Gas exchange.
Key terms:
• Gas exchange refers to the exchange of gases, namely
oxygen and carbon dioxide and relies on a process
called diffusion.
• Diffusion is the movement of gases from an area of
high pressure to an area of low pressure. The
difference between the high and low pressure is called
the diffusion gradient- the bigger the gradient, the
greater the diffusion and gas exchange that takes place.
• Partial Pressure of a gas is the pressure it exerts within
a mixture of gases. Gas always moves from areas of
high pressure to areas of low pressure.
External Respiration
Inspired air entering the alveoli in the lungs
has a high partial pressure of oxygen and a
low partial pressure of carbon dioxide.
Air in the deoxygenated blood of the
capillaries has a low partial pressure of oxygen
and a high partial pressure of carbon dioxide.
External Respiration
Therefore gas exchange occurs and…
-diffusion of oxygen from the alveoli into the
blood of the capillaries occurs to be
transported to the left atrium of the heart.
-diffusion of carbon dioxide from the capillary
blood into the alveoli of the lungs where it is
expired.
Internal Respiration.
The oxygenated blood is then pumped around the
body until it reaches the capillaries surrounding the
muscles.
The capillary blood has a high partial pressure of oxygen
and a low partial pressure of carbon dioxide.
The muscle cells/tissues have a low partial pressure of
oxygen because it has been used for energy
production, and a high pressure of carbon dioxide
which has been produced as a by product.
Internal Respiration
Therefore, gas exchange occurs and…
-the oxygen passed into the muscle cells is
transferred from haemoglobin in the blood
capillaries to myoglobin, which stores and
transports oxygen to the mitochondria where
it is used for energy production.
-carbon dioxide is transported in the blood as
carbonic acid, carbaminohaemoglobin and
plasma back to the right atrium of the heart.
Make your own flow chart/diagram/table that
represents gas exchange.
Key terms to include:
Gas exchange
Diffusion
Partial Pressure
External Respiration
Internal Respiration
The oxyhaemoglobin dissociation
curve
• 97% of oxygen is carried in the blood by
haemoglobin
• Fully saturated haemoglobin carries 4 oxygen
molecules.
• Haemoglobin is fully saturated when the
partial pressure of oxygen is high, e.g. the
alveolar capillaries at the lungs.
The oxyhaemoglobin dissociation
curve
• At the lungs, the partial pressure of oxygen is high
therefore haemoglobin is fully saturated. At the tissues,
partial pressure of oxygen is low, therefore
haemoglobin gives up some of its oxygen.
• During exercise, deoxygenated blood has an even
higher partial pressure of carbon dioxide and the
oxygenated blood at the lungs has an even higher
partial pressure of oxygen, therefore increasing the
diffusion gradient. This results in greater and quicker
gas exchange therefore greater saturation.
The oxyhaemoglobin dissociation
curve
•
•
•
•
Under certain conditions (exercise) haemoglobin gives up
some of its oxygen more readily and the S-shaped curve
shifts to the right. This is important during exercise when
there is a greater demand for oxygen. These conditions are:
Increase in temperature of the blood/muscle.
Decrease in partial pressure of oxygen in the muscle,
increasing the oxygen diffusion gradient.
Increase in partial pressure of carbon dioxide during
exercise, increasing the carbon dioxide diffusion gradient.
An increase in acidity caused by an increase in carbon
dioxide levels in the blood during exercise, lowering the PH
(Bohr effect).
The oxyhaemoglobin dissociation
curve
All of these factors increase during exercise. The
effect is that the working muscles:
- Generate more heat when working
- Use more oxygen to provide energy, lowering
the PP of oxygen
- Produce more carbon dioxide as a by-product
- Increase lactic acid levels, which increases
blood/muscle acidity, therefore lowering PH.
The oxyhaemoglobin dissociation
curve
Collectively, all 4 of these factors increase the
dissociation of oxygen from haemoglobin,
which increases the supply of oxygen to the
working muscles and therefore delays fatigue
and increases the possible intensity/duration
of performance.
Exam Questions.
• Describe the process of oxygen diffusion at the alveoli during exercise. (3
marks)
• During exercise there is an increased supply of oxygen to the working
muscles. Describe the processes of internal respiration which allow more
oxygen to be diffused into the muscle cell during exercise. (5 marks)