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10/20/16
Chapter 15
Respiratory System
Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
Learning Objectives
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Differentiate between internal and external respiration.
List the secondary functions of the respiratory system.
List the components of the upper respiratory tract and describe
their structure and functions.
List the components of the lower respiratory tract and describe
their structure and functions.
Describe the events that occur during inspiration and expiration.
List the muscles involved in inspiration and expiration.
Define the terms tidal volume, minute volume, and residual
volume.
Describe the processes of oxygen and carbon dioxide exchange
between the alveoli and the blood.
Describe the mechanical and chemical respiratory control systems.
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Respiratory System
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Primary Function: bring O2 into the body
and CO2 out of it
Ø
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Respiratory system works together with the
cardiovascular system
Secondary functions
Phonation (voice production)
Ø Regulation of body temperature
Ø Regulation of acid-base balance
Ø Sense of smell
Ø
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Respiration
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External respiration - exchange of O2 and
CO2 between the inhaled air and the blood
flowing through the pulmonary capillaries
Internal respiration - exchange of O2 and
CO2 between the blood in the systemic
capillaries and all the cells and tissues of
the body
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Structures of Respiratory System
Upper Respiratory
Tract (outside the
lungs)
˜ Nostrils
˜ Nasal passages
˜ Pharynx
˜ Larynx
˜ Trachea
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Nose and Nasal Passages
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Nares (nostrils):
external openings
of the respiratory
tube
Ø
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Lead into the
nasal passages
Nasal Passages:
between the
nostrils and the
pharynx
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Nose and Nasal Passages
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Nasal septum:
separates the left
and right nasal
passage
Hard and soft
palates: separate
the nasal
passages from
the mouth.
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Nose and Nasal Passages
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Turbinates (nasal
conchae):
Divide each nasal
passage into 3
main passageways
Ø Thin, scroll-like
bones covered with
nasal epithelium
Ø Dorsal and ventral
Ø
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Nose and Nasal Passages
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Nasal passages lined
with pseudostratified
columnar epithelium
Cilia project from the
cell surfaces up into a
layer of mucus
Mucus is secreted by
mucous glands and
goblet cells
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Nasal Passages Functions
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Warm, humidify, and filter inhaled air
Air is warmed by blood flowing through blood
vessels just beneath the nasal epithelium.
Air is humidified by mucus and other fluids on the
epithelial surface.
Air is filtered as it passes through the winding
passages produced by the turbinates.
Ø Particles do not readily pass through but
become trapped in the mucous layer; cilia
move mucus and trapped foreign material
upward to the pharynx, mouth
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Paranasal Sinuses
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Paranasal Sinuses:
ciliated outpouchings
of the nasal passages
contained within
spaces in certain skull
bones
Most animals have
two frontal sinuses
and two maxillary
sinuses within the
frontal and maxillary
bones
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Pharynx
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Common passageway for respiratory and
digestive systems
Soft palate divides pharynx into the dorsal
nasopharynx (respiratory passageway)
and the ventral oropharynx (digestive
passageway)
Caudal end of pharynx opens dorsally into
the esophagus and ventrally into the larynx
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Pharynx
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Reflexes control actions of the muscles around
the pharynx.
Larynx and pharynx work together to prevent
swallowing from interfering with breathing, and
vice versa.
Swallowing - breathing stops, opening into larynx
is covered, material to be swallowed moves to
rear of pharynx, esophagus opens
After swallowing, larynx is reopened and
breathing resumes
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Larynx
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Short, irregular tube connecting pharynx
with the trachea
Composed of segments of cartilage that
are connected to each other and the
surrounding tissues by muscles
Supported in place by the hyoid bone
Cartilage components - epiglottis,
arytenoid cartilages, thyroid cartilage,
cricoid cartilage
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Larynx Cartilages
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Epiglottis - single, leaf-shaped; projects
forward from the ventral portion of the
larynx
Ø
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During swallowing, the epiglottis is pulled back
to cover the opening of the larynx
Arytenoid cartilages - paired; attachment is
the site of the vocal cords
Muscles adjust the tension of the vocal cords
by moving the cartilages.
Ø Arytenoid cartilages and the vocal cords form
the boundaries of the glottis.
Ø
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Larynx Functions
Voice Production
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Vocal cords - two connective tissue bands
attached to the arytenoid cartilages
Ø
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Stretched across lumen of larynx parallel to each other
Vocal cords vibrate as air passes over them.
Muscles attached to the arytenoid cartilages
control the tension of the vocal cords.
Ø
Ø
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Complete relaxation opens the glottis wide; no sound
Lessening the tension produces lower-pitched sounds
Tightening the tension produces higher-pitched sounds
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Larynx Function
Prevention of foreign material being inhaled
Ø
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During swallowing, muscle contractions pull
the larynx forward and fold the epiglottis back
over its opening.
Control airflow to and from the lungs
Ø
Small adjustments in the size of the glottis aid
movement of air.
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Trachea
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Short, wide tube
Extends from the larynx into the thorax
Divides into the two main bronchi that
enter the lungs
Ø
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Bifurcation of the trachea
Composed of fibrous tissue and smooth
muscle held open by hyaline cartilage
rings
Lined with ciliated epithelium
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Trachea
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C-shaped rings of
hyaline cartilage
Open part of
tracheal rings face
dorsally
Gap between the
ends of each ring
bridged by smooth
muscle
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Structures of Respiratory System
Lower Respiratory Tract
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Bronchi
Bronchioles
Alveolar ducts
Alveoli
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Bronchial Tree
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Each bronchus
divides into
smaller bronchi,
which divide into
even smaller
bronchi, and then
tiny bronchioles
Bronchioles
subdivide into
alveolar ducts
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Bronchial Tree
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Alveolar ducts end
in groups of alveoli
Arranged like
bunches of grapes
Alveolar sacs:
groups of alveoli
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Bronchial Tree
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Autonomic nervous system controls smooth
muscle fibers in wall of bronchial tree
Bronchodilation - bronchial smooth muscle
relaxes
Ø Aids respiratory effort during intense physical
activity
Bronchoconstriction - bronchial smooth muscle
partially contracts
Ø Reduces size of the air passage
Ø Irritants in inhaled air can cause
bronchoconstriction
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Alveoli
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Site of external
respiration
Tiny, thin-walled
sacs of simple
squamous
epithelium
Surrounded by
networks of
capillaries
Lined with fluid that
contains surfactant
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Lungs
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Each lung has a
base, an apex, and a
convex lateral
surface.
Base is in caudal part
of thoracic cavity
Ø Lies directly on
cranial surface of
diaphragm
Apex lies in cranial
portion of thoracic
cavity
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Lungs
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Convex lateral
surface lies
against inner
surface of the
thoracic wall
Mediastinum area between the
lungs
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Lungs
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Lungs are divided into lobes (in most
species)
Ø
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Pattern varies with species
Lobes are distinguished by the major
branches of the bronchi
Hilus - small, well-defined area on medial
side of lung
Ø
Site where air, blood, lymph, and nerves enter
and leave the lung
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Pulmonary Circulation
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Deoxygenated blood enters the lungs from
right ventricle of heart through the
pulmonary artery
Pulmonary artery splits into left and right
pulmonary arteries that enter the two lungs
Ø Pulmonary arterioles enter capillary networks
around the alveoli
Ø
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Oxygenated blood returns to the left side
of heart in the pulmonary veins.
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Thoracic Cavity
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Bound by thoracic
vertebrae dorsally,
ribs & intercostal
muscles laterally, the
sternum ventrally
Mediastinum – area
between lungs
Ø
Contains heart,
trachea, esophagus,
blood vessels, nerves,
lymphatic structures
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Pleura
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Thin membrane that lines thoracic cavity
and covers organs and structures in the
thorax
Visceral layer covers thoracic organs and
structures
Ø Parietal layer lines the cavity
Ø
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Space between the two pleural layers is
filled with a small amount of pleural fluid
Ø
Helps ensure that surfaces of organs slide
smoothly along the lining of the thorax during
breathing
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Diaphragm
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Thin, dome-shaped
skeletal muscle sheet
Forms caudal
boundary of thorax
Important respiratory
muscle
Flattens when it
contracts
Ø Enlarges volume of
the thorax and aids
inspiration
Ø
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Process of Respiration
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Pressure within the thorax is negative with
respect to atmospheric pressure.
Pulls lungs tight out against the thoracic wall
Ø Lungs follow passively as movements of the
thoracic wall and diaphragm alternately
enlarge and reduce the volume of the thorax.
Ø Negative intrathoracic pressure helps draw
blood through veins and into the atria
Ø
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Inspiration
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Process of drawing air into lungs
(inhalation)
Results from enlargement of the volume of
the thoracic cavity by the inspiratory
muscles
Main inspiratory muscles: diaphragm and
external intercostal muscles
Ø
External intercostal muscles located in the
external portion of the intercostal spaces
(between ribs)
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Expiration
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Process of pushing air out of lungs (exhalation)
Results from decrease in size of thoracic cavity
Main expiratory muscles: internal intercostal
muscles and abdominal muscles
Ø Internal intercostal muscles located between
the ribs, deep to the external intercostal
muscles
Contraction of abdominal muscles pushes
abdominal organs against the diaphragm and
pushes diaphragm back into its full dome shape.
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Respiratory Volumes
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Tidal volume - volume of air inspired and
expired during one breath
Ø
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Varies according to the body's needs
Minute volume - volume of air inspired and
expired during 1 minute of breathing
Residual volume - volume of air remaining
in the lungs after maximum expiration
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Alveolar Gas Exchange
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Simple diffusion of gas molecules
according to concentration gradient
O2 diffuses from the alveolar air into the
blood of the alveolar capillary
CO2 diffuses from the blood into the
alveolus
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Partial Pressure of Gases
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Pressure of each individual gas in a mixture of
gases
Example:
Ø
Ø
Ø
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Atmospheric air ~ 21% O2
Total atmospheric pressure ~ 760 mm of mercury (Hg)
Partial pressure of oxygen (PO2) in atmosphere:
21% × 760 mm Hg = 159.6 mm Hg
Partial pressures of O2 and CO2 in the blood of
alveolar capillaries is determined by the partial
pressures of O2 and CO2 in alveolar air
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Respiratory Center
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Area in the medulla oblongata of the brain
stem
Controls respiratory muscle contractions
Ø
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Directs timing and strength of contraction
Individual control centers - inspiration,
expiration, breath holding
Can be consciously controlled for brief
periods
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Mechanical Control System
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Stretch receptors in the lungs set limits on routine
resting inspiration and expiration.
Respiratory center sends out nerve impulses
when lungs inflate to a certain point
Ø Stops muscle contractions that produce
inspiration and starts contractions to produce
expiration
Another set of nerve impulses sent when lungs
deflate sufficiently
Ø Stops expiration and starts the process of
inspiration again
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Chemical Control System
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Adjusts the normal rhythmic breathing
pattern produced by the mechanical
control system
Chemical receptors in carotid artery and
aorta monitor blood CO2, pH, and O2
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Chemical Control System
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Blood level of CO2 and blood pH are
usually linked
Increased CO2 in blood and decreased
blood pH triggers respiratory center to
increase rate and depth of respiration
Decreased CO2 in blood increases blood
pH; increased blood pH level triggers
respiratory center to decrease rate and
depth of respiration
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Clinical Applications
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Sinusitis
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Endotracheal Intubation
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Roaring in Horses
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Aspiration Pneumonia
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Clinical Applications
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Tracheal Collapse
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Asthma
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Respiratory Tract Infections
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Pneumothorax and Lung Collapse
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Clinical Applications
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Coughs, Sneezes, Yawns, Sighs, and
Hiccups
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