Transcript 33 Transport of gases. Regulation of respiration

Transport of gases.
Regulation of
respiration
Stages of exchange of gases
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} ventilation
} diffusion
1. exchange of gases
between atmospheric air and
intraalveolar air
2. exchange of gases
between intraalveolar air
and blood
3. transport of gases
4. exchange of gases
between blood and tissue
5. internal (tissue)
respiration
} perfusion
Partial pressure is characterized as
a partial quantity of a certain gas
in a mixture of gases. It is equal
to the total pressure times the
fraction of the total amount of gas
it represents.
 Tension of a certain gas means its
quantity dissolved in a liquid.
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Aerohaematic barrier (pulmonary
membrane) includes:
- a thin layer of liquid on the surface of
alveolar cells and surfactant molecules.
-alveolar epithelium;
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- a layer of connective tissue;
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- a layer of endothelial cells of
capillaries;
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- a layer of plasma;
- membrane of erythrocyte.
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Tension of CO2 in venous blood is 46
mm Hg, whereas in alveolar air its 40
mm Hg, that makes CO2 to diffuse
from the blood into the alveoli along
this gradient. CO2 tension in blood
leaving the lungs is 40 mm Hg. CO2
passes through all biologic membranes
with ease, and the pulmonary diffusion
capacity for CO2 is much greater than
the capacity for O2.
Partial pressure and diffusion at the
respiratory membrane.
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The volume of gas that passes
through the aero-hematic barrier
in 1 minute at pressure gradient
of gas on both sides of the barrier
at 1 mm Hg is called diffusive
lung capacity.
Diffusion capacity in human
lungs for oxygen is 25 ml
O2/min*mm Hg.
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Carbon dioxide is 20 times more
soluble in lipids and water than
oxygen. Therefore, despite the smaller
pressure gradient (for CO2 - 6 mm
Hg. and 60 mm Hg for O2), CO2
passes through the pulmonary
membrane faster than O2
Reverse Chloride Shift in Lungs
Insert fig. 16.39
Figure 16.39
Exchange of gases between blood and tissue
The transfer of CO2 from tissues
to blood cells also occurs by
diffusion. The average tension of
CO2 in blood is 40 mm Hg and in
tissues - 50-60 mm Hg.
 CO2 tension in tissues is largely
dependent on the intensity of
oxidative processes (CO2
production).
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Oxygen hemoglobin dissociation
curve, pH 7,40. temperature 380.
RESPIRATORY NEURONS
1. Early inspiratory neurons (impulses grow rapidly and
slowly decreases during inspiration).
2. Late inspiratory neurons (activated at the end of
inhalation).
3. Total inspiratory neurons (slowly activated during
inspiration).
4. Bulbospinal inspiratory neurons (activated
during inspiration and activity gradually decreases
after inspiration)
5. Postinspiratory neurons (impulsation increases
after inhalation).
6. Late expiratory neurons (activated during
exhalation).
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Respiratory neurons of the brain stem have
two types
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- Inhalation (inspirational, I-neurons)
- Exhalation (expiratory, E-neurons).
Exhalation is passive during calm reathing,
so E-neurons are at rest. They become active
if pulmonary ventilation increases.
Functions of the respiratory center in
the respiratory system :
- Motor – contraction of
respiratory muscles.
- Homeostatic - involves
changes in breathing when
disorders of internal O2 and CO2
content occure.
Mechanisms of periodic activity of
the respiratory cycle
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The breathing rate is caused by :
1) coordinated activity of different parts
of the respiratory center;
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2) reception of impulses from receptors;
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3) reception of signals from other parts of
the CNS, including those from the
cerebral cortex.
Receptors that are involved in the
regulation of breathing
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1. Hemoreceptors: a) central;
b) peripheral.
2. Mechanoreceptors of upper and lower
respiratory ways.
3. J-receptors.
4. Irritant receptors.
5. Receptors of pleura.
6. Proprioreceptors of respiratory muscles
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.
Reflexive regulation of breathing
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- Reflexes from the mucosa of the nasal cavity.
Stimulation of irritational receptors of the nasal
cavity mucose (tobacco smoke, dust particles and
gaseous substances, water) cause:
- narrowing of the bronchi, vocal fissure.
- bradycardia,
- decrease in cardiac output,
- narrowing of the vessels of skin and muscles
Respiratory Structures in the Brainstem
Reflexes from the larynx and trachea.
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Receptors are stimulated by dust, caustic
gases, bronchial secret and alien bodies. It
causes a cough reflex, which is expresed in
a quick exhalation on a background of
narrowing of the larynx and contraction of
bronchial smooth muscle, which remains
long after the reflex.
Cough reflex is the main pulmonary reflex
of the vagus nerve
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 gammamotoneuron 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.
Summary of factors that stimulate
ventilation during exercise