It is a biological system consisting of specific organs
and structures used for the process of respiration in
WHAT IS RESPIRATORY SYSTEM?
Gas exchange: Oxygen enters blood and carbon
Regulation of blood pH: Altered by changing blood
carbon dioxide levels
Voice production: Movement of air past vocal folds
makes sound and speech.
Olfaction: Smell occurs when airborne molecules are
drawn into nasal cavity.
Protection: Against microorganisms by preventing
entry and removing them from respiratory surfaces.
RESPIRATORY SYSTEM FUNCTIONS
Respiratory system does this through breathing.
When we breathe, we inhale oxygen and exhale
carbon dioxide. This exchange of gases is the
respiratory system’s means of getting oxygen to the
HOW DOES IT WORK?
Endoderm forms the respiratory system, having a
sheet of approximately 500-1000 cells.
Phases of Lung Development- growth and
Mechanism of respiration
Chordates have one of two basic structures for
Gills – for aquatic chordates
Example: tunicates, fish and amphibians
Lungs - for terrestrial chordates
Examples: adult amphibians, reptiles, birds, and mammals
1.) Aquatic Gills
through the mouth
then over the gills
where oxygen is
and water are then
Increase the surface area
Containing blood vessels covered by a thin epithelial
Organized into a series of plates
internal (as in crabs and fish) or
external to the body (as in some amphibians).
2. ) Vertebrate lungs
As you move from amphibians to mammals the
surface area of the lungs increases
Insures a greater amount of gas exchange (or a two way
flow of air).
Birds, by contrast have lungs and air sacs which
have only a one-way flow of air.
This allows for them to have constant contact with fresh
This adaptation enables them to fly at high altitudes
where there is less oxygen.
Salamander Lizard PigeonPrimate
Nostrils, mouth, and
Figure 33–10: Vertebrate Lungs
Amphibians, Humans (also)
-ancestral form of respiration
-sometimes used External cutaneous respiration
-Use their outer surfaces
-Gas exchange occurs at capillaries located
throughout the body
Pharynx Trachea Bronchi
air to the
Movement of Oxygen and Carbon Dioxide In and
Out of the Respiratory System
WHY DO ANIMALS BREATHE?
mediate gas exchange
located at the side of the head
made up of gill filaments , feather structures that provide a
large surface for gas exchange
Adult fishes have a pair of gills. Each gills is covered
by a bony lid. A fish draws in water by closing the lid over
its gills and opening its mouth. When the fish closes its
mouth and opens the gill lid, the water is forced out and
over the respiratory surfaces of the gill filaments.
Gill filaments – the site of gas exchange
(Each gill filament consists of an upper and lower surface
covered with minute ridges known as lamellae.)
Gill rakers – appendages along the front edge of the gill
Gill arches – support the gills
Swim bladder – gas filled chamber that allow the bony fish
to remain floating in the water
Water enters the gill chamber through the fish’s mouth and
exits through gill openings under the operculum. Blood
flowing through the gill filaments absorbs oxygen from the
Some species of bony fishes can absorb considerable
amounts of oxygen through their skin.
Usually have 5 gill slits
Operculum projects backward over gill chambers
Interbranchial septa are very short or absent
Lamellae are made of extremely thin membranes (1 cell
thick) and are primary sites of gas exchange.
Water flows across the gill filaments and oxygen is
removed and passes into the blood by diffusion.
To increase the efficiency of oxygen uptake a
countercurrent method is used; blood flows through the
lamellae in a direction opposite to the water flow through
the gill filaments. Countercurrent flow ensures a steady
The anatomical structure of the lungs is less
complex in reptiles than in mammals, with
reptiles lacking the very extensive airway
tree structure found in mammalian lungs. Gas
exchange in reptiles still occurs
in alveoli however, reptiles do not possess
Thus, breathing occurs via a change in the
volume of the body cavity which is
controlled by contraction of intercostal
muscles in all reptiles except turtles. In
turtles, contraction of specific pairs of flank
muscles governs inspiration or expiration.
To survive on land, the reptiles had to develop a skin relatively impermeable to water, so as
to prevent desiccation, and hence not well suited for respiration. The most complex
reptilian lungs are found in sea turtles such as Chelonia mydas, the green turtle.
Crocodiles and alligators have a specialized muscle attached to the posterior surface of
the liver; the anterior surface of the liver in turn is attached to the posterior surface of
The adoption of a rigid shell by turtles and tortoises necessitated the development of
highly specialized skeletal muscles to inflate the lungs. In the tortoise Testudo graeca,
lung ventilation is achieved by changing the volume of the body cavity.
The breathing patterns of most reptiles are not regular, usually consisting of a series of
active inspirations and expirations followed by relatively long pauses. The metabolic rate
of most reptiles is one-fifth to one-tenth that of birds or mammals, and constant lung
ventilation is unnecessary in most reptiles.
PARTS and FUNCTIONS
Larynx – also known as “voice box”. This is supported by the hyoid cartilage
HYOID CARTILAGE – a flat body covered by the muscles at the floor of the
Arytenoids – a pair of valve like cartilage forming the dorsal roof of pharynx
and sides of glottis
Lungs – a pair of thin-walled sacs located at the antero-lateral region of the
Cricoid – a ring like cartilage surrounding the arytenoids.
Vocal cords – the sound producing apparatus inside the larynx
Alveoli – found at the inner wall of the lungs which divides the lungs into
Pleural membrane – shiny thin membrane that covers the outer surfaces of
Glottis – opening of the larynx.
Unlike birds and mammals, amphibians are cold
They do not use up any energy for keeping their
bodies at a constant temperature.
Respiration through lungs is called PULMONARY
This respiration occurs only when the need of Oxygen
is more during swimming and jumping
Alveoli are present. Air enters into the alveoli through
the external and internal nares, buccopharyngeal
cavity, glottis, laryngotrachial chamber, and bronchi.
DIFFERENCE BETWEEN AMPHIBIAN
LUNGS AND HUMAN LUNGS
Alveoli increases the amount of surface
that oxygen can enter our bodies
Since amphibians don’t need much
oxygen as humans, they have less
HAS A DIAPHRAGM
It causes the air to rush in and out of the
They have to force air into their lungs by
moving their mouth as we do while
Respiration through the skin is called CUTANEOUS
It occurs in hibernation and in water
The skin of amphibians are very thin and is rich with
The water carries oxygen which diffuses into the
capillaries and the carbon dioxide in the blood
• Thermoregulation (maintaining
normal body temp.
• Larynx – is not used to make sound
• Syrinx – serve as voice box
• Air Sacs - Depending upon the
species, the bird has seven or nine
The air sacs include:
Two posterior thoracic
Two anterior thoracic
Two cervical (these are not
present in some species)
The air sacs of birds extend into the humerus (the bone
between the shoulder and elbow), the femur (the thigh
bone), the vertebrae and even the skull.
The gas volume of the bird lung <
gas volume of the mammal lung.
Lung is connected to
voluminous air sacs by a series of
tubes, making the total volume of
the respiratory system about twice
that of mammals of comparable
Birds do not have a diaphragm.
air is moved in and out of the
respiratory system through pressure
changes in the air sacs.
Aspiration into the air sacs is
produced by expansion of the chest
and abdominal cavity.
Expiration is caused by compression
of the air sacs by skeletal muscle, this
causes the sternum to be pushed
The lungs of birds do not inflate and
deflate but rather retain a constant
exchange of oxygen and carbon
dioxide occurs in microscopic sacs in
the lungs, called 'alveoli.' In the avian
lung, the gas exchange occurs in the
walls of microscopic tubules, called
The air sacs permit a unidirectional flow of air
through the lungs.
Unidirectional flow means that air moving
through bird lungs is largely 'fresh' air & has a
higher oxygen content. In contrast, air flow is
'bidirectional' in mammals, moving back and
forth into and out of the lungs.
As a result, air coming into a mammal's lungs
is mixed with 'old' air & this 'mixed air' has
less oxygen. So, in bird lungs, more oxygen is
available to diffuse into the blood
Respiratory cycle of a bird
The air does not go directly to the lung, but
instead travels to the caudal (posterior) air
sacs. A small amount of air will pass
through the caudal air sacs to the lung.
the air is moved from the posterior air
sacs through the ventrobronchi and
dorsobronchi into the lungs. The bronchi
continue to divide into smaller diameter
air capillaries. Blood capillaries flow
through the air capillaries and this is
where the oxygen and carbon dioxide
When the bird inspires the second time, the air
moves to the cranial air sacs.
On the second expiration, the air moves out of
the cranial air sacs, through the syrinx into the
trachea, through the larynx, and finally through
the nasal cavity and out of the nostrils.
Bird-like respiratory systems in dinosaurs -- A recent
analysis showing the presence of a very bird-like
pulmonary, or lung, system in predatory dinosaurs
provides more evidence of an evolutionary link
between dinosaurs and birds.
The mammalian respiratory system equilibrates air to the body,
protects against foreign materials, and allows for gas exchange.
In mammals, pulmonary ventilation occurs via inhalation
when air enters the body through the nasal cavity.
The chief organ in mammalian
respiration is the lungs.
Inhalation happens when the rib cage opens up and the diaphragm
flattens and moves downward. The lungs can then expand into the
larger space that causes the air pressure inside them to decrease,
and the drop in air pressure inside the lung makes the outside air
Exhalation is the opposite process. The diaphragm and the rib
muscles relax to their neutral state that causes the lungs to
contract. The squashing of the lungs increases their air pressure
and forces the air to flow out.
Horses are obligate nasal breathers, which means that they
must breathe through their noses.
It is thought that this modification allows horses
to graze with their heads down while separate
nasal passages breath in air and sniff for
Marine mammals breathe oxygen with lungs just like their terrestrial
brethren, but with a few differences. First of all, to prevent water from
getting into their airway they have adapted muscles or cartilaginous
flaps to seal their tracheas when under the water. Additionally, they
exchange up to 90% of their gases in a single breath, which helps them
gather as much oxygen as possible.
Lastly, it can be dangerous for diving
mammals to have air in their lungs when
they dive to great depths.