Chapter 13 – Part 2
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
Respiratory Sounds
 Sounds are monitored with a stethoscope
 Bronchial sounds – Produced by air rushing
through trachea and bronchi
 Vesicular breathing sounds – Occur as air
fills the alveoli; soft sounds that resemble a
muffled breeze
 Diseased respiratory tissue, mucus, or pus
can produce abnormal sounds such as rales
(a rasping sound) and wheezing (a whistling
sound)
External Respiration
 External respiration – the actual
exchange of gases between the alveoli
and the blood
 Oxygen movement into the blood
 Because body cells continually remove O2
from the blood, there is always more O2 in
the alveoli than in the blood
 Oxygen moves by diffusion towards the area
of lower concentration
 Pulmonary capillary blood gains oxygen
External Respiration
 Carbon dioxide movement out of the
blood
 Blood returning from tissues has higher
concentrations of carbon dioxide than air in
the alveoli
 Pulmonary capillary blood gives up carbon
dioxide
 Blood leaving the lungs is oxygen-rich
and carbon dioxide-poor
Gas Transport in the Blood
 Oxygen is transported in the blood in two
ways:
1. Most attaches to hemoglobin molecules
inside the red blood cells to form
oxyhemoglobin (HbO2)
2. A very small amount of oxygen is carried
dissolved in the plasma
 Color change in blood
 Oxygen-rich blood = bright red
 Oxygen-poor blood = dark red
Gas Transport in the Blood
 Carbon dioxide transport in the blood
1. Most is transported in the plasma as
bicarbonate ion (HCO3–)
 Plays a very important role in the blood
buffer system
2. A small amount is carried inside red blood
cells on hemoglobin, but at different
binding sites than those of oxygen
Internal Respiration
 Internal respiration - exchange of
gases between blood and body cells
 An opposite reaction to what occurs in
the lungs
 Carbon dioxide diffuses out of tissue to
blood
 Oxygen diffuses from blood into tissue
Internal Respiration
External Respiration,
Gas Transport, and
Internal Respiration
Summary
Hypoxia
 Hypoxia – Inadequate oxygen delivery
to body tissues
 Impaired oxygen transport
 May be the result of anemia, pulmonary
disease, or impaired or blocked blood
circulation
 Symptoms:
 Easy to recognize in fair-skinned people
because their skin and mucosae take on a
bluish cast (become cyanotic)
 In dark-skinned individuals, this color
change can be observed only in the
mucosae and nailbeds.
Carbon Monoxide Poisoning
 Type of hypoxia
 Odorless, colorless gas that
competes vigorously with O2 for the
same binding sites on hemoglobin
 Crowds out or displaces O2 (hemoglobin binds
to carbon dioxide more readily than to oxygen)
 Leading cause of death from fire
 Dangerous because it kills softly and quietly
 Does not produce the characteristic signs of
hypoxia – cyanosis and respiratory distress
 Instead, the victim becomes confused and has a
throbbing headache
Neural Regulation of Respiration
 Activity of respiratory muscles is transmitted
to the brain by the phrenic and intercostal
nerves
 Neural centers that control rate and depth are
located in the medulla
 The pons appears to smooth out respiratory
rate
 Normal respiratory rate (eupnea) is 12–15
respirations per minute
 Hyperpnea is increased respiratory rate
often due to extra oxygen needs (exercise)
Suppressed Medulla Centers
 If the medulla centers
are completely
suppressed,
respiration stops
completely and death
occurs.
 Can occur with an
overdose of
sleeping pills,
morphine, or
alcohol
Neural Regulation of Respiration
Factors Influencing Respiratory
Rate and Depth
1. Physical factors (Increased body temperature, exercise, talking, coughing)
2. Conscious control (during swimming,
swallowing, singing)
•
Voluntary control of breathing is limited and
the respiratory centers will ignore messages
from our wishes when the O2 supply is
getting too low.
3. Emotional factors (Ever been so scared
that you gasped or were nearly panting?)
Factors Influencing Respiratory
Rate and Depth
 Chemical factors
 Carbon dioxide levels
 Level of carbon dioxide in the blood is the
main regulatory chemical for respiration
 Increased carbon dioxide increases
respiration
 Changes in carbon dioxide act directly on
the medulla oblongata
Factors Influencing Respiratory
Rate and Depth
 Chemical factors (continued)
 It is the body’s need to rid itself of
carbon dioxide (not to take in oxygen)
that is the most important stimulus for
breathing in a healthy person.
Factors Influencing Respiratory
Rate and Depth
 Hyperventilation – A rapid and
deep breathing pattern
 Occurs when carbon dioxide or other
sources of acid begin to accumulate in the
blood and the pH starts to drop
 Different breathing pattern from the
hyperpnea of exercise
 This blows off more carbon dioxide, which
returns blood pH to normal
Hyperventilation
 When brought on by anxiety attacks, it often
leads to brief periods of apnea (cessation of
breathing) until the carbon dioxide builds up in
the blood again
 If breathing stops for an extended period of
time cyanosis can occur
 The individual may get dizzy and faint
 Such attacks can be prevented by
having the person breath into a paper
bag (raises the CO2 levels in the blood)
Factors Influencing Respiratory
Rate and Depth
 Hypoventilation – Extremely slow or
shallow breathing
 Occurs when blood starts to become too
basic
 Allows carbon dioxide to accumulate in the
blood and brings blood pH into normal
range