Lecture 18
The Respiratory System
 Overview of the Respiratory System
o Functions:
 Provides ______________ and carbon dioxide exchange
 Serves for ______________ and other vocalizations (laughing,
crying)
 Provides the sense of smell, which is important in social
integration, food selection, and avoiding danger (such as spoiled
food or a gas leak)
 Breathing creates blood pressure gradients between the thorax and
abdomen that promote the flow of ___________ and venous blood
 Taking a deep breath and holding it contracts the abdominal
muscles helps to expel abdominal contents during urination,
defecation, and _____________________
o Divisions:
 Conducting division
 Passages that serve only for airflow
 Nostrils through _________________
 Respiratory division
 Consists of the _________________ and other distal gasexchange regions
 The Upper Respiratory Tract
o The Nose
 The nose has several functions
 It warms, _______________, and humidifies the air
 It detects odors in the airstream
 It serves as a resonating chamber that amplifies the voice
 It extends from a pair of anterior openings called the nostrils
(external nares) to a pair of posterior opening called the posterior
______________ (choanae)
 The nasal cavity is divided into right and left halves called nasal
__________________
 The separation between the right and left nasal fossa is the nasal
septum
 The facial part of the nose is shaped by ___________ and hyaline
cartilage
 The superior part is shaped by the nasal bones and maxilla
 The inferior part is shaped by lateral cartilage (below the
nasal bones) and alar cartilage (surrounding the nostrils)
 The nasal cavity begins with a chamber called the nasal
______________
 This space is lined with stratified squamous epithelium like
the facial skin, and has stiff ________________ (hairs) that
block insects and large airborne particles from the nose

The nasal septum:
 The vomer forms the ______________ part
 The perpendicular plate of the ethmoid bone supports the
superior part
 Much of the space inside the nasal cavity is occupied by the nasal
conchae (superior, middle, and inferior)
 They project from the lateral walls towards the septum
 Beneath each of the conchae is a narrow _____________
passage
 The narrow space between the conchae forces most of the
air to come in contact with the mucous membrane
o Most dust in the air sticks to the mucus
o The air picks up moisture and __________ from the
mucosa
o The conchae clean, warm, and moisten the air
 The rest of the nasal cavity is covered in ciliated
pseudostratified respiratory mucosa
o It consists of goblet cells that secrete mucus and
ciliated cells which drive the mucus toward the
posterior ________________ and into the pharynx
o Pollen, dust, and other inhaled particles stick to the
________________, and lysozyme in the mucus
destroys bacteria
o The Pharynx
 The pharynx is a muscular funnel extending from the choanae to
the larynx
 It has three regions
 The _____________________ lies posterior to the choanae
o It receives the auditory tubes from the middle ears
o It houses the pharyngeal tonsil
o Inhaled air turns downward ________ degrees
 Relatively large particles generally cannot
make that turn and collide with the posterior
wall, where it sticks to the mucosa near the
tonsil
 The oropharynx is a space between the soft palate and the
root of the _______________
o It extends inferiorly as far as the hyoid bone
o It contains the lingual and ________________
tonsils
 The laryngopharynx begins at the level of the hyoid bone
o It passes inferiorly and dorsal to the larynx and ends
at the opening of the esophagus, at the level of the
___________________ cartilage of the larynx
o The Larynx
 The larynx is the voicebox
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


It is a cartilaginous chamber about 4 cm long
Its primary function is to keep food and drink out of the airway
It also produces sounds in many animals, and ______________ in
humans
The glottis is the superior opening of the larynx
 The epiglottis is flap of tissue that guards the glottis
o At rest, the epiglottis stands almost
________________
o During swallowing, the extrinsic muscles of the
larynx pull the larynx upward toward the ipiglottis,
and the tongue pushes the epiglottis downward
toward to meet it
o The epiglottis directs food and drink into the
esophagus dorsal to the airway
The larynx consists of nine cartilages
 The epiglottic cartilage is the most ______________
cartilage
o It’s a spoon-shaped cartilage in the tissue of the
epiglottis
 The ____________________ cartilage is the largest
cartilage
o It’s named for its shield-like shape
o It broadly covers the anterior and lateral aspects of
the larynx
o The Adam’s apple is an anterior peak of the thyroid
cartilage
 Testosterone stimulates the growth of the
cartilage, so it is larger in ______________
 The cricoid cartilage is inferior to the thyroid cartilage
o It’s ring-like in construction and connects the larynx
to the ___________________
 The arytenoid cartilages are posterior to the thyroid
cartilage
 The corniculate cartilages are a pair of little horns at the
upper ends of the ___________________ cartilages
 The cuneiform cartilages support soft tissues between the
arytenoids and the epiglottis
The interior wall of the larynx has two folds on each side that
stretch from the thyroid cartilage in front to the arytenoid cartilage
in the back
 The vestibular folds are the superior pair
o They close the ________________ during
swallowing
 The vocal folds are the inferior pair
o They produce sound when air passes between them

o Intrinsic muscles control the vocal cords by pulling
on the ____________________ and arytenoids
cartilages, causing the cartilages to pivot
o When pulled taut, they produce ______________
pitch
The Lower Respiratory Tract
o The Trachea
 The windpipe is a tube about 12 cm long and 2.5 cm in diameter
 It is supported by rings of hyaline cartilage
 The inner lining is pseudostratified columnar epithelium
 It’s composed of mucus-secreting _________________
cells, ciliated cells, and short basal stem cells
 The mucus traps inhaled particles, and the cilia drives the
debris-laden mucus toward the pharynx where it is
_________________
o The Bronchi
 The primary bronchi are forks branching to the right and left from
the ____________________
o The Lungs
 Each lung is somewhat conical with a concave base resting on the
diaphragm and a blunt peak called the ____________ projecting
above the clavicle
 The costal surface is the portion pressed against the ribcage
 The mediastinal surface is the portion the faces medially
 The hilum is a slit in the __________________ surface through
which the primary bronchus, blood vessels, and nerves enter the
lung
 The right lung is shorter than the left because the liver rises higher
on the right
 It has three lobes (superior, middle, and inferior)
 The left lung is taller but narrower
 On the medial surface, there is a cardiac impression, where
the _________________ presses against it
 It has only two lobes (superior and inferior)
 Within each lung, there is a bronchial tree
 Branching from the trachea into the two lungs there are
primary bronchi
 After entering the lung the primary bronchus branches into
one __________________ bronchus for each lobe of the
lung
 Each secondary bronchus divides into tertiary bronchi
 Bronchioles are continuations of the airway that lack supportive
cartilage and are 1 mm or less in diameter
 Each bronchiole divides into terminal bronchioles, the final
branches of the conducting division
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
Each terminal bronchiole gives off two or more smaller
_______________________ bronchioles
 Each respiratory bronchiole divides into thin-walled passages
called alveolar ducts.
 The alveolar ducts end in alveolar _________ which are grapelike
cluster of alveoli
 There are _______________ networks around each
alveolus, for the exchange of CO2 and O2
o The Pleurae
 The surface of the lung is covered by a serous membrane called the
visceral pleura
 At the hilum, the visceral pleura turns back on itself and forms the
________________ pleura
 The space between the parietal pleurae and visceral pleurae is
called the pleural cavity
 The pleural cavity contains a slippery pleural ______________
 The pleurae and pleural fluid have 3 functions
 Reduction of friction
o The fluid acts as a __________________ that
enables the lungs to expand and contract with
minimal friction
 Creation of pressure gradient
o During inspiration (inhalation) the rib cage expands
and draws the parietal pleura outward along with it
o The visceral pleura clings to the parietal pleura, and
since the visceral pleura is the lung surface, its
outward movement _________________ the lung
 Compartmentalization
o The pleurae, mediastinum, and pericardium
compartmentalize the thoracic organs and prevent
____________________ of one organ from
spreading easily to neighboring organs
Neuromuscular Aspects of Respiration
o Inspiration
 The ___________________ does most of the work of inspiration
(inhalation)
 It’s controlled by the phrenic nerves
 It drops about 1.5 cm in quiet inspiration
 It drops up to 7 cm in forced inspiration (___________
breathing)
 The external intercostals muscles are also important in inspiration
 They are innervated by the intercostal nerves
 The scalenes fix the first pair of ribs and the external
intercostals lift the remaining ribs
o They swing up and out, ____________________
the volume of the thoracic cavity

o It creates a pressure gradient that draws air into the
lungs
Deep inspiration is further aided by the pectoralis minor,
________________________, and erector spinae muscles
o Expiration
 Normal expiration is achieved by the elasticity of the lungs and
thoracic cage
 As structures recoil, the thoracic cage diminishes in size,
the air pressure in the lungs rises above the atmospheric
pressure, and the air flows _____________
 The only muscular effort involved in expiration is a braking
action to keep the lungs from recoiling too _____________
 Forced expiration (to blow out the candles) employs internal
intercostals and abdominal muscles
 The internal intercostals muscles depress the ribs
 The internal and external abdominal obliques, transverse
abdominis, and rectus abdominis compress the abdominal
organs, raise the intra-abdominal pressure, and push the
viscera up against the __________________
o Respiration Centers of the Brainstem
 Rhythm of unconscious breathing is caused by nuclei in the
reticular formation of the medulla oblongata and pons
 In the medulla, these nuclei include:
 inspiratory neurons of the inspiratory center which fire
during ___________________
 expiratory neurons of the expiratory center fire during
expiration
 The pons contains respiratory nuclei
 The lower pons has an ___________________ center
whose function seems to prolong inspiration
 The upper pons has a pneumotaxic center which sends a
continual stream of signals to the inspiratory center of the
medulla
o It regulates the duration and _______________ of
each breath
 Respiratory centers receive input from several sources
 Chemoreceptors respond to pH and CO2 and O2
concentrations of the blood and cerebrospinal fluid
o Peripheral chemoreceptors are found in the aortic
bodies and _______________ bodies
o Central chemoreceptors are found close to the
surface of the medulla oblongata
 Stretch receptors in the bronchial tree monitor inflation of
the lungs
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The vagus nerves transmits singals from the respiratory
__________________ when they are stimulated by irritants
in the airway
Higher brain centers allow for conscious control over
breathing