COMPARATIVE ACCOUNT OF RESPIRATORY SYSTEM WITH … · 2020-03-28 · 1. Lungs are comparitvely more...
Transcript of COMPARATIVE ACCOUNT OF RESPIRATORY SYSTEM WITH … · 2020-03-28 · 1. Lungs are comparitvely more...
COMPARATIVE ACCOUNT OF RESPIRATORY SYSTEM WITH SPECIAL
REFERENCE TO THE PHARYNX
Respiration is the process of exchange of gases (O2 and CO2). The oxygen is taken inside the
body from the environment for oxidation of food to release energy & CO2 so produced is
expelled out. The respiratory organs in vertebrates are either the gills or the lungs which are
associated with the pharynx.
The basic necessities of any respiratory organ are
1. The respiratory organs must be thin walled so that there is easy diffusion of gases
2. It must be richly supplied with blood enable exchange of gases
3. It should have large area for contraction and expansion.
Respiratory organs
1. Gills : Fish, larval amphibians, adult urodeles
2. Swim bladder: Fishes
3. Lungs: Tetrapods (amphibian, reptilia, birds &mammals)
I. GILLS
In fishes, gills are the main respiratory organs. In amphibian’s larval forms (tadpole) and in the
adult urodels gills are the respiratory organs.
Development of gills
a) In the embryo, the pharynx develops paired pouches due to evagination or pushing out.
At the same time skin develop grooves due to invagination or pughing in when the pouch
and the groove meet and the membrane between the two disintegrates, a slit develops to
form gill slit
b) The gill cleft or slit contains gills which are present in a gill chamber
c) Each gill chamber has an internal branchial aperture opening to pharynx
d) An external branchial aperture opens to external
e) The gill chambers are separated by inter branchial septa and supported by gill rays
f) Each half of the gill filament is called Demibranch.
g) The demibranch on either side of interbranchial septum, gillrays, connective tissue and
associated blood vessels with nerves form a holobranch.
h) The demibranch at the anterior end is called pre-trematic demibranch and at the
posterior end is called post trematic demibranch.
GILLS IN FISHES: are internal and vary in number depending on the classes they belong to.
Note: Operculum is a bony flap like covering that is seen over the gill slits on either sides in
bony fishes; they develop from the hyoid arch an extends backwards or posterior, covering the
gill slits
Difference between bony and cartilaginous fishes
Cartilaginous fishes
(Elasmobranches or Chondrichthyes)
Bony fishes
(Teleosts/ Osteichthyes)
There are five pairs of gill slits There are four pairs of gill slits
There are a pairs of spiracle in front of the
hyomandibular arch
Spiracles are absent
Operculum is absent Operculum is present
Gills open to the exterior by inter branchial aperture Gills open to the opercular chamber
opercular chamber is absent opercular chamber is present
They have 1 demibranch & 5 Holobranches They are 4 holobranch, the demibranch
of the first gill is lost
GILLS IN AMPHIBIANS: The larval forms called tadpoles are purely aquatic and they need to
utilize oxygen in the water. This can be done only with the help of gills. Initially three pairs of
external gills (gills that are constantly bathed in water) will be developed which will be replaced
by internal gills as the development proceeds. In most of the amphibians these internal gills will
be replaced by lungs during metamorphosis. Only in Urodeles like Salamanders and Necturus, 3
pairs of external gills persist throughout the life.
II. SWIM BLADDER/AIR BLADDER
Swim bladders or air bladders are paired or unpaired structures arising from the pharynx or
oesophagus of bony fishes. The air bladder arises as an outgrowth of the pharynx on either side,
initially lateral in position then becomes dorsal. It lies below vertebral column and outside
coelom.
Connection between between the pharynx and airbladder is called pneumatic duct. Swim
bladder serves both as respiratory and hydrostatic organ. In lung fishes the Swim bladders
resembles the lungs. They arise from the ventral part of the pharynx. The lining of air bladder
shows several air sacs. Arteries arising from 6th embryonic arch supply the airbladder.
Oxygenated blood is returned to the left atrium of heart.
When the fish gulps in air, it enters inside through mouth and pharynx, Oesopharyngeal pump
forces air into pneumatic duct. There is exchange of gases inside airbladder. When air bladder is
compressed, gas exchange & CO2 is expelled through the mouth as bubbles. In lungfishes like
Protopterus and Lepidosiren, swim bladder is a better respiratory organ that makes respiration
more effective eventhough they have lesser number of demibranches.
III. LUNGS
All air breathing organisms possess lungs. From amphibians to mammals, all terrestrial
organisms posses lungs that arise from pharynx.
Formation of lungs
1. Lungs develop from the floor of pharynx at its posterior end as
a single small bud called lung bud through single evagination.
2. The lung bud slightly elongates & bifurcates into two
3. The opening of lung bud into the pharynx develops a small slit
& form the glottis. The part after glottis forms the larynx
(voice box)
5. The elongated part of the lungs before bifurcation forms
Trachea (wind pipe)
6. The bifurcated part becomes the bronchi
7. The ends of bifurcated parts of the lung buds expand to form
lungs.
8. The lungs push backwards & come to lie on either side of the
heart. Lungs get surrounded by coelomic epithelium
LARYNX
Larynx is the part between glottis and upper end of trachea, well developed in tetrapods
a. Larynx in Amphibia
a. In amphibians like anurans there is a laryngo-tracheal chamber for production of sound
(urodeles and apodans do no not produce sound)
b. Laryngo-tracheal chamber has three cartilaginous structures to keep it stretched-one ring
like cricoid cartilage and two semicircular arytenoids cartilages
b. Larynx in Reptiles
Larynx in reptiles is similar as in frog. But there is a well developed hyoid cartilage to hold
larynx in position
c. Larynx in Birds
In birds larynx is simple and there is another organ for sound production called Syrinx
d. Larynx in Mammals
In mammals Larynx is Highly developed with 3 cartilages
I. Thyrenoid/ thyroid cartilage which forms a half ring like structure at the anterior end of
larynx
II. Dorsal to thyroid cartilage is the arytenoids
III. Below arytenoids are the crinoids, followed by trachea.
Anterior to glottis is an epiglottis which is a fold of mucous membrane of pharynx supported
by an internal cartilage. The epiglottis kept erect while breathing, but while feeding it is pulled
down to closes the glottis. A pair of vocal cords is found between thyroid & arytenoids
cartilages to produce sound.
TRACHEA
Lungs in amphibians
Amphibian lungs are not very efficient (hence they rely on cutaneous respiration).
Amphibian lungs vary in different orders,
Urodela Anura (eg: frog)
1.Lungs are less functional, when compared to gills
1. Lungs are comparitvely more functional, no gills
2. Lungs of Siren is as long as body cavity 3. Lungs of Necturus is long and poorly vascularised
2. Lungs are not long. They are thin walled sac like structures covered by peritoneum. Internal linings of lungs are folded to increase the surface area for exchange of gases 3. The space inside is divided into smaller areas called alveoli, which are highly vascularised, Inner lining has mucous glands.