1. Transport of gases:

• In the general scheme, this corresponds to the second major step: the cardiovascular step, where the heart ensures the convection of oxygen to muscle capillaries.

We can calculate oxygen consumption:

• CO x (CaO2 - CvO2) = V’O2
• CO= Qc
• Arterial content
• Venous content

2.Forms of oxygen transport:

O2 is transported in two forms:

Dissolved O2: For every mmHg of PO2 = 0.003 mL of dissolved O2 for 100 mL of blood, so:

• Dissolved O2 = PO2 x 0.003 according to Henry's law.
• 1 L of blood at a PO2 of 100 mmHg contains 3 mL of dissolved O2.

O2 combined with hemoglobin:

• (H) Hb + O2 = HbO2 (+H).

Properties of hemoglobin:

• 4 monomers of globins (2 alpha chains + 2 beta chains),
• 1 heme group in the pocket of each chain: 1 porphyrin nucleus and 1 ferrous iron atom
• Allosteric molecule: Binding of the first O2 molecule makes it easier to bind the following ones (the binding rate of the 4th molecule is 400 times faster than that of the first).

The oxygen-carrying capacity of Hemoglobin:

• Is the volume of O2 that can be bound by 1 g of Hb at maximum = 1 g of Hb can combine with 1.34 mL of O2.

The capacity of Hb in O2:

• Is the maximum volume of O2 that can be combined for all of the Hb present.
• For example: for [Hb]=15g/dL: CapO2 = 15 x 1.34 = 20.1 mL of O2/100 mL of blood.
• Cap = capacity

Arterial oxygen saturation (in %):

Concentration (or oxygen content):

• O2 bound to Hb > dissolved O2.

A.Hemoglobin dissociation curve:

The oxygen content and the saturation of hemoglobin depend on the PO2.

• The relationship is not linear.
• Dissolved O2 (right curve) is minimal compared to O2 bound to Hb.

Various levels:

• Oxygenated blood from the lungs: 2 levels of O2 saturation: alveolar and capillary = on the dissociation curve.
• Oxygen taken up by tissues = ascending part of the Hb dissociation curve.

The advantage of the Hb dissociation curve: is that we go from 100 mmHg of PaO2 to 60mmHg (a 40% decrease) without reducing the transport of O2 (oxygen content) by more than 10%.

• There is also the P50 which reflects the affinity of hemoglobin for O2.
• It is defined as the value of PO2 necessary to saturate 50% of the Hb sites. (27mmHg)

Shift of the dissociation curve:

• To the right when PCO2 is elevated: PCO2 > 45mmHg
• To the left when PCO2 decreases: Increases Hb affinity for O2. / Better saturation in case of decreased PO2.
• pH = 7.2 so pH decreases shifting the curve to the right = increase in P50. And vice versa.
• An increase in temperature promotes the release of O2.

The physiological factors that can modify the affinity of normal adult Hb for O2 are:

• pH: a decrease in pH reduces the affinity of Hb for O2 (curve then shifted to the right).
• CO2: its increase reduces Hb affinity for O2.
• Tissue temperature: its increase reduces Hb affinity for O2.
• = Increase in affinity = shift of the curve to the left; decrease in affinity = to the right.

3.CO2 transport:

3 forms of CO2 transport:

Dissolved CO2 =

• Follows Henry's law.
• CO2 is highly diffusible and has a high solubility coefficient (20 times that of O2).
• There is 0.065mL of dissolved CO2 / mmHg of PCO2 / 100 mL of blood, which represents 5% of the total CO2 in venous blood.

Bicarbonates =

• Are the predominant form of transport: 90% of venous CO2.
• The formation of bicarbonates in plasma is minor.
• Bicarbonates are mainly produced in red blood cells.

Carbamino forms (carbamates) =

• Corresponds to the combination of CO2 with terminal amino groups of proteins. (ex: carbamino-hemoglobin = HbCO2).
• They represent 5% of the CO2 transported in venous blood.
• The binding is facilitated by the reduced form of Hemoglobin (Haldane effect).

The dissociation curve of CO2 is different from that of O2:

There is a relationship between CO2 content and CO2 partial pressure that is almost linear in the physiological range.

• With dissolved CO2 gradually increasing with PCO2
• CO2 bound to bicarbonates HCO3-
• CO2 bound to carbaminates.
• When comparing the dissociation curves of O2 and CO2, one can see that one is linear (CO2) while the other is not (O2).