Chapter 13 – Part 3
The Respiratory System
Events of Respiration
 The major function of the respiratory
system is to supply the body with O2 and
to dispose of CO2.
 To do this, at least four events must occur
(collectively called respiration):
1. Pulmonary ventilation
2. External respiration
3. Respiratory gas transport
4. Internal respiration
Events of Respiration
1. Pulmonary ventilation – moving air in
and out of the lungs
 Commonly called breathing
2. External respiration – gas exchange
between pulmonary blood and alveoli
 O2 loading and CO2 unloading
Events of Respiration
3. Respiratory gas transport – transport
of oxygen and carbon dioxide via the
bloodstream to and from the lungs and
body tissues
4. Internal respiration –
gas exchange between
blood and tissue cells in
systemic capillaries
Mechanics of Breathing
(Pulmonary Ventilation)
 Completely
mechanical process
 Depends on volume
changes in the
thoracic cavity
Mechanics of Breathing
(Pulmonary Ventilation)
 Volume changes lead to pressure
changes, which lead to the flow of gases
to equalize pressure
 A gas always conforms to the shape of its
container
 In a large volume, the pressure will be low.
 If the volume is reduced, the gas molecules
will be closer together and the pressure will
rise.
Mechanics of Breathing
(Pulmonary Ventilation)
 Two phases
1. Inspiration – flow of air into the lungs
2. Expiration – air leaving the lungs
Inspiration (Inhalation)
 Diaphragm and intercostal
muscles contract resulting in
the increased size of the
thoracic cavity
 As the diaphragm contracts, it moves
inferiorly and flattens out
 Contraction of the intercostals lifts the rib
cage and thrusts the sternum forward
Inspiration (Inhalation)
 The increased volume results in a
decreased gas pressure within the lungs,
which produces a partial vacuum
 External air is pulled into the lungs due to
an increase in intrapulmonary volume
 Air continues to pull into the lungs until the
intrapulmonary pressure equals the
atmospheric pressure.
Inspiration (Inhalation)
Exhalation (Expiration)
 Largely a passive process
which depends on natural
lung elasticity
 As muscles relax, air is pushed out of the
lungs
 Forced expiration can occur mostly by
contracting internal intercostal muscles to
depress the rib cage
Exhalation (Expiration)
Pressure Differences in the
Thoracic Cavity
 Normal pressure within the pleural
space (intrapleural pressure) is always
negative
 Differences in lung and pleural space
pressures keep lungs from collapsing
 If for any reason, the intrapleural pressure
becomes equal to the atmospheric
pressure, the lungs will collapse
Atelectasis
 Atelectasis – lung collapse
 The lung is useless for
ventilation
 Usually occurs when air
enters the pleural space from:
1. A chest wound
2. A rupture of the visceral pleura
 Is reversed by drawing air out of the
intrapleural space with chest tubes, which
allows the lungs to re-inflate and resume its
normal function
Nonrespiratory Air Movements
 Can be caused by reflexes or
voluntary actions
 Examples
 Cough - Clears the lower respiratory
passages of debris
 Sneeze – Clears the upper
respiratory passages of debris
 Laughing
 Crying
 Yawn – Increases ventilation to the
lungs; May be initiated by a need to
increase oxygen levels in the blood
 Hiccup – Sudden inspiration; Results
from spasms of the diaphragm
Respiratory Volumes and Capacities
 Tidal volume (TV) – Amount of air
inhaled of exhaled with a normal breath
 Normal breathing moves about 500 ml of air
(about a pint) with each breath
 Many factors that affect respiratory capacity
1. A person’s size
2. Sex
3. Age
4. Physical condition
Respiratory Volumes and Capacities
 Inspiratory reserve volume (IRV) Amount of air that can be taken in forcibly
over the tidal volume
 A person can inhale much more air than is
taken in during a normal, or tidal, breath
 Usually between 2100 and 3200 ml
Respiratory Capacities
Respiratory Volumes and Capacities
 Expiratory reserve volume (ERV) Amount of air that can be forcibly
exhaled
 After a normal
expiration, more
air can be
exhaled
 Approximately
1200 ml
Respiratory Volumes and Capacities
 Residual volume - Air remaining in the
lungs after expiration
 Even after the most strenuous expiration,
about 1200 ml of air still remains in the lungs
 The residual volume cannot be voluntarily
expelled
 Is important because:
1. It allows gas exchange to go on
continuously even between breaths
2. It helps to keep the alveoli open
(inflated)
Respiratory Capacities
Respiratory Volumes and Capacities
 Vital capacity - the total amount of
exchangeable air
 Vital capacity = TV + IRV + ERV
 Typically around 4800 ml in healthy young
males
Respiratory Volumes and Capacities
Dead space volume - Air that remains
in conducting zone and never reaches
alveoli
 About 150 ml in a normal tidal breath
 Functional volume - Air that actually
reaches the respiratory zone and
contributes to gas exchange
 Usually about 350 ml
Respiratory Volumes and Capacities
 Respiratory capacities
are measured with a
spirometer
 As a person breathes,
the volumes of air
exhaled can be read on an indicator
 Spirometer testing is useful for evaluating
losses in respiratory functioning and in
following the course of some respiratory
diseases