Download Gas Exchange at the Muscles

Gas Exchange at the Muscles
Gas Exchange at the Muscles
• Now we have considered how our respiratory
and cardio-vascular system brings air into our
lungs, exchange oxygen and carbon dioxide in
the alveoli, and transport oxygen to the muscles
(and CO2 away from them).
• All that remains is for us to consider the delivery
of oxygen to the muscles from the capillary
blood.
• This gas exchange between the tissue and the
blood in the capillaries is known as – internal
respiration.
The Arterial-venous Oxygen
Difference
• At rest, the oxygen content of arterial blood is
about 20ml of oxygen per 100 ml of blood.
• This value drops to 15 or 16ml of O2 per 100ml
as the blood passes through the capillaries into
the venous system.
• This difference in oxygen content
between arterial and venous blood
is referred to as the arterial-venous
oxygen difference (a-VO2diff).
ARTERIOVENOUS OXYGEN DIFFERENCE
a-vO2 diff
• this expresses the difference between the oxygen carried by
blood in arteries and veins
• and represents the amount of oxygen delivered to working
tissue in the capillary system
venule
a-vO2 diff - AT REST
capillary
15ml O2
per 100ml blood
arteriole
blood flow
20ml O2
per 100ml blood
a-vO2 diff = 5ml
per 100ml blood
a-vO2 diff - DURING INTENSE EXERCISE
venule
capillary
arteriole
5ml O2
per 100ml blood
20ml O2
per 100ml blood
a-vO2 diff = 15ml
per 100ml blood
blood flow
The Arterial-venous Oxygen
Difference
• It reflects the 4-5 ml of oxygen per 100 ml
of blood taken up by the tissues.
• The amount of oxygen taken up is
proportional to its use for oxidative energy
production. Thus as the rate of oxygen
use increases, the a-vO2 diff also
increases.
The Arterial-venous Oxygen
Difference
• E.g. during intense
exercise the a-vO2 diff in
contracting muscles can
increase to 15 to 16 ml
per 100ml of blood.
During such an effort, the
blood unloads more
oxygen to the active
muscles because the
PO2 in the muscles is
drastically lower than
in arterial blood.
Key Point
• The a-vO2 diff increases from a resting
value of about 4 to 5 ml per 100 ml of
blood up to values of 15 to 16 ml per 100
ml of blood during exercise.
• This increase reflects an increase
extraction of oxygen from arterial blood by
active muscle, thus decreasing the oxygen
content of the venous blood.
Factors Influencing Oxygen
Delivery and Uptake.
• The rates of oxygen delivery and uptake depend
on the three major variables.
• The oxygen content of blood.
• The amount of blood flow.
• The local conditions.
• As we begin to exercise, each of these variables
must be adjusted to ensure increased oxygen
delivery to our active muscles.
Factors Influencing Oxygen
Delivery and Uptake.
• We have discussed in class that under
normal circumstances haemoglobin is
98% saturated with oxygen.
• Any reduction in the blood’s normal
oxygen carrying capacity would hinder
oxygen delivery and reduce cellular uptake
of oxygen.
Factors Influencing Oxygen
Delivery and Uptake.
• Exercise causes increased blood flow
through the muscles. As more blood
carries oxygen through the muscles, less
oxygen must be removed from each 100
ml of blood (assuming the demand
remains unchanged).
• Thus increasing blood flow improves
oxygen delivery and uptake.
Factors Influencing Oxygen
Delivery and Uptake.
• Many local changes in the muscle during
exercise affect oxygen delivery and uptake.
• Muscle activity increases muscle acidity
because of lactate production.
• Muscle temperature and carbon dioxide
concentration both increase because of
increased metabolism.
• All of these increase oxygen uploading from
haemoglobin molecule, facilitating oxygen
delivery and uptake by the muscles.
Factors Influencing Oxygen
Delivery and Uptake.
• During maximal exercise,however, when
we push our bodies to the limit, changes in
any of these areas can impair oxygen
delivery and restrict out abilities to meet
oxidative demands.