Download 01 Physiology of breathyng system

Physiology of breathyng.
General functions of respiratory system
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The respiratory system comprises of the
nose, mouth, throat, larynx, trachea,
bronchi and lungs. The function of the
respiratory system is to facilitate gaseous
exchange to take place in the lungs and
tissue cells of the body.
Oxygen is required by cells in the body to
allow various metabolic reactions to take
place and to produce energy and is
therefore essential to life. The respiratory
system may be defined as the organs and
tissues through which air is passed into
and out of the body to allow the
necessary gaseous exchanges to take
place.
Oral and nasal cavity
Functions of air conductive pathway
Lungs
External and internal respiration
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External respiration is the means by which
oxygen from the air passes into the blood
stream for transportation to the tissue cells and
carbon dioxide is collected and transferred back
to the lungs and expelled from the body.
Internal respiration involves the vital chemical
activities which take place in every living cell
requiring oxygen and glycogen to combine and
release energy, water and carbon dioxide.
The normal rate of inspiration and expiration,
the respiration rate, is about 16 times a minute
in an adult.
Biomechanism of breathing
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Breathing is an active process - requiring the contraction of
skeletal muscles. The primary muscles of respiration include
the external intercostal muscles (located between the ribs)
and the diaphragm (a sheet of muscle located between the
thoracic & abdominal cavities).
The external intercostals plus the diaphragm contract to bring
about inspiration:
Contraction of external intercostal muscles > elevation of ribs
& sternum > increased front- to-back dimension of thoracic
cavity > lowers air pressure in lungs > air moves into lungs
Contraction of diaphragm > diaphragm moves downward >
increases vertical dimension of thoracic cavity > lowers air
pressure in lungs > air moves into lungs:
To exhale:
relaxation of external intercostal muscles & diaphragm >
return of diaphragm, ribs, & sternum to resting position >
restores thoracic cavity to preinspiratory volume > increases
pressure in lungs > air is exhaled
Effect of Rib and Sternum Movement
on Thoracic Volume
Effect of Rib and Diaphragm Movement
on Thoracic Volume
Pressure in lungs
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As the external intercostals & diaphragm
contract, the lungs expand. The expansion of
the lungs causes the pressure in the lungs (and
alveoli) to become slightly negative relative to
atmospheric pressure.
As a result, air moves from an area of higher
pressure (the air) to an area of lower pressure
(our lungs & alveoli).
During expiration, the respiration muscles relax
& lung volume descreases. This causes
pressure in the lungs (and alveoli) to become
slight positive relative to atmospheric pressure.
As a result, air leaves the lungs.
Surface tension in lungs
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The walls of alveoli are coated with a thin film of water &
this creates a potential problem. Water molecules,
including those on the alveolar walls, are more attracted
to each other than to air, and this attraction creates a
force called surface tension. This surface tension
increases as water molecules come closer together,
which is what happens when we exhale & our alveoli
become smaller (like air leaving a balloon). Potentially,
surface tension could cause alveoli to collapse and, in
addition, would make it more difficult to 're-expand' the
alveoli (when you inhaled). Both of these would
represent serious problems: if alveoli collapsed they'd
contain no air & no oxygen to diffuse into the blood &, if
're-expansion' was more difficult, inhalation would be
very, very difficult if not impossible. Fortunately, our
alveoli do not collapse & inhalation is relatively easy
because the lungs produce a substance called surfactant
that reduces surface tension.
Pressure in the lungs and intrapleural
pressure
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Intrapleural pressure is always
lower than the alveolar one:
First: chest is a sealed container.
Second, the lungs are
characterized by elastic tension,
which is due to these factors:
1. presence of ellastic fibers,
which make 1 / 3 of elastic
tention;
2. surface tension of the liquid
layer on the inner surface of
alveoli, which makes 2 / 3 of the
elastic tension of the lungs.
Thirdly, “negative” pressure in
the pleural cavity is maintained
by the large absorbtion capacity
of pleural leaves.
Spirometer,
Lung Volumes,
and Lung Capacities
Spirometry
Cardiopulmonary circulation
Proprioreceptive control of breathing.
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Intercostal muscles, and diaphragm in a less extent, contain a
large number of muscle fibers. Proprioreceptors become active
during passive stretching of muscles, isometric contraction and
the isolated contraction of intrafusal muscle bobbins. Receptors
send signals to the corresponding segments
of the spinal cord. Lack of contraction effort of inspiratory or
expiratory muscles increases the impulsation from muscle
bobbins, that increases gamma-motoneuron and then alphamotoneuron activity, in the means of dosing muscular effort.
Receptors of the chest joints send impulses to the cerebral
cortex. These impulses are the only source of information about
the movements of the chest and respiratory volumes.
Arterial chemoreceptors
Location of the
carotid and aortic
bodies. Note that
each carotid body
is quite close to a
carotid sinus, the
major arterial
baroreceptor.
Both right and left
common carotid
bifurcations
contain a carotid
sinus and a carotid
body.
Summary of factors that stimulate ventilation
during exercise