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Respiration - process of obtaining oxygenfrom the external environment & eliminatingCO2.
Two Types of Respiration
1. External respiration - oxygen andcarbon dioxide exchanged between theexternal environment & the body cells.
- takes place in fetal membranes, at
the surface of the skin, in gills and in lungs.2. Internal Respiration essential gases
are then exchanged with the tissues in therespective capillary beds.
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Efficiency of external respiration is increased
by providing a large surface of contact
between the water or air and the blood, andby maintaining the contact of each blood cell
with the medium for an adequate time.
Ventilation pumping of water in gills and of
air in lungs.Common Respiratory Organs
1. Gills
2. Cutaneous Respiration
3. Larval Gills
4. Swim Bladder and Lungs
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Basic structure of internal gills is similar for all
fishes:
Each gill bar consists of a part of a visceral skeleton,
blood vessels derived from the corresponding aortic
arch, cranial or cervical nerves intrinsic branchialmuscles and the related epithilium
Bars may or may not be extended by gill septa
Most bars carry one or more rows of gill rakers
Each gill bar bears two rows of gill filaments calledprimary filaments that is strengthen by fine skeletal
gill rays
a bar with filaments forms a partition between
adjacent gill chambers
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Exchange of oxygen and carbon dioxide between blood and
water.
Excretion and osmoregulation (Bony Fishes)
Gills of freshwater bony fishes admit water and absorb
salts while gills of marine bony fishes pass water and
excrete salts.
Types of Internal Gills
Pouched gills (Agnathans)
- gill filaments are arranged over the surface of discrete,
pouch like gill chambers
Septal gills (Elasmobranchs)
- Gill chambers tend to be longer to communicate more
widely with the pharynx internally and externally
through the vertical gill slits instead of pores.
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Opercular gills (Osteichthyes)
- septa are usually shorter that their
filaments or even absent so that the gill barsremain to anchor the gill filaments.
- gills of teleost are the most efficientrespiratory organ.
Types of Gill Bars Holobranch if it bears anterior and
posterior rows of filaments
Hemibranch if it bears on the surface only
Pseudobranch - if the filaments on theposterior surface of the mandibular arch aremodified to serve a non respiratoryfunction.
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Present in protochordates , important in food
getting, connection with a ciliated groove, the
endostyle.
Serve as respiration and in food getting
(amphioxus).Number of gills slits is greater in lower forms and
lesser in higher forms:
- Amphioxus (140+) - Modern fishes (5)
- Hagfishes (7 to 14 pairs) - Teleosts (4)
- Lampreys ( 6 pairs) - Amphibians (3)
- Sharks ( 5 slits)
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Development of internal gills is related to the
pharynx.Pharynx portion of the foregut that lies between
the developing oral cavity and the esophagus lined byendoderm.
In agnatha, the first pharyngeal pouch becomes a
typical gill chamber. In other fishes, the first pharyngeal pouch is lost or
is reduced in size and in function.
In Tetrapods, the first pouch becomes the cavity ofthe middle ear, most posterior pouches form gill
chambers.
Some larval amphibians lose their pouch- likecharacter after contributing glandular andlymphatic tissues from their epithelial linings.
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Ostracoderms took water into the pharynxthrough the mouth, passed it through the gillpouches and expelled it from the headthrough the branchial pores.
Cyclostomes also expel water through
branchial pores but water enters and leavesthe gill pouches from the external branchialpores
Elasmobranchs draw water into the pharynx
through the mouth and spiracles. Some active teleosts swim continuously and
water constantly enters through the gills bythe swimming process.
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Internal organs that are filled with air andfunction primarily in respiration.
Gas Bladders Internal organs that are filledwith gas but are not respiratory in function.
more than 20 genera of Bony fishes are habitual
air breathers In anurans and caecilians, the lungs develop
from the paired lateral evaginations of the guttube.
The lungs of amniotes develop from a single,ventral evaginations of paired areas of endodermlocated posterior to the pharyngeal pouches.
Lungs evolved during the Devonian period
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Anura have large but short lungs, the wallshave several partitions to provide a totalrespiratory surface of 1cm/g body weight butvarying inversely with the effectiveness of
cutaneous respiration Apoda usually retain only the right lung,
labyrinthodonts had the most advanced lungsof the class resembling those of reptiles
Urodela have simpe, long and slender sacswith smooth walls; most species have losttheir lungs entirely, skin or gills servingrespiratory function instead.
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Lungs of Reptiles
- Partitions can be sparse or dense, shallow or deep,
evenly or unevenly distributed.
- trachea and bronchi are larger and supported bycartilaginous rings
- each bronchus enters the lungs near the middle or
anterior end but not at the apex
- larynx is consists of cricoid and arytenoids cartilages that
are joined by the hyoid apparatus. Lungs of Mammals (More efficient)
- lobes may be absent but usually there are at least two
lobes on the left and three lobes on the right.
-smooth muscles and mucous glands are present in the
walls
- the trachea divides into right and left primary bronchi
that divides into smaller bronchi which further divide into
numerous membranous bronchioles.
- these nonciliated brochioles open into alveolar ductsystem which are clusters of 10 to 30 alveoli, where actual
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May be located high in the body cavity to
enable the fish to remain upright withoutexpending muscular effort.
Gas bladders may be long or short, straightor curved, simple or partitioned into two or
three lobes. Physostomous If the gas bladder functions
as a lung. Joined by the pneumatic duct.
Physoclistous if the gas bladder is not
respiratory in function. No pneumatic duct physoclist bladder => hydrostasis
=> sound production
=> pressure reception
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Air breathing Actinopterygian fishes uses two
cycle sequence;
- the pharynx expands drawing expired gas
from the lungs into the buccal cavity- pharynx contracts forcing this gas to exit
through the open mouth of gill chambers
- fresh air enters the buccal cavity through
the mouth- with mouth closed, the pharyx force the
air into the lungs.
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Anurans are pulse pump breathers
Ventilation by aspiration is more efficient
- inspiration is by negative pressure created inthe thoracic or abdominal cavities.
- expiration is either passive or results from
constriction of these cavities.
- one cycle system with simpler but efficient
Labyrinthodonths => first aspiration breathers
- breathing was interrupted by locomotion just
like in lizards.Crocodilians have diaphragmatic muscle which
pulls the liver toward the pelvis sucking the
lungs that causes inhalation.
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Turtles inhale when muscles crossing the limb
apertures of the shell enlarge the internal
cavity.
Inhalation and exhalation of snakes is forced
by the action of muscles inserted on the ribs
and ventral skin.
Respiration of Birds involves differentmuscles;
- sternum is actively rocked downward and
forward for inspiration and is raised for
expiration. Lungs of mammals are inflated by the
negative pressure resulting from the
contraction of the dome shaped diaphragm
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