External pore or common duct (not a slit)

Fifteen to five pouches and associated pores

Gill septa and gill slits arranged parallel

Gill septa longer than gill filaments

First gill slit reduced to spiracle

Larger openings into pharynx than in

Four holobranchs plus one demibranch

Gill septa reduced and shorter than gill

filaments

Bony operculum present-protects filaments

Operculum contributes to ventilation of gills

Holobranchs reduced to three or less

Ventilation of Internal Gills

Pouched Gills-Tidal respiration

Water actively expelled from pouches by muscular contraction. Visceral skeleton allows cartilage to rebound and create suction-allowing water to re-enter the pouches.

Septal Gills-

Suction Phase

Pharynx contracts and expels water out of gill slits and mouth

Recoil from contractions creates buccal cavity suction. Water rushes in

branchial muscles enlarge creates suction. Water rushes in

1. Mouth and operculum are closed and compressed
2. Buccal cavity expands, opercular cavity expands
3. Mouth opens-water rushes into buccal cavity then opercular cavity.

Force Phase

4. Mouth closes, operculum opens
5. Buccal cavity compresses and operculum remains open
6. Buccal cavity compresses and opercular cavity compresses

Ram ventilation-moving through the water with an open gape to ventilate the lungs. Only works while moving forward.

Evolution of lungs

More than 20 genera of fishes are habitual air-breathers. There are some species of fish that will drown if they are prevented from gulping air periodically.

In drought situations, gills are detrimental because they dry out easily. Oxygen intake, not carbon dioxide expulsion is a limiting factor. In other words, gills can continue to rid the body of CO2 even if they are not useful in taking up oxygen.

Lungs are any paired or unpaired structures that are derived from the gut tube and are filled with air and function primarily in respiration.

Internal organs filled with gas but are not respiratory structures are called gas bladders.

Gas bladders only occur in bony fishes

The respiratory system of amniotes develops from a single ventral evagination of the gut tube right behind the pharynx.

The early evagination quickly buds off into two

Two types of gas bladders/lungs

Physostomous (bladder mouth)-have a pneumatic duct attached near the pharynx

Physoclistous (bladder closed)-a gas bladder lacking a pneumatic duct-more specialized fish

Gas bladders make up between 4 and 11% of the body mass of fish.

Long, short, curved, straight, simple, or partitioned into two or three distinct parts

Usually lies above the center of gravity-allows the fish to maintain a vertical position without expending muscular energy.

Other fish have to use their fins to prevent rolling if the gas bladder is underneath the center of gravity (or swim upside down).

Gas is usually secreted into the gas bladder in Physoclistous bladders by GAS GLANDS

Underneath each gas gland is a rete mirabile (marvelous net) of capillaries all oriented in the same direction. Efferent and Afferent capillaries exchange gas at a maximum gradient (through countercurrents) to maintain maximum gas pressure.

But the oxygen content may reach 1000 times that of the surrounding water and the partial pressure of oxygen may be 200 atm.

Some deep sea fishes have no gas bladder, others do.

Fish that tend to remain at a constant level or inhabit shallow streams often lack a gas bladder or have one reduced in size.

Flounders and Halibut have no gas bladder.

How do gas bladders differ from lungs?

Gas bladders are usually stiuated dorsal to the digestive tract whereas lungs are ventral

Gas bladders are single, whereas lungs are usually paired.

For gas bladders used as lungs, how are they ventilated?

Gas bladder breathing is usually done using tidal ventilation or pulse ventilation.

In this case, for exhalation, the sphincter muscle surrounding the glottis relaxes and brings swallowed air into the buccal cavity where it is expelled or vented through the operculum.

Inhalation-takes in air into mouth.

Closes mouth and compresses air to force it into gas bladder/lung

Movement of the air may be helped by compression of the outside water environment.

A few fish use unidirectional breathing when they use a vascularized stomach for respiration. In this case, the fish passes the air all the way through the digestive tract.

Amphibians use the same mechanism to get air into the lungs, but the buccal cavity muscles are stronger.

1) Dual Pump-unidirectional

Suction phase

Force phase

2) Ram Ventilation-unidirectional

1) Pulse pump-bidirectional (tidal)

Exhalation-sphincter relaxation, expel air

2) Stomach ventilation-unidirectional

Exhalation-pass gas through rectum

(birds, reptiles, mammals)

Diaphragm drops-creates suction

Exhalation-intercostals contract rib cage

Diaphragm is raised-pushes air out.

Gas Bladder Function

Change buoyancy in water

Respiration

Sound production

Sound or pressure reception

Terrestrial Lung structure

Elastic bag

Surfactants coating the passages

Change buoyancy in water

Physostomous (bladder mouth)-

lacking a pneumatic duct

Lined with blood vessels

resonating chamber-teeth grinding

Belching, drumming

Used to moderate food and air transport

Bronchioles (secondary, tertiary etc)

Alveoli and Faveoli

Elastic air bags with surfactants

Breathing Mechanisms within select Vertebrates

Amphibians

1. Closes mouth and nares, elevate bottom of mouth
2. Air is forced into lungs
3. Mouth and nares open, thorax compressed-air is forced out of lungs

Reptiles

Posterior portion of snake lungs may serve the same function as a diaphragm-bellows

Crocodilians use a diaphragm from the abdomen and pull the diaphragm back…piston-like. Connective tissue attaches the liver to the diaphragm

Mammals

Diaphragm acts directly. Forms a tight seal between abdominal and thoracic cavitities-only the vena cava, aorta, and esophagous pass through it.

Locomotion may cause breathing to cycle with strides.

Abdominal viscera may be used as part of the pump.

External intercostals-inhalation

Internal intercostals-exhalation-or through gravity

10 times the respiratory surfaces of amphibians-higher metabolic rate

Trachea

Parabronchi

One way branches

Air capillaries

Nine air sacs are connected to lungs

Interclavicular

2 cervicals

2 anterior thoracic

2 posterior thoracic

2 abdominal

Air is drawn into Parabronchi and posterior air sacs

Two cycles of ventilation to remove air in respiratory system.

Trachea branches into posterior thoracic and abdominal air sacs first