Pulmonary ventilation

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PULMONARY
VENTILATION
BY:
Mrs.Keerthi Samuel
Asst.Professor,
Vijay Marie CON

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TOPICS OF
DISCUSSION
 PULMONARY VENTILATION
 INTERNAL AND EXTERNAL RESPIRATION
 EXCHANGE AND TRANSPORT OF OXYGEN
AND CARBONDIOXIDE
 REPIRATORY CONTROL CENTERS IN BRAIN
 LUNG CAPACITIES AND LUNG VOLUMES

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INTRODUCTION
 RESPIRATION:
The process of exchange of gases
in the body . The following are the main
steps:
 PULMONARY VENTILATION: or
BREATHING is the inhalation and
exhalation of the air and involves the
exchange of air between the
atmosphere and the alveoli of the
lungs.

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RESPIRATION STEPS CONTD…..
1. EXTERNAL (PULMONARY ) RESPIRATION : exchange of gases between the
alveoli and blood in the pulmonary capillaries across the respiratory membrane. In
this process the capillary blood gains oxygen and loss carbon dioxide.
2. INTERNAL (TISSUE ) RESPIRATION: the exchange of gases between blood in
systemic capillaries and tissue cells.in this step the blood looses oxygen and gains
carbon dioxide.
3. CELLULAR RESPIRATION: within the cells the metabolic reaction that consume
o2 and gives off co2 during the production of ATP are termed as CELLULAR
RESPIRATION.

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PULMONARY VENTILATION
 In the pulmonary ventilation air flows between the atmosphere and the
alveoli of the lungs because of the alternating pressure differences
created by the contraction and relaxation of the respiratory muscles.
 Air moves into the lungs when the air pressure inside the lungs is less
than the air pressure in the atmosphere.
 Air moves out of the lungs when the air pressure inside the lungs is
greater than the air pressure in the atmosphere.

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INHALATION
Just before respiration air pressure
in the lungs and atmosphere is the
same ( 760mmhg)
For the air to flow into the lungs the
pressure inside the lungs should be
less than the atmospheric pressure.
This happens when the size of the
size of the lungs increases
following the Boyles law.
BREATHING IN
IS CALLED
INHALATION

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INHALATION-DIAPHRAGM
 The most important muscle of inhalation
is the DIAPHRAGM- a dome shaped
skeletal muscle that forms the floor of
the thoracic cavity.
 It is innervated by fibers of the PHRENIC
NERVES which emerge from the spinal
cord at cervical levels 3,4 and 5 .
 Contraction of diaphragm causes it to
flatten lowering its dome
 This increases the vertical diameter of

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INHALATION
 Flattening of diaphragm
increases the vertical diameter of
 During quiet inhalation the
diaphragm descends about 1cm
reducing 1-3mmhg pressure
thereby inhaling 500ml of air.
 In strenuous breathing the
diaphragm descends 10cms
which produces a pressure
difference of 100mmhg and
inhale 2-3lit of air.

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INHALATION
 Contraction of diaphragm is
responsible for 75% of the air
that enters the lungs during quiet
breathing.
 Advanced pregnancy and
obesity or confining abdominal
clothing can prevent complete
decent of the diaphragm.

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INHALATION-
EXTERNALINTERCOSALS
 The next important muscles of
inspiration.
 When these muscles contract they
elevate the ribs.
 Elevation increases the anteroposterior
diameter and lateral diameters of the
chest cavity.
 Contraction of external intercostals is
responsible for 25% of air that enters
into the lungs during normal quiet
breathing

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During quiet inhalations the pressure between the two membranes that is the
INTRAPLEURAL PRESSURE is always sub atmospheric.
Just before inhalation it is about 4mmhg less than the atmospheric pressure
about 756mmhg at an atmospheric pressure of 760mm hg.
As the diaphragm and external intercostal contract the overall size of the
thoracic cavity increases along with the volume of the pleural cavity.
This causes the intrapleural pressure to decrease to 756mmhg
During the expansion of the thorax both the parietal and visceral pleura are adhered
tightly due to the surface tension between them. The parietal pleura is pulled in all
directions and along with it the visceral pleura and lungs are also pulled

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As the volume of the lung increases this way the
alveolar pressure inside the lungs also drops
from 760 to 758mmhg establishing a pressure
difference.
Since the air flows from an area of higher
pressure to the lower pressure area INHALATION
occurs.
During forceful breathing the ACCESSORY
MUSCLES of respiration (very little contribution)
will help in inhalation
The accessory muscles are –
STERNOCLEIDOMASTOID- elevates the
sternum
SCALENE MUSCLES – elevates the first two
ribs.
PECTORALIS MINOR- elevates third to fifth
ribs

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EXHALATION
 Breathing out is called EXHALATION, and is also due to pressure gradient. In this
case the gradient is in opposite direction.
 The pressure in the lungs is greater than the pressure in the atmosphere.
 During quiet breathing exhalation is a passive process as no muscular
contractions are involved.
 Exhalation results from ELASTIC RECOIL of the chest wall and lungs, which has
natural tendency to spring back after they have been stretched. The two inwardly
directed forces that contributes to elastic recoil are :
 The recoil of elastic fibers that were stretched during inhalation.
 The inward pull of the surface tension due to the film of the alveolar fluid.

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EXHALATION
 Inspiratory muscles relax; diaphragm relaxes, its
dome shape superiorly due to its elasticity.
 Relaxation of external intercoastal causes
depressed ribs.
 These movements decrease vertical, lateral and
anteroposterior diameters of the thoracic cavity,
which decreases the lung volume.
 The alveolar pressure increases to 762mmhg.
And the air flows from the area of higher pressure
in the alveoli to the area of lower pressure into the
atmosphere.

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EXHALATION
 Exhalation becomes active only during forceful
breathing Ex: playing wind instrument or exercise.
 During the these times muscles of exhalation the
abdominals and internal intercostals contract which
increases abdominal and thoracic pressure.
 This contraction moves the inferior ribs downwards and
compresses the viscera forcing the diaphragm
superiorly.

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FACTORS AFFEECTING PULMONARY
VENTILATION
1. SURFACE TENSION:
 alveolar fluid quotes the luminal surface of the alveoli
called surface tension.
 During breathing the surface tension must be overcome to
expand the lungs during each inhalation. Surface tension
is also responsible for lung elastic recoil.
 The SURFACTANT present in the alveolar fluid reduces the
surface tension .deficiency of surfactant in babies is called
Respiratory distress syndrome.

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VENTILATION
2. COMPLIANCE OF LUNGS:
 The effort needed to stretch the lungs is called compliance.
 High compliance- easy expansion of chest wall and lungs and the vice versa( analogy of an
expansion of balloon)
 Compliance of lungs is related to two main factor:
 Surface tension
 Elasticity
 The lungs generally has high compliance but the conditions which decrease the
compliance are:
 Scar lung tissues( TB)
 Edema of the lung tissue (pul.edema)
 Deficiency of surfactant
 Paralysis of muscles ( ICM)

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VENTILATION
3. AIRWAY RESISTANCE:
 The rate of the airflow depends on the pressure difference and resistance.
 The walls of the bronchioles offer some resistance to the normal airflow.
 Larger diameter airways has decreased resistance and vice versa.
 The airway diameter is regulated by degree of contraction and relaxation of the
smooth muscle in the walls of airways which in turn is regulated by the signals
from ANS.

Pulmonary ventilation

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