Part II - Respiratory
Physiology
4 distinct events
 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
External Respiration
Resp. Gas Transport
Internal Respiration
Cellular Respiration
Mechanics of Breathing
Pulmonary Ventilation: Event #1
 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
Pressure Relationships
 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
Atalectasis
 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
Atelectasis
term for lung collapse
Pneumothorax
Air in the intrapleural
space due to trauma –
causes lung collapse
Pulmonary ventilation
 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
Diaphragm Structure
Boyle’s
Law =
Pressure &
Volume
have an
INVERSE
relationship
.
Pressure differences cause gas to flow from
high to low
When the diaphragm contracts, the
muscle fibers shorten – so muscle
comes down
Inspiration
 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 in for normal quiet
inspiration
 A deep forced (active) inspiration requires
activation of accessory muscles – see
diagram in notes
Expiration
 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
What doctors listen for
 Bronchial sounds: produced by air rushing
through trachea & bronchi
 Vesicular sounds: produced by air filling
alveoli
Respiratory Sounds
 Wheezing
: whistling
sound
 Rales:
rasping
sound
Hear the sounds
 Basic Lung Sounds – Bronchial
 Auscultating The Lungs - Reference Guide
Physical factors influencing
 Pulmonary ventilation can be influenced
by 4 physical factors




Respiratory passage resistance
Lung compliance
Lung elasticity
Alveolar surface tension forces
Respiratory passage resistance
 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
Asthma
Lung compliance
 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
Lung fibrosis
Lung Elasticity
 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
Alveolar Surface Tension forces
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 (IRDS)
Alveolar Surface Tension Forces
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
Alveoli & Surface Tension
IRDS – Infant Respiratory Distress
Syndrome
AKA: Hyaline
Membrane Disease
Caused by lack of
surfactant due to
prematurity
28 weeks of gestation is
considered