles the amount picked up in the tissues
What is the respiratory exchange ratio? What causes different ratios?
- the rate of CO2 output to O2 uptake
- changes in metabolic condition result in different respiratory exchange ratios
Carbs only R= 1.0
Fats only R= 0.70
What is the normal carrying capacity of Hb? What is the normal O2 saturation?
- Normal O2 carrying capacity of Hb is ~18.76 mL O2/100 mL blood
- Normal SaO2 is ~98%
- 1.34-1.39 of O2 can bind to 1 gram of Hb
- Subjects with different Hb levels will have different O2 content; but, can have the same hemoglobin saturation.
