Respiratory system

Respiratory system


At the end of this lecture, student will be able to

• Enumerate structural classification

• Illustrate functional portions of respiratory system

• Describe the anatomy of the nose, pharynx.

• Describe the anatomy of the larynx, trachea

• Describe the structure involved in sound production

• Explain the process of breathing

• Discuss the structure of alveoli

• Outline lung volumes and capacities

• Describe the exchange of oxygen and carbon dioxide in
internal and external respiration

• Describe how the blood transports oxygen and carbon

• Explain how the nervous system controls breathing

• Discuss different disorders of respiratory tract


• Structural system and functional portions of respiratory

• Anatomy of the nose, pharynx.

• Anatomy of larynx and trachea

• Structure involved in sound production

• Process of breathing

• Structure of alveoli

• Lung volumes and capacities

• Exchange of oxygen and carbon dioxide during respiration

• Nervous system and controls breathing

• Factors altering rate and depth of breathing

• Disorders of respiratory system

and Functions of the Respiratory System


– Upper respiratory tract

– Lower respiratory tract.

• Functional

– Conducting portion: transports air.

   • Nose

   • Nasal cavity

   • Pharynx

   • Larynx

   • Trachea

   • Progressively
smaller airways, from the primary bronchi to the bronchioles

– Respiratory portion: carries out gas exchange.

   • Respiratory

   • Alveolar ducts

   • Air sacs called

• Upper respiratory tract is all conducting

• Lower respiratory tract has both conducting and
respiratory portions

System Functions

• Breathing
(pulmonary ventilation):

– consists of two cyclic phases:

     • Inhalation,
also called inspiration

     • Exhalation,
also called expiration

– Inhalation draws gases into the lungs.

– Exhalation forces gases out of the lungs.

• Gas exchange: O2
and CO2

– External respiration

     • External
environment and blood

– Internal respiration

     • Blood and cells

• Gas conditioning:

– Warmed

– Humidified

– Cleaned off particulates

• Sound production:

– Movement of air over true vocal cords

– Also involves nose, paranasal sinuses, teeth, lips and

• Olfaction:

– Olfactory epithelium over superior nasal conchae

• Defense:

– Course hairs, mucus, and lymphoid tissue

Upper Respiratory Tract

• Composed of

– The nose

– The nasal cavity

– The paranasal sinuses

– The pharynx (throat)

– And associated structures.

• All part of the conducting portion of the respiratory


• Paranasal sinuses:

– In four skull bones

– paired air spaces

– decrease skull bone weight

Named for the bones
in which they are housed.

– Frontal

– ethmoidal

– sphenoidal

– Maxillary

• Communicate with the nasal cavity by ducts.

• Covered with the same pseudostratified
ciliated columnar epithelium
as the nasal cavity.


• Common to both the respiratory and digestive systems.

• Commonly called the throat.

• Funnel-shaped – Slightly wider superiorly and narrower

• Originates posterior to the nasal and oral cavities

• Extends inferiorly near the level of the bifurcation of
the larynx and esophagus.

• Common pathway for both air and food.

• Walls:

– lined by a mucosa

– contain skeletal muscles primarily used for swallowing.

• Flexible lateral walls

– Distensible

– To force swallowed food into the esophagus.

• Partitioned into three adjoining regions:

– Nasopharynx

– Oropharynx

– Laryngopharynx


• Superiormost region of the pharynx.

• Location:

– Posterior to the nasal cavity

– Superior to the soft palate

• separates it from the posterior part of the oral cavity.

• Normally, only air passes through.

• Soft palate

– Blocks material from the oral cavity and oropharynx

– elevates when we swallow.

• Auditory tubes

– paired

– In the lateral walls of the nasopharynx

– connect the nasopharynx to the middle ear.

• Pharyngeal tonsil

– Posterior nasopharynx wall

– Single

– Commonly called the adenoids.


   The middle
pharyngeal region.


– Immediately posterior to the oral cavity.

– Bounded by the soft palate superiorly,

– The hyoid bone inferiorly.

• Common respiratory and digestive pathway

– Both air and swallowed food and drink pass through.

• 2 pairs of muscular

– Anterior palatoglossal arches

– Posterior palatopharyngeal arches

– Form the entrance from the oral cavity.

   Lymphatic organs

– provide the first line of defense against ingested or
inhaled foreign materials.

Palatine tonsils – On
the lateral wall between the arches

Lingual tonsils – At
the base of the tongue.


• Inferior, narrowed region of the pharynx.

• Location:

– Extends inferiorly from the hyoid bone

– is continuous with the larynx and esophagus.

– Terminates at the superior border of the esophagus

• is equivalent to the inferior border of the cricoid
cartilage in the larynx.

• The larynx (voice box) forms the anterior wall

• Lined with a nonkeratinized stratified squamous epithelium
(mucus membrane)

• Permits passage of both food and air.

Lower Respiratory Tract

• Conducting portion

– Larynx

– Trachea

– Bronchi

– Bronchioles and their associated structures

• Respiratory portion
of the respiratory system

– Respiratory bronchioles

– Alveolar ducts

– Alveoli


• Short, somewhat cylindrical airway

• Location:

– Bounded posteriorly by the laryngopharynx,

– Inferiorly by the trachea.

• Prevents swallowed materials from entering respiratory

• Conducts air into the lower respiratory tract.

• Produces sounds.

• Nine pieces of

– Three individual pieces

       • Thyroid

       • Cricoid

       • Epiglottis

– Three cartilage pairs

       • Arytenoids:
on cricoid

       • Corniculates:
attach to arytenoids

       • Cuniforms:in
aryepiglottic fold

– held in place by ligaments and muscles.

       • Intrinsic
muscles: regulate tension on true vocal cords

       • Extrinsic muscles: stabilize the larynx


• Two pairs of ligaments

• Inferior ligaments, called vocal ligaments

– covered by a mucous membrane

– Vocal folds: ligament and mucosa.

– are true vocal cords

     • They produce
sound when air passes between them

• Superior ligaments, called vestibular ligaments

– Covered by mucosa

– Vestibular folds: ligament and mucosa

– Are false vocal cords

     • No function in
sound production

     • protect the
vocal folds.

– The vestibular folds attach to the corniculate cartilages.

• The tension, length, and position of the vocal folds
determine the quality of the sound.

– Longer vocal folds produce lower sounds

– More taunt, higher pitch

– Loudness based on force of air

• Rima glottidis:
opening between the vocal folds

• Glottis: rima
glottidis and the vocal folds


• A flexible, slightly rigid tubular organ

– Often referred to as the windpipe.

• Extends through the mediastinum

– Immediately anterior to the esophagus

– Inferior to the larynx

– Superior to the primary bronchi of the lungs.

• Anterior and lateral walls of the trachea are supported by
15 to 20 C-shaped tracheal cartilages.

– Cartilage rings reinforce and provide some rigidity to the
tracheal wall to ensure that the trachea remains open (patent) at all times

– Cartilage rings are connected by elastic sheets called
anular ligaments.

• At the level of the sternal angle, the trachea bifurcates into
two smaller tubes, called the right and left primary bronchi.

• Each primary bronchus projects laterally toward each lung.

• The most inferior tracheal cartilage separates the primary
bronchi at their origin and forms an internal ridge called the carina.


• A highly branched system

– Air-conducting passages

– originate from the left and right primary bronchi.

• Progressively branch into narrower tubes as they diverge throughout
the lungs before terminating in terminal bronchioles.

• Primary bronchi

– Incomplete rings of hyaline cartilage ensure that they
remain open.

– Right primary bronchus

                  • Shorter,
wider, and more vertically oriented than the left primary bronchus.

– Foreign particles are more likely to lodge in the right
primary bronchus.

– enter the hilum of each lung

– Also entering hilum:

                 • Pulmonary

                 • Lymphatic

                 • Nerves.

   Secondary bronchi (or lobar bronchi)

– Branch of primary bronchus

– Left lung:

                 • Two

                 • Two secondary bronchi

– Right lung

                 • Three

                 • Three
secondary bronchi.

   Tertiary bronchi (or segmental bronchi)

– Branch of secondary bronchi

– Left lung is supplied by 8 to 10 tertiary bronchi.

– Right lung is supplied by 10 tertiary bronchi

– Supply a part of the lung called a bronchopulmonary

Bronchioles, Alveolar Ducts, and Alveoli

• Contain small saccular outpocketings called alveoli.

• An alveolus is about 0.25 to 0.5 millimeter in diameter.

• Its thin wall is specialized to promote diffusion of gases
between the alveolus and the blood in the pulmonary capillaries.

• Gas exchange can take place in the respiratory bronchioles
and alveolar ducts as well as in the lungs, which contain approximately 300–400
million alveoli.

• The spongy nature of the lung is due to the packing of
millions of alveoli together.

Anatomy of the Lungs

• Each lung has a conical shape.

• Its wide, concave base rests upon the muscular diaphragm.

• Its relatively blunt superior region, called the apex or
(cupola), projects superiorly to a point that is slightly superior and
posterior to the clavicle.

• Both lungs are bordered by the thoracic wall anteriorly, laterally,
and posteriorly, and supported by the rib cage.

• Toward the midline, the lungs are separated from each
other by the mediastinum.

• The relatively broad, rounded surface in contact with the
thoracic wall is called the costal surface of the lung.

Pleura and
Pleural Cavities

• The outer surface of each lung and the adjacent internal thoracic
wall are lined by a serous membrane called pleura, which is formed from simple
squamous epithelium.

• The outer surface of each lung is tightly covered by the visceral
pleura, while the internal thoracic walls, the lateral surfaces of the
mediastinum, and the superior surface of the diaphragm are lined by the
parietal pleura.

• The parietal and visceral pleural layers are continuous at
the hilum of each lung.

• The outer surface of each lung is tightly covered by the
visceral pleura, while the internal thoracic walls, the lateral surfaces of the
mediastinum, and the superior surface of the diaphragm are lined by the
parietal pleura.

• The potential space between these serous membrane layers
is a pleural cavity.

• The pleural membranes produce a thin, serous fluid that circulates
in the pleural cavity and acts as a lubricant, ensuring minimal friction during


• Lymph nodes and vessels are located within the connective tissue
of the lung as well as around the bronchi and pleura.

• The lymph nodes collect carbon, dust particles, and
pollutants that were not filtered out by the pseudostratified ciliated columnar

Thoracic Wall
Dimensional Changes during Respiration

• Lateral dimensional changes occur with rib movements.

• Elevation of the ribs increases the lateral dimensions of
the thoracic cavity, while depression of the ribs decreases the lateral
dimensions of the thoracic cavity.

of Respiration

that Move the Ribs

• The scalenes help increase thoracic cavity dimensions by
elevating the first and second ribs during forced inhalation.

• The ribs elevate upon contraction of the external
intercostals, thereby increasing the transverse dimensions of the thoracic
cavity during inhalation.

• Contraction of the internal intercostals depresses the
ribs, but this only occurs during forced exhalation.

• Normal exhalation requires no active muscular effort.

• A small transversus thoracis extends across the inner
surface of the thoracic cage and attaches to ribs 2–6. It helps depress the 23 ribs.

• Two posterior thorax muscles also assist with respiration.
These muscles are located deep to the trapezius and latissimus dorsi, but
superficial to the erector spinae muscles.

• The serratus posterior superior elevates ribs 2–5 during
inhalation, and the serratus posterior inferior depresses ribs 8–12 during

• In addition, some accessory muscles assist with
respiratory activities.

• The pectoralis minor, serratus anterior, and
sternocleidomastoid help with forced inhalation, while the abdominal muscles
(external and internal obliques, transversus abdominis, and rectus abdominis)
assist in active exhalation.

Boyle’s Law

• The pressure of a gas decreases if the volume of the
container increases, and vice versa.

• When the volume of the thoracic cavity increases even
slightly during inhalation, the intrapulmonary pressure decreases slightly, and
air flows into the lungs through the conducting airways.

• Air flows into the lungs from a region of higher pressure
(the atmosphere) into a region of lower pressure (the intrapulmonary region).

• When the volume of the thoracic cavity decreases during exhalation,
the intrapulmonary pressure increases and forces air out of the lungs into the

Control by Respiratory Centers of the Brain

• The trachea, bronchial tree, and lungs are innervated by
the autonomic nervous system.

• The autonomic nerve fibers that innervate the heart also
send branches to the respiratory structures.

• The involuntary, rhythmic activities that deliver and
remove respiratory gases are regulated in the brainstem.

• Regulatory respiratory centers are located within the
reticular formation through both the medulla oblongata and pons.

Aging and
the Respiratory System

• Becomes less efficient with age due to several structural

• Decrease in elastic connective tissue in the lungs and the
thoracic cavity wall.

• Loss of elasticity reduces the amount of gas that can be
exchanged with each breath and results in a decrease in the ventilation rate.

• Emphysema may cause a loss of alveoli or their

• Reduced capacity for gas exchange can cause an older
person to become short of breath upon exertion.

• Carbon, dust, and pollution material gradually accumulate
in our lymph nodes and lungs.

Regulation during Exercise

Pulmonary Ventilation

– Commonly referred to as breathing    

– Process of moving air in and out of the lungs  

– Nasal breathing: warms, humidifies, and filters the air we

– Pleural sacs suspend the lungs from the thorax and contain
fluid to prevent friction against the thoracic cage.

Bronchial tree

Intercostal muscles

The composition of
inspired and expired air


Inspired air %

Expired air %




Carbon dioxide



Nitrogen and rare gases



Water vapour



Partial pressures of


















Carbon dioxide







Nitrogen and other inert gases







Water vapour







Total =







and Internal Respiration-Mechanism


• Inspiration

– is an active process of the diaphragm and the external
intercostal muscles.

– Air rushes in into the lungs to reduce a pressure

– Forced inspiration is further assisted by the scalene,
sternocleidomastoid, and pectoralis muscles.

• Expiration

– is a passive relaxation of the inspiratory muscles and the
lung recoils.

– increased thoracic pressure forces air out of the lungs

– Forced expiration is an active process of the internal
intercostal muscles (latissimus dorsi, quadratus lumborum & abdominals).


• Is the gas exchange in the lungs and serves two functions:

– It replenishes the blood’s oxygen supply in pulmonary

– It removes carbon dioxide from the pulmonary capillaries

• The respiratory

– Gas exchange occurs between the air in the alveoli,
through the respiratory membrane, to the red  
blood cells in the blood of the pulmonary capillaries.

• Partial Pressures
of gasses

– The individual pressures from each gas in a mixture together
create a total pressure.

– Air we breathe = 79% (N2), 21% (O2), and .03% (CO2) =

– Differences in the partial pressures of the gases in the
alveoli and the gases in the blood create a pressure gradient.

• OdžLJgen’s rate at which it diffuses from the alveoli into
the blood is referred to as the oxygen diffusion capacity.

• Untrained (45 ml/kg /min) vs trained (80 ml/kg /min) – Due
to increased cardiac output, alveolar surface area, and reduced resistance to
diffusion across the respiratory membranes.

• Large athletes (males) vs small athletes (females) – Due
to increased lung capacity, increased alveolar surface area, and increased blood
pressure from muscle pumping.

Carbon diodžide’s membrane solubility is 20 times greater
than that of oxygen, so CO2 can diffuse across the respiratory membrane much
more rapidly.

of Oxygen by the Blood

• Dissolved in the blood plasma (2%)

• Dissolved with hemoglobin of red blood cells (98%)

– Complete hemoglobin saturation at sea level is 98%.

– Many factors influence hemoglobin saturation

           • Po2

           • Decline
in pH level from increasing lactate levels allows more oxygen to be unloaded
and higher Po2 is needed to saturate the hemoglobin.

           • Increased
blood temperature allows oxygen to unload more efficiently and higher Po2 is
needed to saturate the hemoglobin.

           • Anemia
reduces the blood’s oxygen-carrying capacity.

of Carbon Dioxide in the Blood

• CO2 released from the tissues is rarely (7%) dissolved in

• CO2 combines with H2O, then loses a H+ ion to form a
bicarbonate ion (HCO3) and transports 70% of carbon dioxide back to the lungs.

– The lost H+ binds to hemoglobin which enhances oxygen

– Sodium bicarbonate as an ergogenic aid serves the same
purpose as a buffer and neutralizer of H+ preventing blood acidification.

• CO2 can also bind with the amino acids of the hemoglobin
to 10

of Pulmonary Ventilation

• Mechanisms of pulmonary ventilation

– controlled by respiratory centers of the brainstem by
sending out periodic impulses to the respiratory muscles.

– Chemoreceptors also stimulate the brain to stimulate the
respiratory centers to increase respiration to rid the body of carbon dioxide.

– Stretch receptors of the pleurae, bronchioles and alveoli
send impulses to the expiratory center to shorten inspiration.

– The motor cortex of the voluntary nervous system can
control ventilation but can also be overriden by the involuntary system.

centres of Respiration

Limitations to Performance

• Energy produced by oxidation and used by the respiratory muscles
increases from 2% to 15% during heavy exercise.

• Pulmonary Ventilation might be a limiting factor in highly
trained subjects during maximal exhaustive exercise due to a high Vo2 max.

• Airway Resistance and Gas Diffusion in the lungs do not
limit exercise in a normal healthy individual.

• Restrictive or Obstructive Air Ways can limit athletic
performance by decreasing the Po2 or increasing the Pco2.

– Asthma

– Bronchitis

– Emphysema

Regulation of Acid-Base Balance

• Chemical Buffers

– Bicarbonate, phosphates, and proteins

– Increased ventilation to decrease H+

– Accumulated H+ is removed by the kidneys and urinary

– H+ is difused throughout the body fluids and reach
equilibrium after only 5 to 10 minutes of recovery

• This is facilitated by active recovery.

Static Lung

• Total Lung Capacity

• Tidal Volume

• Inspiratory Reserve Volume

• Expiratory Reserve Volume

• Residual Lung Volume

• Forced Vital Capacity

• Inspiratory Capacity

• Functional Residual Volume

volumes and capacities

• Anatomical dead
As the exchange of gases takes place only across the walls of the
alveolar ducts and alveoli, the remaining capacity of the respiratory passage
is Anatomical dead space (150ml)

• Tidal Volume- Amount
of air passing into and out of lungs during each breath (500ml at rest)

• Inspiratory Reserve
Extra volume of air that can be inhaled into the lungs during
maximal inspiration

Expiratory Reserve
Volume –
Largest volume of air which can be expelled from the lungs during
maximal respiration

• Residual Lung
Volume –
volume of air remaining in the lungs after forced expiration

• Vital Capacity =TV+IRV+ERV

• Inspiratory
Capacity –
Amount of air that can be inspired with maximum effort

• Functional Residual
Amount of air remaining in the air passages and alveoli at the end
of the respiration.

• Alveolar
Volume of air that moves into and out of the alveoli per
minute (TV – ADS X Respiratory rate) (500-150 X 15=5.25litres/min

Disorders of Respiratory System

• URI – Upper
Respiratory Infection –
infection of nose, throat, larynx, trachea

• Pneumonia –
inflammation or infection of the lungs

• Emphysema (Chronic
Obstructive Pulmonary Disease – COPD) –
alveoli become stretched and stiff
preventing adequate exchange of oxygen and carbon dioxide

• Asthma – spasms
of bronchial tube walls causing narrowing of air passages usually due to

• Allergy –
reaction to substances that leads to slight or severe response by body.

• Influenza –
highly contagious URI

• Pleurisy –
inflammation of the pleura surrounding the l

• Bronchitis –
inflammation of the bronchi

• Lung cancer – malignant
tumors in the lungs that destroy tissue

Changes in
Respiratory System – Due To Aging

• Lung tissue becomes less elastic

• Respiratory muscles weaken

• Number of alveoli decrease

• Respirations increase

• Voice pitched higher and weaker due to changes in larynx

• Chest wall and structures become more rigid

of Respiratory System

• Rate and rhythm of respirations

• Respiratory secretions – character

• Character of cough

• Changes in skin color – pale or bluish gray

• Temperature changes

• Difficulty breathing

• Color of sputum

• Complaint of pain in chest, back, sides

• Shortness of breath

• Noisy respirations

• Sneezing

• Gasping for breath

• Anxiety


• Respiratory System structurally divided into Upper and
lower respiratory tract

• Respiratory System functionally divided into Conducting
and respiratory portion

• The human respiratory system is a series of organs
responsible for taking in oxygen and expelling carbon dioxide. The primary
organs of the respiratory system are lungs, which carry out this exchange of gases

• Breathing – Two cyclic phases – Inhalation and exhalation

• Gas exchange takes – External and Internal respiratory

• Main functions of respiratory system – Gas conditioning,
Sound production, Olfaction and Defense

• Gas exchange – It takes place in the respiratory
bronchioles, alveolar ducts and in the lungs

• Inhalation – External intercostal muscle contract and
elevate the ribs.

• As the diaphragm contracts, the rib cage is simultaneously
enlarged by the ribs being pulled upwards by the intercostal muscles

• Normal exhalation requires no active muscular effort

• The trachea, bronchial tree, and lungs are innervated by
the autonomic nervous system

• Regulatory respiratory centers are located within the
reticular formation through both the medulla oblongata and pons

• Regulatory respiratory centers are located within the
reticular formation through both the medulla oblongata and pons.

• COPD, Asthma, Bronchitis are common disorders of
respiratory tract.

• Tidal volume, vital capacity all are important for measurement
of total lung capacity


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