Respiration:-exchange of O2 and CO2 between
atmosphere and body cells is called respiration.
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1)Exchange of O2 and CO2 between alveolar air
and blood.
2)Excretion of volatile substances eg. NH3,keton
bodies essential oils, alcohol, water vapours, etc.
Maintenance of acid –base balance by adjusting
CO2 elimination.
4)Maintenance of temp. balance by losing heat in
expired air.
5)Helps venous return by dec. intra-thoracic
pressure and inc. intra-abdominal pressure during
inspiration.
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Atmospheric pressure – 760 mm Hg,
Intrapleural pressure – 756 mm Hg – pressure
between pleural layers
Intrapulmonary pressure – varies, pressure
inside lungs
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Diameter of airways, esp. bronchioles
Sympathetic & Parasympathetic NS
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Surface tension tends to oppose alveoli
expansion
Pulmonary surfactant reduces surface tension
 Mechanism
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of inspiration:-
inspiration is induced by the contraction of the diaphragm(
main muscle of inspiration), along with some accessory
muscles that expand chest wall. (active process)
Net effect of contracting these muscles is to decrease (make
more negative ) intrapleural pressure.
The expansion of lung causes the gases in the alveoli to
expand , creating a slightly negative alveolar pressure. This
causes air to flow into the lungs.
Other muscles of inspiration are used primarily during
exercise or in diseases that increases airway resistance (e.g.
asthma).
Vertical diameter of chest cavity is inc. by downward
movement of diaphragm.
Antero-posterior diameter of chest cavity is inc .by elevation
of ribs
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Expiration under resting conditions is produced simply by the
relaxation of the muscles of inspiration. (passive process).
The relaxation of the diaphragm and accessory muscles of
inspiration increases (make more positive) intrapleural
pressure.
Lung deflation begins.
Deflation of lung compresses the gases in the alveoli,
creating a slightly positive alveolar pressure .This causes air
to flow out of the lungs.
Muscles of expiration are used during exercise or increased
airway resistance (e.g. asthma).
Vertical diameter of chest cavity is dec. by upward movement
of diaphragm.
Antero-posterior diameter of chest cavity is dec. by
depression of ribs.
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1)Diaphragm (primary muscle of inspiration).
2)Sternocleidomastoid (elevates sternum).
3)Serratus anterior.
4)scaleni( elevates first two ribs).
External intercostals. (moves ribs upward and
outward)
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1)Elastic recoil of lungs( it is not muscle , but
it is the main factor).
2)Rectus abdominus (main muscle).
3)Internal intercostals. (pull ribs downward
and inward).
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1)Tidal volume (TV):- It is volume of air
inspired or expired with each normal
breath.
Value:- 500 ml.
2)Inspiratory Reserve volume (IRV):- It is
extra volume of air that can be inspired
forcefully over and beyond normal tidal
volume.
Value:- 3000 ml
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3)Expiratory Reserve volume (ERV):- It is
extra volume of air that can be expired
forcefully over and beyond normal tidal
volume.
Value:- 1100 ml
Residual volume (RV):- It is volume of air
remaining in lungs after most forceful
expiration. (amount of air that can never be
expelled from lung).
Value:- 1200 ml.
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Combination of two or more pulmonary volumes, is
called pulmonary capacity.
1)Inspiratory Capacity (IC):- It is combination of
tidal volume and inspiratory reserve volume.
Value:- 3500 ml.
2)Functional Residual Capacity (FRC):- It is
combination of expiratory reserve volume and
residual volume OR volume of gas in the lungs at
the end of a passive expiration or with the glottis
open and all respiratory muscles relaxed. This is
also considered to be the natural or equilibrium
point for the respiratory system.
Value:- 2300 ml.
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3)Vital Capacity:- It is combination of
inspiratory reserve volume, tidal volume
and expiratory reserve volume.
Value:- 4600 ml.
4)Total Lung Capacity (TLC):- It is
combination of vital capacity and residual
volume . It is the maximum volume to
which lungs can be expanded with greatest
possible inspiratory efforts.
Value:- 5800 ml.
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A) Nervous control:Respiratory center.
B) Chemical controlChemosensitive area in brain.
Peripheral chemoreceptors ( carotid and
aortic bodies).
Group of neurons located bilaterally in medulla
and pons which control all aspects of
respiration.
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The Respiratory Centers Are Composed of
Three Main Groups of Neurons:1)The Dorsal Respiratory Group.
2)The Pneumotaxic Center.
3)The Ventral Respiratory Group.
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For spontaneous breathing, an intact
medulla must be connected to the diaphragm
(via the phrenic nerve). Thus a complete C1
or C2 lesion will prevent diaphragmatic
breathing but not complete C6 or lower
lesion.
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1)Increasen activity of vasomotor center .
2)Increase body temprature.
3)Increase CO2.
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4)Decrease O2
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How Gases Are Transported
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O2 is transported by the blood either,
◦ Combined with haemoglobin (Hb) in the red
blood cells (>98%) or,
◦ Dissolved in the blood plasma (<2%).
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The resting body requires 250ml of O2 per
minute.
We have four to six billion haemoglobin
containing red blood cells.
Haemoglobin molecules can
transport up to four O2’s
When 4 O2’s are bound to
haemoglobin, it is 100%
saturated, with fewer O2’s it is
partially saturated.
Co-operative binding:
haemoglobin’s affinity
for O2 increases as its
saturation increases.
Oxygen binding occurs in
response to the high PO2 in
the lungs
 Haemoglobin
saturation is
the amount of oxygen
bound by each molecule of
haemoglobin
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Each molecule of haemoglobin can carry
four molecules of O2.
When oxygen binds to haemoglobin, it
forms OXYHAEMOGLOBIN;
Haemoglobin that is not bound to oxygen is
referred to as DEOXYHAEMOGLOBIN.
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The binding of O2 to haemoglobin depends
on the PO2 in the blood and the
bonding strength, or affinity,
between haemoglobin and
oxygen.
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The graph on the following page shows an
oxygen dissociation curve, which reveals the
amount of haemoglobin saturation at
different PO2 values.
Reveals
the amount of
haemoglobin
saturation at different
PO2 values.
Haemoglobin saturation is
determined by the partial
pressure of oxygen. When
these values are graphed
they produce the Oxygen
Disassociation Curve
In the lungs the partial
pressure is
approximately 100mm
Hg at this Partial
Pressure haemoglobin
has a high affinity to 02
and is 98% saturated.
In the tissues of other
organs a typical PO2 is
40 mmHg here
haemoglobin has a
lower affinity for O2
and releases some but
not all of its O2 to the
tissues. When
haemoglobin leaves the
tissues it is still 75%
Lungs at sea level:
PO2 of 100mmHg
haemoglobin is
98% SATURATED
When the PO2 in the
lungs declines below
typical sea level
values, haemoglobin
still has a high affinity
for O2 and remains
almost fully saturated.
Lungs at high
elevations: PO2
of 80mmHg,
haemoglobin
95
% saturated
Even though PO2
differs by 20
mmHg there is
almost no
difference in
haemoglobin
saturation.
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Blood acidity…
Blood temperature…
Carbon Dioxide concentration
Respiratory Response to Exercise
BLOOD TEMPERATURE
 increased blood temperature
 reduces haemoglobin affinity for O2
 hence more O2 is delivered to
warmed-up tissue
BLOOD Ph
• lowering of blood pH (making blood
more acidic)
• caused by presence of H+ ions from lactic
acid or carbonic acid
• reduces affinity of Hb for O2
• and more O2 is delivered to acidic sites
which are working harder
CARBON DIOXIDE CONCENTRATION
• the higher CO2 concentration in tissue
• the less the affinity of Hb for O2
• so the harder the tissue is working, the
more O2 is released
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Carbon dioxide also relies on the blood for
transportation. Once carbon dioxide is
released from the cells, it is carried in the
blood primarily in three ways…
Dissolved in plasma,
As bicarbonate ions resulting from the
dissociation of carbonic acid,
Bound to haemoglobin.
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Part of the carbon dioxide released from the
tissues is dissolved in plasma. But only a
small amount, typically just 7 – 10%, is
transported this way.
This dissolved carbon dioxide comes out of
solution where the PCO2 is low, such as in
the lungs.
There it diffuses out of the capillaries into
the alveoli to be exhaled.