The respiratory system has several functions including providing oxygen for cellular respiration and removing carbon dioxide. It involves gas exchange that occurs in the alveoli between inhaled air and blood. The major structures include the nasal cavity, pharynx, larynx, trachea, lungs, bronchi, bronchioles and alveoli. During inhalation, intercostal muscles and the diaphragm expand the chest cavity to create lower pressure and allow air intake. Exhalation is passive as respiratory muscles relax and pressure decreases within the chest to expel air. The pleura and elasticity of the lungs allow for adequate expansion and contraction during breathing.

1. The Respiratory System
ATS Unit 6

2. Learning Goals
• Describe the functions of the respiratory
system.
• Identify the major structures of the
respiratory system and their function.
• Discuss the physiological process of external
respiration.

3. Functions of the Respiratory System
1. Provide oxygen for cellular respiration.
2. Dispose of Carbon Dioxide, a waste product
of cellular respiration.
3. Production of sounds.

4. External Respiration
• This is the gas exchange that occurs in the
alveoli of the lungs, between inhales air and
the blood in the alveolar capillaries.

5. Structures of the Respiratory System
• From superior to inferior:
– Nasal Cavity
– Pharynx
– Larynx
– Trachea
– Lungs and Pleura
– Bronchi and Bronchioles
– Alveoli
– Diaphragm

6. The Nasal Cavity
• Opening are called nostrils or
nares.
– Divided by a septum.
– Further divided into cavities
called turbinate's which creates
three narrow passages ways in
the cavity (crates movement in
inhaled air).
– The cavity is lined with
epithelium that is ciliated and
produces mucous (to clean and
moisten inhaled air).

7. Sinuses and the Sense of Smell
• Sinuses are cavities located in the
various bones of the skull with
outlets into the nasal cavity.
– These are also lined with mucous
membranes.
– They help to make the skill lighter.
– They give resonance to the voice.
The olfactory nerves are in the
superior surfaces of the nasal cavity
and lead to the olfactory nerve in the
brain. We will talk more on this later
(unit 8).

8. The Pharynx
• This is commonly called the
throat and is a common
passage for both air and food.
– Three portions: Nasopharynx,
Oropharynx, Laryngopharynx
– Connects to the Eustachian
tubes which drain the inner ear.
– Extends down to the epiglottis.

9. The Epiglottis
• This is a flap made of cartilage found behind
the tongue at the bottom of the
laryngopharynx.
– At rest, it stands upright to allow air to pass into
the larynx.
– It closes during swallowing to prevent food from
entering the lungs.

10. The Larynx
• AKA the Voice Box
– This a made of several plates
for cords of fibrocartilage.
– The opening in called the
glottis (epiglottis means?)
– As air leaves the lungs,
muscles tighten the cords to
allow vibration to occur that
create sound.
– Sounds are refined by
movements in the mouth,
tongue and lips.

11. The Trachea
• This tube extends from the Larynx to the point
where it divides into the Bronchi.
– It is constructed of membranes supported by
string but flexible hyaline cartilage rings. This
makes it very hard to collapse.
– It runs in front of the esophagus.
– Continues to be lined by the ciliated, mucous
producing epithelium found in other parts of the
respiratory tract.

12. The Bronchi and Bronchioles
• These tubes, very similar in structure to the
trachea, extend first to the left and right
Bronchi and then into increasingly smaller
branches into all lobes of the lungs.

13. Alveoli
• At the end of each small bronchiole,
there is a collection of alveoli.
– An Alveolus is a small sack made of thin
epithelium, surrounded by capillaries.
– On inhale, they fill with air that can then
be diffused across the membrane of the
alveolar sack and into the capillaries full
of deoxygenate blood from the heart.
– A substance in the alveoli called
surfactant keeps them from collapsing on
exhale.

14. The Lungs and Pleura
• All od the bronchi, bronchioles and alveoli are
housed in two soft organs called the lungs.
– The left has two lobes and the right has three.
– They are housed in the thorax, above the
diaphragm and are separated from the heart by
the membranes of the mediastinum.
– They have their own two layer membrane (with
lubricating fluid in-between) called the pleura.

15. The Diaphragm
• This is a dome shaped muscle that sits below
the lungs in the thorax.
– It divides the thorax from the abdominal contents.
– It is necessary for the physical process of
breathing.
– It is stimulated by the phrenic nerves to contract.
– It is a skeletal muscle but works both voluntarily
and involuntarily.

16. The Mechanics of Breathing: Inhale
(Inspiration)
• This is the active part of the cycle.
– The intercostal (rib muscles) pull the rib cage up
and out. The diaphragm expands down
(contracting).
– This expansion of the chest cavity creates lower
pressure inside than out, causing air to rush in.
– Outwardly, we see the chest rise and expand, and
the abdomen distend slightly as the contents are
pushed down by the diaphragm.

17. Mechanics of Breathing: Exhale
(Expiration)
• This is the passive part of the cycle.
– All respiratory muscles relax to original shape and
position. Rib cage descends and collapses slightly.
– As this occurs, the pressure in the outside of the
body becomes lower than inside the chest cavity
and air is forced out.
– Outwardly, the shoulders and chest descend, the
abdomen flattens.

18. Things that keep you breathing…
• The Pleura:
– Without the air tight chest cavity created by the
pleura around the lungs, expansion would not be
possible, because air could pass freely through the
chest wall.
• The Elasticity of the Lungs
– They need to be able to expand and contract as they
fill and empty.
– In some diseases, the lungs become scarred and
fibrotic and cannot expand and collapse adequately.