Breathing and Exchange of Gases -2 Flashcards
what is the exchange of gases and what are the factors affecting it?
Alveoli are the primary sites of exchange of gases. Exchange of gases also
occur between blood and tissues. O2
and CO2
are exchanged in these
sites by simple diffusion mainly based on pressure/concentration
gradient. Solubility of the gases as well as the thickness of the membranes
involved in diffusion are also some important factors that can affect the
rate of diffusion.
what is partial pressure
Pressure contributed by an individual gas in a mixture of gases is
called partial pressure and is represented as pO2
for oxygen and pCO2
for
carbon dioxide.
During inhalation, the oxygen moves from a region of high partial pressure to a region of low partial pressure. During exhalation, the carbon dioxide moves from a region of high partial pressure to a rgion of low partial pressure.
how does solubility important for exchange of gases
As the solubility of CO2
is
20-25 times higher than that of O2
, the
amount of CO2
that can diffuse through the
diffusion membrane per unit difference in
partial pressure is much higher compared
to that of O2
.
how does thickness ofmembrane affect exchange of gases
The diffusion membrane is
made up of three major layers (Figure 17.4)
namely, the thin squamous epithelium of
alveoli, the endothelium of alveolar capillaries
and the basement substance in between
them. However, its total thickness is much
less than a millimetre. Therefore, all the
factors in our body are favourable for
diffusion of O2
from alveoli to tissues and that
of CO2
from tissues to alveoli.
how are the gases transported through the blood
Blood is the medium of transport for O2
and CO2
. About 97 per cent of O2
is
transported by RBCs in the blood. The remaining 3 per cent of O2
is carried
in a dissolved state through the plasma. Nearly 20-25 per cent of CO2
is
transported by RBCs whereas 70 per cent of it is carried as bicarbonate.
About 7 per cent of CO2
is carried in a dissolved state through plasma.
how is oxygen transported
Haemoglobin is a red coloured iron containing pigment present in the
RBCs. O2
can bind with haemoglobin in a reversible manner to form
oxyhaemoglobin. Each haemoglobin molecule can carry a maximum of
four molecules of O2
what does oxygen transport depen upon
Binding of oxygen with haemoglobin is primarily
related to partial pressure of O2
. Partial pressure of CO2
, hydrogen ion
concentration and temperature are the other factors which can interfere
with this binding.
what is oxygen dissociation curve
It is the sigmoid curve which shows us the relationsup between percentage saturation of haemoglobin with oxygen and partial pressure of oxygen.This curve is called the Oxygen
dissociation curve (Figure 17.5) and is highly
useful in studying the effect of factors like
pCO2
, H+
concentration, etc., on binding of O2
with haemoglobin.
explain how oxygen associates and dissociates in the alveoli and tissues
In the alveoli, where there
is high pO2
, low pCO2
, lesser H+
concentration
and lower temperature, the factors are
all favourable for the formation of
oxyhaemoglobin, whereas in the tissues,
where low pO2
, high pCO2
, high H+
concentration and higher temperature exist,
the conditions are favourable for dissociation
of oxygen from the oxyhaemoglobin. This
clearly indicates that O2
gets bound to
haemoglobin in the lung surface and gets
dissociated at the tissues. Every 100 ml of
oxygenated blood can deliver around 5 ml of
O2
to the tissues under normal physiological
conditions.
how does oxygen bind wit haemoglobin
Haemoglobin protein consists of the quartnernary structure of protein which in turn consits of 2 alpha and 2 bete polypeptide chaisn. Each chain consistsof a haem complex which has one atom of Fe each. There for each molecule of haemoglobin can bind with 4 o2 molecules. the oxyhyaemoglobin is formed due to copperative binding of oxygen molecules to haem complexes.
explain how co2 is tranported in the form of carb amino haemglobin
CO2
is carried by haemoglobin as carbamino-haemoglobin (about
20-25 per cent). This binding is related to the partial pressure of CO2
.
pO2 is a major factor which could affect this binding. When pCO2
is high and pO2 is low as in the tissues, more binding of carbon dioxide occurs whereas, when the pCO2 is low and pO2 is high as in the alveoli, dissociation of CO2
from carbamino-haemoglobin takes place, i.e., CO2
which is bound
to haemoglobin from the tissues is delivered at the alveoli.
who helps in carbon dixoide dissocation and association
RBCs contain
a very high concentration of the enzyme, carbonic anhydrase and minute
quantities of the same is present in the plasma too. This enzyme facilitates
the following reaction in both directions.
H2O+ CO2<—–carbonic anhydrase—> H2CO3<—-carbonic anhydrase——> HCO3- + H+
how is blood transported in plasma
At the tissue site where partial pressure of CO2
is high due to
catabolism, CO2
diffuses into blood (RBCs and plasma) and forms HCO3
–
and H+,. At the alveolar site where pCO2
is low, the reaction proceeds in
the opposite direction leading to the formation of CO2
and H2O. Thus,
CO2
trapped as bicarbonate at the tissue level and transported to the
alveoli is released out as CO2 (Figure 17.4). Every 100 ml of deoxygenated
blood delivers approximately 4 ml of CO2
to the alveoli.
