Mrs. Ofelia Solano Saludar
Department of Natural Sciences
University of St. La Salle
Bacolod City
1. Compare and contrast the advantages/
disadvantages of counter current and concurrent
types of ventilation on vertebrate respiration.
2. Describe the functional anatomy of gills, lungs.
3. List the requirements that a fish must undergo to
become a terrestrial vertebrate.
4. Discuss how the swim bladder is structurally and
functionally related to the lungs.
5. Discuss the phylogeny and attendant modifications
of the respiratory tract of the following groups:
a. fishes
b. amphibians
c. reptiles
d. birds
e. mammals
- the process of obtaining oxygen
from the external environment & eliminating CO2.
Respiratory System Principles
1. Movement of an O2-containing medium so it
contacts a moist membrane overlying blood
vessels.
2. Diffusion of O2 from the medium into the blood.
3. Transport of O2 to the tissues and cells of the
body.
4. Diffusion of O2 from the blood into cells.
5. CO2 follows a reverse path.
1. External respiration - O2 and CO2 exchanged
between the external environment & the body
cells by diffusion; takes place via highly
vascular membranes with thin, moist epithelia
2. Internal respiration - gas exchange between
blood & cells; cells use oxygen for ATP
production & produce CO2 as waste product
 Ventilation – bringing gas in contact with
respiratory exchange surfaces, e.g. water
through gills, or air in & out of lungs of
vertebrates, tracheoles of insects
 Afferent & efferent blood vessels conduct
blood to and from sites of respiratory
exchange

Primary organs in adult vertebrates are external
& internal gills, swim bladders or lungs, skin, &
the buccopharyngeal mucosa

Less common
respiratory
devices include
filamentous
outgrowths of
the posterior
trunk & thigh
(African hairy
frog), lining of
the cloaca, & lining of esophagus
 Respiration
through the skin
can take place in
air, water, or
both
 Most important
among
amphibians
(especially the
family
Plethodontidae)




Outgrowths from the
external surface of 1
or more gill arches
Filamentous
extensions of internal
gills that project
through gill slits
Gill slits & external
gills occur in
amphibian larvae &
adult urodeles
Amniote embryos
have gill slits with no
traces of gills
– wall of pharynx is pierced by
typically 6 gill slits between skeletal gill
arches; gill pouch is the passage between
external & internal slits; the tissue between
gill pouches is the gill bar; bars bear
internal gill with filaments.
Mouth
Gill arch
Pharynx
Gill filaments
Gill pouch
 May be external or internal
 External in dipnoans, a few
actinopterygians, amphibians
 Filamentous internal gills in a few teleosts
and larval elasmobranchs
 Maintain salt homeostasis
 Excretion of nitrogenous wastes and CO2
 Little or no septum because operculum
covers and protects gills
 Ventilation is similar to shark
Mouth
Operculum
Gill arch
Gill filaments
Gill structure
• Gill septae or
interbranchial
septum is between
gills
• Gill bar extends to
body surface for
more support
• Gill filaments have
rakers: inner
surface of gills
which keeps food
out of gills
• Holobranch – gill
filaments on both
sides of gill
• Hemibranch – gill
filaments on one
side of gill
• Pseudobranch –
false gill, faces
into spiracle and
monitors oxygen
requirements to
eye

In fishes, the arches are supplied with
respiratory branchial muscles & aortic blood
vessels

In amniotes, the tympanic cavity & auditory
tube connecting it with the pharynx develop as
an outgrowth from the 1st gill pouch.

The external auditory meatus is a depression in
the position of the 1st gill slit.

The entodermal lining of the gill pouches
persists as tonsils, thymus, parathyroids &
epithelial bodies

The thyroid gland persists as an evagination of
the pharyngeal floor between the 2nd gill arches.
 Extant jawed fishes- lead to blind
olfactory sacs
 Dipnoans & tetrapods- connected
with oropharyngeal cavity or pharynx
via nasal canals; respiratory use only
in tetrapods
:
 Opens further caudad if secondary
palate is present
AGNATHANS:
• 5-15 pouched gills;
branchial basket
support
• External & internal
branchial pores
• Pulsations of branchial
muscles move water in
and out of same
openings, as mouth is
attached to prey
• Pouches connected to
pharynx by afferent
branchial ducts & to
exterior by efferent
branchial ducts
CHONDRICHTHYANS
 5 ‘naked’ gill slits
with apertures
protected by flaplike
valve
 Septae support
septal gills which
look like a set of
stacked plates
 Spiracle is modified
first gill pouch for
water intake
 Posterior wall of last
(5th) chamber has no
demibranch.
TELEOSTS:





5 gill slits
Operculum projects
backward over gill
chambers
Interbranchial septa
are very short or
absent
Most do not have
spiracle
A branchiostegal
membrane is attached
to the operculum,
supported by gular
bones or
branchiostegal rays.
 Pneumatics sacs arising as paired or
unpaired endodermal outpocketing of
embryonic foregut.
 Similarities between swim bladders & lungs
indicate they are homologous organs.
 Swim bladder dorsal, lungs ventral
 Serve primarily as a hydrostatic organ
(regulates a fish's specific gravity)
 Vertebrates without swim bladders or lungs
include cyclostomes, cartilaginous fish, and
a few teleosts.
 Have a pneumatic duct that connects to the
esophagus.
 The duct remains open (physostomous) in
bowfins and lungfish, but closes off
(physoclistous) in most teleosts.
 Ventilation: from mouth to pneumatic
duct to swim bladder
 Gain gas by way of a 'red body' (red gland)
 Gas is resorbed via the oval body on
posterior part of bladder via rete mirabile,
a network of blood vessels
 Countercurrent blood flow
Swim bladders also play important roles in:
Respiration - the swim bladder of lungfish has a number
subdivisions or septa (to increase surface area); O2 and
CO2 is exchanged between the bladder & the blood
Sound production - muscles attached to the swim
bladder contract to move air between 'sub-chambers' of
the bladder. The resulting vibration creates sound in fish
such as croakers, grunters, & midshipman fish.
Hearing - some fresh
water teleosts (catfish,
goldfish, carp) 'hear' by
way of pressure waves
transmitted via the swim
bladder and small bones
called Weberian ossicles

Gills are efficient in water but on land, gills will
collapse and will lose water quickly. Terrestrial
organisms had to evolve respiratory surfaces within
the body cavity to reduce water loss.

A “lung fish” has LUNGS for adaptations to living on
oxygen-poor water or to spending time exposed to air.
Amphibians:
 Lungs are 2 small,
simple sacs that
do not provide a
large surface
 Occupy the
pleuroperitoneal
cavity
 Internal lining may
be smooth or have
simple
sacculations or
pockets
In Urodeles, lungs are often of minor
importance; respiration is often through
external gills and skin
 In Anurans, the larynx is the cartilaginous entry
into trachea; the opening of larynx is the glottis
 Internal nares are functional for first time in
evolutionary history
 Air is exchanged via positive-pressure
ventilation; involves gulping (pulse pump)

Amphibians force air into their lungs by creating a greater-thanatmospheric pressure (positive pressure) in the air outside their
lungs. They do this by filling their buccal cavity with air, closing
their mouth and nostrils, and then elevating the floor of their oral
cavity. This pushes air into their lungs in the same way that a
pressurized tank of air is used to fill balloons. This is called positive
pressure breathing; in humans, it would be analogous to forcing air
into a victim’s lungs by performing mouth-to-mouth resuscitation.
Reptiles

Similar to amphibians in anatomy

Air is exchanged via positive- pressure ventilation;
suction effect

Inspiration involves
creating negative
pressure inside
chest cavity via
intercostal and
abdominal muscles

Expiration is passive

Each lung occupies a pleural cavity; a fibrous
oblique septa separate pleural cavities from the rest
of the coelom

Lizards, crocodilians, & turtles – highly
compartmentalized

Some turtles supplement lung breathing with gas
exchange across moist epithelial surfaces in their
mouth and anus.
Avians
 Modified
from those
of reptiles
 Trachea
delivers air
to bronchi
 The primary
bronchi are
divided into:
ventrobronchi, dorsobronchi, and thousands
of parabronchi in between

Highly vascularized: capillaries are open ended in the
walls of parabronchi; form a honeycomb appearance

Inhaled air flows nonstop through the lungs and into
air sacs, returns to the lungs via recurrent bronchi,
flows through open-ended capillaries, and then
vented.
Air sacs: 2 abdominal; 2 posterior thoracic; 2
anterior thoracic; 2 cervical; 1 interclavicular
FUNCTIONS OF AIR SACS
• Air sacs act as bellows to allow continuous
ventilation
• Unidirectional air flow through lungs and air
sacs result to extremely efficient ventilation
• High vascularity allows for efficient diffusion
between air sacs and blood capillaries
• Penetrate some bones making them lighter
• Thermoregulatory
• Buoyancy in water fowl
 Inhaled air flows through lungs & into
air sacs which extend into viscera and
hollow
bones
 No deadend
passages
of air
ducts
(crosscurrent)
 Syrinx- vocal apparatus in interclavicular air
sac region
 Furcula- flight muscles acts as a pressure
pump that allows expansion and contraction
of air air sacs during flight
Mammals:

Multichambered &
usually divided into
lobes; highly spongy

Diaphragm separates
pleural cavity;
mediastinum
separates each
pleural cavity

Bidirectional air flow:
Trachea <-> 10
bronchi <-> 20
bronchi <-> 30 bronchi
<-> bronchioles <->
alveoli
Air is exchanged via negative pressure
ventilation, with pressures changing due to
contraction & relaxation of diaphragm &
intercostal muscles
 Deep-seas divers: some
elephant seals can dive for
1500 m and stay for 2 hours!

Weddel Seal routinely
plunges 200-500 m for 20 –
60 min!

Storage of oxygen in blood
and muscle: 2x as much the
volume of blood compared
to humans

Most oxygen in blood (70%)
vs lungs (5%); in humans:
blood (51%) and lungs
(36%)
 Tetrapods besides
mammals - 2 pair of
cartilages:
arytenoid & cricoid
 Mammals - paired
arytenoids + cricoid
+ thyroid + several other small cartilages
including the epiglottis (closes glottis when
swallowing)
 Amphibians, some lizards, & most mammals also have vocal cords stretched across the
laryngeal chamber
Stalk of bifurcated
lung outgrowth;
supported by
cartilaginous rings
Leads to bronchi
(forms the bird syrinx
at that point)
Usually about as long
as a vertebrates neck
(except in a few birds
such as cranes)