Here Hemoglobin (Hb) is bound with the O2, it provides sync.
In the cell we use O2 inside the mitochondria for the production ofATP/energy.
There is low O2 in mitochondria.
The O2 moves from the erythrocytes (RBC) and the plasma, then into the interstitial fluid and
then the cells.
O2 has a partial pressure of 100mmHg (MILIMETER MERCURY) when it is dissolved in RBC.
This pressure pushed O2 into the interstitial fluid (fluid between cells and blood), then it enters
We need to have a high concentration of 02 in RBC and plasma as compared to its concentration
inside the tissue/cell.
This is opposite to what happens in lungs. Because in lungs we want to keep a low concentration
of O2 in the capillaries surrounding it, so that, the O2 can diffuse from the lungs into the
But right now, we need to keep the O2 concentration high in the RBC because we need to keep a
driving pressure from the lung into the tissue.
We do that by taking the O2, bound to hemoglobin we get rid of it into the dissolved fraction and
that keeps the dissolved fraction high and that’s what gives us our pressure. This allows up to
drive O2 into the cells.
Just like at the lung we wanted to keep low O2 in blood so that it could diffuse into the blood
from the alveoli of the lung (which has high concentration of O2).
Likewise, we need to keep O2 low in cells so we can take O2 from the blood inside the cells.
We don’t have hemoglobin in our cells; it is only in our RBC.
Not just the pressure gradient but the relative amount of this gradient will determine how well or
how much is driven.
We try to keep the gradients as different as possible because the greater the difference, the
greater the pressure is and this is true for all the gases we exchange. Therefore, we want to have
as greater pressure difference as we can. If you have some gases that have different pressure
differences, then the one that has the greater differences will be most efficiently transported.
So we keep O2 level low to allow that large gradient. Slide 93
The important tissues here are skeletal muscle and cardiac muscle. These 2 muscles use the most
We have enough O2 dissolved in our blood to take care of brain function etc.
We need O2 in highly active tissues.
In muscles we have a protein called Myoglobin. Myoglobin is like hemoglobin but “myo” means
Myoglobin does the same thing as Hb, it binds to O2.
Astake is red in color, that red is myoglobin.
Just like hemoglobin gives the RBC its red color, myoglobin gives the muscle its red color as
Myoglobin is present inside the tissue of the muscle and it picks O2 from around the blood
There are some differences between myoglobin and Hb.
1. 1 cell of myoglobin can carry only 1 molecule of O2, whereas, 1 cell of hemoglobin can carry
4 molecules of O2.
2. We talked about how that 4 globin molecule shape and the ability to transport 4 O2 molecules,
gave this O2 hemoglobin dissociation curve a “S” shape.
3. But if you look at myoglobin it doesn’t have that. Really low partial pressure of O2 at the
tissue of muscles have the ability to pick up O2. Haemoglobin won’t be working at the muscle’s
tissue because it would be unloading all its O2 at this low pressure inside the cell, whereas,
myoglobin can hold O2 at very low pressures.
Myoglobin curve doesn’t have a “S” shape because it only carries 1 molecule of O2. It has a very
This allows us to keep the amount of free O2 or dissolved O2 low in the tissue.
O2 comes from hemoglobin, from the blood into cells and it binds to myoglobin.And that gives
us sync within the muscle. Just like we have sync within the blood with Hb.
So, when we need O2 in our muscles we already have it there because of the myoglobin present,
we don’t have to take it from the air, into the blood and down into our muscles. It is already there
in our muscles. We replenish those stores of O2 in myoglobin, as we exercise. In the capillary we have O2 bound Hb. This O2 dissociates from Hb and goes into the extra
cellular fluid (e.c.f) because the partial pressure of O2 is much higher in the capillaries than it is
in the cell. And that pressure drive O2 into the cell. This O2 in the cell is picked up by
Myoglobin (MbO2) and that keeps the partial pressure of O2 low within the cell.
Now you have a sync of O2 in the cell to use when your mitochondria needs it.
If we needed O2, we waited for it to get down from our lungs, to our tissues, then we might be in
trouble and not be able to keep up. So it just gives us a sync and then we replenish that sync. Just
as hemoglobin, myoglobin is present to keep pressure low of O2 and that allows this drive of O2
from the capillary into the tissue to occur.
QUESTION: Hemoglobin carries 4 molecules of O2 and myoglobin carries 1. So how does the
stoichiometry keep up?
Answer:At rest that is pretty much it, you only off load 1 O2 anyway so that you can pick it up.
(Hb releases only 1 O2 into the muscle, so that myoglobin can pick it up.)
When you start to exercise and you are using O2 more, then the amount of O2 in the muscles
will be low, then you will be using more O2 from Hb.Alot of the myoglobin will be free/open
and the O2 won’t even go to Myoglobin, it will go right into the mitochondria but this allows
you to get started.
When doing mild exercise, O2 might bind to myoglobin.
When we utilize O2, we produce CO2.As we manage O2, we also manage CO2.
Alveolar CO2 = PACO2
Arteriolar CO2= PaCO2
Venous CO2= PvCO2.
CO2 in alveoli is 40 mmHg.
CO2 in arteries is 40 mmHg.
CO2 in veins is 46mmHg.
There is only a 6mmHg difference here, not like O2 where we have a 60 mmHg difference.
How do we get CO2 from the tissues out into the lungs to get rid of it.
YOU WONT BE TESTED ON ANY EQUATIONS BUTYOU SHOULD KNOW WAT
PACO2, PaCO2,PvCO2, IS AND KNOW THEIR DIFFERENT PRESSURES. Slide 95
Diffusion drives CO2 movement, driven by concentration and concentration is dependent on
partial pressure (pressure of C02).
Just like how O2 moves from high pressure to low pressure, CO2 is exactly the same.
Like O2 CO2 is transported in multiple ways.
1. 10% of total CO2 is dissolved in plasma, only less of 1% of our O2 was.
O2 has a higher pressure in blood than CO2. CO2 is only 40-46mmHg.At lower driving pressure
you have more CO2 dissolved in blood and this is because CO2 has a much higher solubility
coefficient. (CO2 dissolves in blood faster than O2.)
Pressure=Concentration x solubility coefficient.
We can dissolve more CO2 in blood coz of that solubility coefficient being higher.
2. 30% of CO2 is bound to hemoglobin.
CO2 + Hemoglobin = HbCO2; carbamino Hb.
3. 60% of CO2 is converted to bicarbonate (HCO3-)
TUMS andALKASELTZER are examples of Bicarbonates.
BICARBONATE EQUILIBRIUM REACTION (very important)
CO +2HOH <===> H CO <==2> H 3 HCO 3
It is a reversible reaction.
In this reaction CO2 (gas) and O2 (gas) react together and form CARBONICACID (H2CO3)
and that CARBONIC ACID is converted to Bicarbonate ion (HC03-) and HYDROGEN ion
This is an equilibrium reaction that will always come to some sort of balance.
In order to move this reaction from left to right or right to left, it’s gonna be dependent on the
concentrations of the different variables on each side.
If you increase either variable on one side the reaction gets pushed to the other. The conversion
of carbonic acid to bicarbonate and hydro