 Pulmonary ventilation: air is moved in and
out of the lungs
 External respiration: gas exchange between
blood and alveoli
 Respiratory gas transport: CV system
transports oxygen and carbon dioxide
between lungs & tissues (discussed in Blood
chapter)
 Internal respiration: gas exchange between
blood & tissue cells
 Definition: Cellular respiration: actual use of
oxygen & production of carbon dioxide in the cells
 (this is why we have to breathe!!)
 Pulmonary ventilation: - Moving air into and
out of the lungs
 Depends on pressure changes
 Breathing
 Inspiration = moving air into the lungs
 Expiration = moving air out of lungs
 Intrapulmonary pressure
 Pressure within the alveoli (lungs)
 Changes with phases of breathing
 Always equalizes itself with atmospheric pressure
 Intrapleural pressure
 Pressure within intrapleural space (between the
pleural membranes )
 Always 4 mmHg less than intrapulmonary pressure
 Any conditions that causes intrapulmonary
pressure to equal intrapleural pressure will
cause the lungs to collapse
 This means they lose the
ability to move air since
there is NO more pressure
difference

term for lung collapse

Air in the intrapleural
space due to trauma –
causes lung collapse
 Question: Why does breathing happen?
 ONLY acceptable answer: The RULE: Volume
changes lead to pressure changes which lead
to the flow of gases to equalize the pressure
Boyle’s
Law =
Pressure &
Volume
have an
INVERSE
relationship
.
 Main inspiratory muscles
 Diaphragm & external intercostals
 Thoracic dimensions change to increase
volume of thoracic cavity by 0.5 liters
 Intrapulmonary pressure drops 1-3 mmHg
and air rushes info normal quiet inspiration
 A deep forced (active) inspiration requires
activation of accessory muscles – see diagram
in notes
 A passive process dependent on natural lung
elasticity
 lungs recoil when inspiration stops – so
alveoli compress –which leads to a volume
 decreases -causing intrapulmonary pressure
to rise - gas outflows to equalize the
pressure with atmospheric pressure
 Forced (active) expiration requires contraction
of abdominals, etc – see diagram
 Bronchial sounds: produced by air rushing
through trachea & bronchi
 Vesicular sounds: produced by air filling
alveoli
 Wheezing:
whistling
sound
 Rales:
rasping
sound
 Basic Lung Sounds – Bronchial
 Auscultating The Lungs - Reference Guide
 Pulmonary ventilation can be influenced by 4
physical factors




Respiratory passage resistance
Lung compliance
Lung elasticity
Alveolar surface tension forces
 Resistance due to
increased friction
as air moves
through passages
 Smooth muscle
bronchoconstriction
Disorders such as
asthma – when
bronchi constrict
 Local accumulations
of mucus, infectious
material, and tumors
– also block air
passage
Condition
where the
bronchi become
inflamed and begin to
close down.
Causes individual to
have trouble
breathing, and if
severe enough, may
close down airways.
 The ease with which lungs can readily expand
 Affected by the elasticity of the lungs and the
thoracic cage which can be diminished by 2
main factors:
 Fibrosis of the lung tissue
 Ossification and/or muscle paralysis impairs
flexibility of the thoracic cage
 Essential for normal expiration
 Emphysema: tissue becomes less elastic and
more fibrous
 loss of elasticity & increase in fibrous tissue causes
enormous effort to exhale – at end stages, alveolar
walls break down and surface area is lost for gas
exchange
Surface tension is caused by the tendency of
polar molecules such as water to stick to each
other with hydrogen bonds
 this can cause the walls of the alveoli to stick
together like plastic wrap every time you
exhale.
 Large amounts of energy /effort will be
required to simply re-expand the lungs and
allow you to inhale



Surfactant – interferes with cohesion of water
molecules so less energy needed to expand
lungs – this is one of the things that keeps
our lungs partially expanded at all times. (the
other thing is the pressure difference
previously discussed)
Secreted by Type II cells in lungs
AKA:
Hyaline
Membrane Disease
Caused by lack of
surfactant due to
prematurity
28 weeks of
gestation is
considered