The document compares the respiratory systems of various vertebrates including fish, amphibians, reptiles, birds, and mammals. It describes the key features of respiration in fish as using gills for oxygen exchange with water. In amphibians like frogs, the respiratory system includes lungs that are sac-like with inner walls containing folds to increase surface area. The document outlines the evolution of lungs from swim bladders in fish and details features of respiration in representative species like how dogs fish use nine gill hemibranches for respiration underwater.

1. Comparative Anatomy of
Respiratory system
with special reference to
Scoliodon, Rana, Varanus, Columba and Lepus

2. ü The development of the respiratory organs in vertebrates is closely
related to the primitive pharynx, since the gills of aquatic
vertebrates and the lungs of terrestrial vertebrates and aquatic
mammals have pharyngeal embryology origin

3. ü Respiration is the process of obtaining oxygen from the external
environment & eliminating CO2.
ü Acquisition of molecular oxygen (O2) from the external media
(water and air) and the discharge of carbon dioxide (CO2) into
the same milieu is the primary role of respiration
ü External respiration - oxygen and carbon dioxide exchanged
between the external environment & the body cells
ü Internal respiration - cells use oxygen for ATP production (&
produce carbon dioxide in the process)
Water/ Air
O2
CO2
CO2
O2
Respiratory organ

4. ü Vertebrates have developed a variety of respiratory surfaces
that all increase the surface area for exchange, thus allowing for
larger bodies.
ü A respiratory surface is covered with thin, moist epithelial cells
that allow oxygen and carbon dioxide to exchange.
ü Those gases can only cross cell membranes when they are dissolved in
water or an aqueous solution, thus respiratory surfaces must be
moist.
Characteristic of respiratory organ

5. The system that has evolved in each species depends on the
environmental conditions, on body build and size, on animal’s
patterns of movement and on its energy consumption

6. Respiration in Fish

7. Organ present for respiration in fish
1) Gills 2) Air/ swim bladder
Only present in crossoptergii
and lung fishes (Assessory
respiratory organ)
A) Internal gills
All fish
B) External Gills
Larvae of lung fish
Polypterus
Lepidosiren

8. ü Gills are respiratory organ found in many aquatic organisms
that extracts dissolved oxygen from water and excretes
carbon dioxide.
ü On the basis of location gills are of two types:
1) Internal gills
2) External gills
Gills

9. ü Characteristic of fishes
ü Located in the gills slits and attached to visceral arches
1) Internal gills or true gills
ü Gills usually consist of thin filaments of tissue, branches, or
slender, tufted processes that have a highly folded surface to
increase surface area.
ü A high surface area is crucial to the gas exchange of aquatic
organisms, as water contains only a small fraction of the dissolved
oxygen that air does.
Structure

10. ü The gills are multifunctional organs that are responsible for the gas
exchange (respiration) but also for the osmoregulation, acid-base
regulation, and excretion of nitrogenous waste

11. Structure of true gills

14. ü Gills –finally divided gill filament and lamellae
ü Provide very large surface area for gas exchange

17. ü Each true gill is supported by a gill arch/gill cleft – a bony
structure that is oriented vertically on the side of a fish, just behind its
head.
ü The gill arch provides the support to hold a number of comb-
like structures called gill filaments.
ü Gill filaments extend out horizontally from the gill arches.
ü Each gill filament also called primary lamellae and the primary
lamellae branch out into tiny secondary lamellae.
ü The secondary lamellae, which are extremely numerous, are the site
of gaseous exchange and form a fine sieve which ensures that all
the water comes into close contact with the blood
ü The secondary lamellae run parallel to the flow of the water and
absorb oxygen from the water into the fish’s body.

18. Gills in elasmobranch and bony fishes
Gills of elasmobranch (eg. Dog fish ) are general in structure .
Gills of bony fishes are also basically similar but show the following
differences
1) Operculum: bony flap or gill cover arises from the hyoid arch covers
the gills, which opens by a Single slit like cresecent external gill
opening
2) Interbranchial septm: The median septum is developed in
elasmobranch and reduced in teleost
3) Spiracles : In elasmobranch and ganoids the first gill slit, between
mandibular and hyoid arches, bears a reduced pseudobranch and
opens to outside through small opening , spiracle. In chimaras and
lung fish, teleost, spiracle become either closed or lost.
4) Number : 5-7 pairs in cartilaginous and 4 pairs in bony fishes

20. ü A single row of lamellae on one side of branchial septum forms only
half the gill, called a demibranch or hemibranch.
ü A septum with two attached elsmobranchs comprise a complete gill
are holobranch.

21. Anatomy of respiratory system
in Scoliodon

22. ü Respiration is aquatic
ü Breathe by gills borne in a series of gill-pouches on either lateral side of the
pharynx
ü Water enters the mouth and after passing through the buccal cavity,
pharynx, gill- pouches bearing gill-lamallae, goes out through the external
gill-slits after bathing the gills
ü Five pairs of gill- pouches bearing gills, arranged in a series behind the hyoid
arch in the lateral walls of the pharynx.
ü In Dogfish (Scoliodon), the hyoid arch bears only a hemibranch on its
posterior surface, the first four branchial arches has holobranchs and the
fifth branchial arch is without any gill (abranch).
ü Thus, it has nine hemibranchs

24. ü Each gill-pouch has two sets of gill-lamellae, one on its anterior wall and
the other on the posterior. Each set of lamellae is a half gill or hemibranch, so
that gill-pouch has two hemibranches
ü Communicates with the cavity of the pharynx through a large internal branchial
aperture and with the exterior through a narrow external branchial aperture
(commonly called gill- slit)
ü Interbranchial septa is raised into a series of horizontal folds to form
lamelliforms branchial lamellae or gill-filaments
ü Rich blood supply, and they have a very thin covering membrane through
which blood is exposed to sea water for an exchange of gases.

26. b) External Gills
ü External gills are formed as branching outgrowths from the
exposed outer epithelium of gill
ü Arches not from the pharyngeal pouches.
ü They are temporary organs found only in the larval stages
ü They occur in the larva of lampreys, a few bony fishes including
Polypterus, lung fishes (Lepidosiren)

27. 2) Swim bladder/ Air bladder
Origin of lungs in higher vertebrates
ü Most vertebrates develop an out pocketing of pharynx or
oesophagus that becomes one or a pair of sacs (swim bladders or
lungs) filled with gases derived directly or indirectly from the
atmosphere.
ü Similarities between swim bladders & lungs indicate they are the
same organs.
ü Vertebrates without swim bladders or lungs include cyclostomes,
cartilaginous fish, and a few teleosts (e.g., flounders and other bottom-
dwellers).

28. During the ontogenesis of higher vertebrates, the pharyngeal
pouches fail to open to the outside
ü In higher vertebrates, the pharyngeal pouches just remain during the
embryonic period, where they undergo several changes, but very
few or none of their initial characteristics are presented in adults.
ü In amniotes, as in humans, only the first pair of pharyngeal pouches
remains, giving origin bilaterally, the eustachian tube and middle
ear

29. Respiratory system
in Tetrapods

30. ü Most adult amphibians and all amniotes breathe by means of lungs
ü In an embryo a hollow out pushing of single midventral diverticulum (lung
primordial) the ventral wall of the pharynx.
ü It grows backwards and divides into two, right and left lung buds. The
undivided proximal portion develops into trachea and larynx, and opens into
pharynx by glottis.

31. ü In lower forms, the lungs are hollow bags, but in higher forms the ridges
increase in number and unite with one another across the lumen of the
lung to convert it into a solid but spongy structure with innumerable air
spaces
ü In mammals, the internal surface area of lungs may be thirty times that of
the external surface area of the body
Lungs and Duct
Larynx
Trachea
Lungs Proper

32. 1) Larynx
Amphibia
ü Beginnings of larynx are seen in Amphibia
ü Simplest condition (Nectrus), it is supported by a pair of
lateral cartilages, bounding the slit-like glottis
ü In Anura, inner lining of laryngotracheal chamber
forms two muscular bands, or vocal cords, which vibrate to
produce various calls
Birds
ü It is small and rudimentary in birds and
another organ is present , the syrinx
ü Syrinx : located at the lower end of trachea
responsible for sound production.
ü Syrinx tympanum formed of last tracheal cartilage.
Reptiles
ü Larynx is scarcely developed in reptiles

33. Mammals
ü Larynx reaches its greatest point of
evolution in mammals
ü Besides paired arytenoid and single thyroid
cartilage is added on ventral surface of larynx
ü Vocal cords reach maximum
differentiation in mammals
ü A flap of muscular epiglottis is present in
front of glottis and is characteristic of
mammals
ü In singing birds, paired of vibratory membrane called
membrane semilunaris which extend dorsoventrally near the
junction of bronchi and trachea.

34. 2) Trachea
Amphibia
ü Trachea is extremely short or absent in Anura
ü It is merged with the larynx to form laryngotracheal chamber
Reptiles
ü Simple in reptiles as in amphibians or may be long in long-necked
reptiles such as turtles, trachea is long and convoluted
ü Tracheal cartilages are sometimes in the form of complete rings
Birds
ü In birds, the trachea is long. In swans and cranes, trachea is longer
than the neck and tracheal rings are complete and ossified.
Mammals
ü Trachea in mammals is variable and tracheal rings are usually
incomplete on the upper side

35. 3) Lungs
Amphibians
ü In amphibians the lungs are simple, sac-like structures with a
central large cavity.
ü In aquatic amphibians the inner surface of lungs is smooth.
ü In frogs and toads the inner walls contain numerous folds
lined with alveoli so as to increase the respiratory surface.
ü They are richly vascular and lined with mucous epithelium
whose cells are columnar and ciliated.

36. Structure of
respiratory system in
Rana (Frog)

37. Structure of respiratory system in Rana (Frog)

38. Respiratory tract consists of:
ü External nostril
ü Nasal chambers
ü Internal nostrils
ü Bucco-pharyngeal cavity
ü Glottis: On the floor of pharynx, the median slit-like glottis is present Glottis
opens into larynx.
ü Laryngo-tracheal chamber: Larynx or laryngo-tracheal chamber is a thin
walled. Cartilages (2 arytenoid + 1 cricoid) support the walls of larynx
Its internal lining forms a pair of elastic horizontal bands, the vocal cords.
The characteristic croaking is produced because of the vibrations formed when
the air from lungs is forced outside.
Only male frogs have vocal sacs so as to amplify the croaking sound.
ü From larynx, bronchus leads to each lung
ü Two bronchi

41. Lungs in Rana:
ü Lungs are ovoid in structure.
ü They are thin-walled and highly elastic sacs
ü They are suspended freely inside the peritoneal body cavity, one on
either side of the heart
ü Peritoneum covers the lung externally.
ü The inner surface of each lung is divided by septa (a network of folds)
into many small air sacs or alveoli, leaving a clear large central cavity.
ü The alveoli are lined by thin epithelium
ü This epithelium is richly supplied with blood capillaries that contains de-
oxygenated blood for gaseous exchange.
ü O2 in the inhaled air diffused to blood whereas CO2 is released into alveoli.

43. Lungs in Amphibian: Simple, sac-like structure