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