Question
In which part of the human body is the partial pressure of carbon dioxide greatest?
Solution
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The partial pressure of carbon dioxide (CO2) is a measure of the concentration of CO2 gas in a mixture of gases. In the context of the human body, the partial pressure of CO2 is an important physiological parameter because it reflects the level of CO2 in the blood and tissues, which is a byproduct of cellular metabolism.
The partial pressure of carbon dioxide (CO2) is a measure of the concentration of CO2 gas in a mixture of gases. In the context of the human body, the partial pressure of CO2 is an important physiological parameter because it reflects the level of CO2 in the blood and tissues, which is a byproduct of cellular metabolism.
The partial pressure of CO2 is highest in the venous blood returning to the heart from the body's tissues. This is because as blood circulates through the body, cells use oxygen (O2) for metabolism and produce CO2 as a waste product. The CO2 diffuses from the cells into the blood, where it is carried back to the lungs to be exhaled.
To provide a more detailed explanation, let's consider the journey of blood through the body:
1. Oxygenated blood leaves the left side of the heart and is distributed to the body through the systemic arteries.
2. As the blood passes through the capillaries in the tissues, O2 diffuses from the blood into the cells, while CO2 diffuses from the cells into the blood.
3. The now deoxygenated blood, rich in CO2, collects in the systemic veins and returns to the right side of the heart.
4. The venous blood is then pumped to the lungs, where CO2 is exchanged for O2 across the alveolar-capillary membrane.
5. The blood, now oxygenated and with a lower CO2 concentration, returns to the left side of the heart to be pumped out to the body again.
The highest partial pressure of CO2 is found in the systemic venous blood just before it enters the lungs. This is because it has collected the most CO2 from the tissues. The specific locations where the partial pressure of CO2 is greatest are the venae cavae (the large veins that return deoxygenated blood to the heart) and the right atrium of the heart.
In terms of numerical values, the partial pressure of CO2 in venous blood (PvCO2) is typically around 45 mmHg, whereas in arterial blood (PaCO2), it is lower, usually around 40 mmHg, due to the exchange of gases that occurs in the lungs.
In summary, the partial pressure of carbon dioxide is greatest in the systemic venous blood, specifically in the venae cavae and the right atrium of the heart, where the blood is returning from the body's tissues loaded with CO2.
The partial pressure of CO2 is highest in the venous blood returning to the heart from the body's tissues. This is because as blood circulates through the body, cells use oxygen (O2) for metabolism and produce CO2 as a waste product. The CO2 diffuses from the cells into the blood, where it is carried back to the lungs to be exhaled.
To provide a more detailed explanation, let's consider the journey of blood through the body:
1. Oxygenated blood leaves the left side of the heart and is distributed to the body through the systemic arteries.
2. As the blood passes through the capillaries in the tissues, O2 diffuses from the blood into the cells, while CO2 diffuses from the cells into the blood.
3. The now deoxygenated blood, rich in CO2, collects in the systemic veins and returns to the right side of the heart.
4. The venous blood is then pumped to the lungs, where CO2 is exchanged for O2 across the alveolar-capillary membrane.
5. The blood, now oxygenated and with a lower CO2 concentration, returns to the left side of the heart to be pumped out to the body again.
The highest partial pressure of CO2 is found in the systemic venous blood just before it enters the lungs. This is because it has collected the most CO2 from the tissues. The specific locations where the partial pressure of CO2 is greatest are the venae cavae (the large veins that return deoxygenated blood to the heart) and the right atrium of the heart.
In terms of numerical values, the partial pressure of CO2 in venous blood (PvCO2) is typically around 45 mmHg, whereas in arterial blood (PaCO2), it is lower, usually around 40 mmHg, due to the exchange of gases that occurs in the lungs.
In summary, the partial pressure of carbon dioxide is greatest in the systemic venous blood, specifically in the venae cavae and the right atrium of the heart, where the blood is returning from the body's tissues loaded with CO2.
Partial Pressures and Movement of Oxygen and Carbon Dioxide
The importance of partial pressure in movement of oxygen and carbon dioxide
Lung Diseases and Gas Partial Pressures
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So now that we've looked at partial pressures
in gas pressure and we understand that better,
let's see how that fits in with the respiration.
That is again, the movements of oxygen
from the lung and the alveolus into the bloodstream,
and the movement of carbon dioxide from the bloodstream into the lungs.
The partial oxygen pressure in the lungs, remember,
we figured out how to calculate it,
is going to be roughly 100 millimeters of mercury.
Whereas the partial pressure in
the incoming bloodstream is going to be about 40 millimeters of mercury,
so the oxygen will diffuse from the lung into the bloodstream.
On the other hand, if we look at the carbon dioxide,
the carbon dioxide is at about 46 millimeters of mercury,
partial pressure dissolved in the blood,
whereas in the air,
it's only about 40 millimeters of mercury.
Therefore, it will diffuse from where the pressure is higher,
that is in the blood,
and into the lungs.
When an air mixture reaches the lung,
it gets first humidified.
That's going to change the partial pressure as well,
and the pressure of the water vapor,
which is 47 millimeters of mercury,
will be included in the calculation of the total pressure, and of course,
in our calculations,
that water pressure is going to have to be subtracted from the atmospheric pressure.
Here you can see that the total pressure will be 713 and not 760 at sea level.
The partial pressure of oxygen in the lungs will be about 150 milliliters of oxygen.
It's actually different than what's shown in this figure because there
is some equilibrium with the blood that comes in at about 150.
That's what you can see up here.
The partial pressure in the lungs is about 150 millimeters of mercury,
and the oxygen and carbon dioxide
in the lungs will flow according to their pressure gradient,
as we said before,
from high to low.
We've got different partial pressures.
We've got partial pressure of the carbon dioxide and of the oxygen.
There is a ratio between these 2.
The ratio of the CO_2 production to
the oxygen consumption in the body is somewhere between 0.7, and 1.
Interestingly, when glucose is the diet of cells,
then this respiratory quotient will be about 1 because it's very efficient.
When we start looking at other sources of energy like fat or protein,
then this quotient goes down to 0.8, and 0.7.
If we're talking about fat or fuel,
fat is bit more efficient than protein when it's burned,
and therefore, this quotient will depend on these things.
In any case, there is this quotient which you will see will be important in
calculating how much oxygen and how much carbon dioxide goes in each direction.
This respiratory quotient, the RQ of a pressure of oxygen,
the RQ is used to calculate the partial pressure of oxygen in the alveoli.
That's the PO_2 within the lung,
and the partial pressure of oxygen in the lungs,
as we said, was about 150.
But the inspired air,
that's the air that goes in,
mixes with residual air which was there and that's going to lower,
of course, the partial pressure of the oxygen in the alveoli,
as we saw in that previous diagram.
The O_2 concentration, the oxygen concentration in lungs,
is lower than the air outside the body, of course.
To calculate this, if we know the RQ,
then the partial pressure of oxygen in the alveoli is going to be the inspired.
That's how much the partial pressure of oxygen that we breathe in,
minus what it is in the alveoli over the RQ.
If you plug in the numbers,
remember the exterior partial pressure was 150 for oxygen,
then what we get is that it's roughly 100 millimeters of mercury in the alveoli,
as we mentioned early.
Therefore, oxygen will flow from the inspired air,
which is a 150 into the bloodstream,
which is going to be lower than that.
This video explains the process of respiration, which is the movement of oxygen from the lungs and alveolus into the bloodstream and the movement of carbon dioxide from the bloodstream into the lungs. It also explains the partial pressures of oxygen and carbon dioxide in the lungs and the blood, and how the partial pressure of oxygen in the alveoli is calculated.
Summary:
This video explains the process of respiration, which is the movement of oxygen and carbon dioxide between the lungs and the bloodstream. It discusses the partial pressures of oxygen and carbon dioxide in the lungs and the blood, and how the partial pressure of oxygen in the alveoli is calculated. The partial pressure of oxygen in the lungs is roughly 100 millimeters of mercury, while the partial pressure of oxygen in the incoming bloodstream is about 40 millimeters of mercury. The partial pressure of carbon dioxide in the blood is about 46 millimeters of mercury, while in the air it is only about 40 millimeters of mercury. The total pressure of the air mixture in the lungs is 713 millimeters of mercury, and the partial pressure of oxygen in the alveoli is roughly 100 millimeters of mercury. The oxygen concentration in the lungs is lower than the air outside the body, and the respiratory quotient (RQ) is used to calculate the partial pressure of oxygen in the alveoli.
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