Transcript Option H. Gaseous Exchange

Option H. Gaseous
Exchange
Mrs. jackie
Define partial pressure
 Diffusion of gas, whether present in air or dissolve in
water depends on differences in a quantity called
partial pressure
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Define as the pressure that one component of a
mixture of gases would exert if it were alone in a
container
Example
 At sea level the atm exerts a total pressure of 760mm
Hg.
 Since the atm s 21% oxygen the partial pressure of
O2 is 0.21*760 or about 160mmhg.
 This is the portion of atmospheric pressure contributed
by O2 hence the term atmospheric pressure.
 The partial pressure of CO2 is 0.23mmHg
Partial Pressure continues
 When water is exposed to air the amount of
gas that dissolves in the water is proportional
to its partial pressure in the air and its
solubility in water.
 An equilibrium is reach when gas molecules
enter and leave the solution at the same rate
 At this point the gas is said to have the same
partial pressure in solution as it does in the
air.
Explain the oxygen dissociation curves of adult and fetal
hemoglobin and myoglobin.
 AS oxygen enters the blood
stream by diffusing from the
alveoli into the capillaries, it
diffuses into red blood cells and
combines with hemoglobin
 When hemoglobin takes the first
molecule of oxygen, it takes the
next one at a faster rate and the
third one is taken even faster.
 This means that the affinity of
hemoglobin to oxygen increases
as it takes more and more
oxygen
 This results in the curve relating
the availability of oxygen to
saturation of hemoglobin with
oxygen to be sigmoidal.
Explain the oxygen dissociation curves of adult and
fetal hemoglobin and myoglobin.
 As shown in the graph
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The saturation of hemoglobin with
oxygen increases as the partial
pressure of oxygen increases.
Hemoglobin become completely
saturated at an oxygen partial
pressure of about 100mmHg
When the partial pressure of
oxygen drops as in the case of the
capillaries near the working
tissues and cells, hemoglobin
releases oxygen to the cells.
Hence hemoglobin associated
with oxygen with oxygen has a
high PO2 as in the case of
capillaries in the alveoli area,
Its dissociates its oxygen when
oxygen has a low P)2 as in the
case of the capillaries in the area
of body tissues and cells.
The case of fetal hemoglobin
 Fetal hemoglobin curve
is shifted to the left due
to its higher affinity to
bind with oxygen.
 The curve is shifted to
the left which means
that fetal hemoglobin
has higher affinity to
oxygen and so it
associates with oxygen
more readily.
The case of myoglobin
 Myoglobin is the
hemoglobin of muscles
 Its has greater affinity to
oxygen and so its binds it
with a high rate
 Is does not dissociate its
oxygen unless the PO2
drops very low.
 It starts to release its
oxygen when the muscle is
exhaust
Describe how carbon dioxide is carried by the blood including the action
of carbonic anhydrase, chloride shift and buffering by plasma proteins.
 Carbon dioxide is carried
in the blood as a
bicarbonate ion.
 A small amount is carried
by the amino groups of the
polypeptides of
hemoglobin.
 CO2 enters a red blood
cell and reacts with water,
resulting in the formation
of carbonic acid.
 This molecules dissociates
into hydrogen carbonate
and hydrogen ions
Describe how carbon dioxide is carried by the blood including the action
of carbonic anhydrase, chloride shift and buffering by plasma proteins.
 Hemoglobin has a high affinity
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to oxygen and so its reacts
with it a high rate, hence
hemoglobin leaves its oxygen
and takes up a hydrogen ion
instead
This frees oxygen molecules,
and so they diffuse out of the
blood cells into the liver cell
which has lower concentration
of O2
Carbonate ions build up and
so they start to diffuse out into
the plasma.
In trade for these ions,
chloride ions enter the red
blood cell.
This is called the chloride shift
to maintain a normal
distribution of ions.
Describe how carbon dioxide is carried by the blood including the action
of carbonic anhydrase, chloride shift and buffering by plasma proteins
 Carbonic anhydrase
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Converts carbon dioxide into bicarbonates and
protons.
Explain the role of the Bohr shift in the
supply of oxygen to respiring tissues
 When oxygen enters the blood cell and
carbon dioxide leaves the blood cell
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CO2 levels increases in the liver cell
More CO2 diffuses into the blood cell and
more O2 is released by hemoglobin
Hence an increase of CO2 causes higher
dissociation of oxygen to the cells
A higher CO2 level causes the oxygen
dissociation curve to shift to the right. This is
called the Bohr shift.
Explain the role of the Bohr shift in the
supply of oxygen to respiring tissues
 Since a higher CO2
results in higher H
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When the acidity of
the blood increase
the graph is shifted
to the right.
This effect helps
tissues get more
oxygen since
shifting to the right
means more
dissociation of
oxygen to the
tissues.
Explain how and why ventilation rate
varies with exercise
 When there are changes in carbon dioxide
concentration there in a decrease in blood pH
 This is detected by chemosensor in the aorta
and carotid arteries
 Chemosensors send impulses to the
breathing center of the brain
 Nerve impulses are then sent to the
diaphragm and the intercostal muscles to
increase the concentration or relaxation rates.