D.6: Transport of
respiratory gases
Hemoglobin recap…
Oxygen dissociation curves
These curves show the affinity hemoglobin has for
oxygen.
The degree to which oxygen binds to hemoglobin
depends on the partial pressure of oxygen in the blood
(pO2).
Under normal cell conditions, there is a narrow range of
oxygen partial pressure. When pO2 is low (e.g. muscles
during exercise) O2 dissociates from hemoglobin. At high
pO2 (e.g. in the lungs), the hemoglobin becomes
saturated with O2.
http://highered.mheducation.com/sites/0072
507470/student_view0/chapter23/animation
__changes_in_the_partial_pressures_of_oxyg
en_and_carbon_dioxide.html
You do not need to know the pressure changes, but this animation may
help your understanding of why O2/CO2 move in/out of the blood.
CO2 in the blood
Form of transport
Arterial
Venous mmol-1 blood
mmol-1 blood Rest
Exercise
Dissolved CO2
0.68
0.78
1.32
Bicarbonate ion
13.52
14.51
14.66
CO2 bound to
protein
0.3
0.3
0.24
Total CO2 in plasma 14.50
15.59
16.22
pH of blood
7.37
7.14
7.4
Use the data in the table to answer these
questions:
1. Calculate the % of CO2 found as bicarbonate
ions in the plasma of venous blood at rest.
2. Compare the changes in total CO2 in the three
forms between venous blood at rest and
venous blood during exercise
Hydrogen carbonate ions
Carbon dioxide is converted into Hydrogen carbonate ions.
Advantages: more soluble, less toxic
Occurs within RBC, catalyzed by the enzyme carbonic anhydrase.
The reaction is reversible.
The Bohr shift
Higher metabolic activity results in more CO2 being
released into the blood which in turn lowers the
pH.
This increased acidity changes the shape of the
oxygen saturation curve, the hemoglobin has a
lower affinity for oxygen.
The Bohr shift ensures that respiring tissues have
enough oxygen when their need for oxygen is the
greatest.
https://www.youtube.com/watch?v=XJoYdDpy9A4&ebc=
ANyPxKqmm1mERXEzNvT-k9lQTwmKV20aygEfwzPGhti4fq0zJ2sBXUHudPFFUna--IMfiKKfFvm
Effect of CO2 on ventilation rate
Chemoreceptors in the medulla, the aorta and the carotid artery are able to detect a change in blood carbon dioxide.
High levels of carbon dioxide result in an increase in ventilation to prevent CO2 from building up. Normal range of
blood pH = 7.35 – 7.45
As a result, hyperventilation occurs in response to exercise.
*Hyperventilation: rapid, deep breathing*
There are two sets of nerves from the medulla oblongata to the lungs, intercostal nerves (stimulating the intercostal
muscles of the thorax) and the phrenic nerves stimulating the diaphragm.
Stretch receptors in the walls of the chest and lungs indicate when it is time to exhale.
Fetal V’s Adult hemoglobin
Fetal hemoglobin has a higher affinity for
oxygen at all partial pressures to ensure
that O2 is transferred to the fetus from the
maternal blood across the placenta.
It takes approximately 6 months for fetal
hemoglobin to be replaced by adult
hemoglobin.
Smoking