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Respiratory SystemsChapter 48

Primary functionGas Exchange

◦ Moves oxygen between the air and blood and between blood and cells

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Composition of Air21% oxygen78% nitrogenLess than 1%

carbon dioxide and other gases

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Atmospheric Pressurepressure exerted by

the atmosphere on the body surfaces of animals◦ Decreases with

altitudeProvides the driving

force for diffusion of oxygen in air or water

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Diffusion of GasesReadily dissolve in

solution◦ Fresh water◦ Sea water◦ Body fluids

Water is a poor solvent for gases◦ Influenced by:

Atmospheric pressure Temperature Presence of other

solutes

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Adaptations for Gas Exchange

Single cellCutaneusPapulaTracheal systemGillsLungs

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Adaptations for Gas ExchangeArose as demands for cellular

respiration increased◦ Linked to increase in size of organisms

Efficiency dependent on:◦ Surface area over which diffusion takes

place◦ The distance over which diffusion takes

place◦ The concentration gradient

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Features of Respiratory OrgansMoist surfaces in which gases

dissolve and diffuseIncreased surface area for gas

exchangeExtensive blood flowThin, delicate structure

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Body Surfaces for gas exchangeInvertebrates with one or a few

cell layers can use diffusion for gas exchange

Some do not even need specialized transport mechanisms

Some large, complex animal body surfaces may be permeable to gases◦Amphibians are the only vertebrates

to rely on their skin for gas exchange under water

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Percentage of gas exchange through the skin0 10 20 30 40 50 60 70 80 90 100

Lungless salamander

Lungless salamander(Ensatina eschscholtzii)

Bullfrog(Rana catesbeiana)

Mudpuppy(Necturus maculosus)

Southern musk turtle(Sternotherus minor)

European eel(Anguilla anguilla)

Boa constrictor(Constrictor constrictor)

Green lizard(Lacerta viridis)

Big brown bat(Eptesicus fuscus)

Brown trout(Salmo trutta)

Human(Homo sapiens)

O2

CO2

a: © Ken Lucas/Visuals Unlimited

The Gill as a Respiratory StructureExternal gills provide a greatly

increased surface area for gas exchange.◦disadvantages are that they must be

moved constantly and are easily damaged

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The Gill as a Respiratory StructureInternal Gills of bony fish

◦located between buccal cavity and opercular cavity

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Structure of a Fish Gill

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A Closer Look

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Gill arch

Lamella

Gill filament

Gill arch

Gill filaments

Lamellae

Lamella

Direction of H2O flow

Afferentfilamentblood vessel

Direction ofblood flow

Efferentfilamentbloodvessel

Direction ofwater flow

Waterflow

Afferentfilamentblood vessel

Efferentfilamentblood vessel

O2 content

Bloodflow

Direction ofO2 movement

100%

70%

40% 15%

90%

60%

30% 5%

Ventilation of GillsBuccal pumping

◦ hydrostatic pressure gradient created by lowering jaw to suck water in and opening operculum to draw water through

Ram ventilation◦ swimming with

mouth open15

Respiration in Air-Breathing AnimalsGills replaced in terrestrial

animals Two main terrestrial respiratory

organs:◦tracheae◦lung

Lungs use a uniform pool of air in constant contact with gas exchange surface.

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Tracheae of InsectsSpiracles on the body surface lead to

tracheae that branch into tracheoles terminating near every body cell

Small amount of fluid for gas to diffuse intoMuscular movements of body draw air into

and out of tracheaeOpen circulatory system of insect not used in

gas exchangeOxygen diffuses directly from air to tracheae

to tracheoles to body cellsVery efficient – supports insect flight muscles

with highest metabolic rate known

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Spiracle

Trachea

Muscle

Tracheoles 0.4 mm

Tracheole

Bodysurface

(inset): © Ed Reschke/Peter Arnold

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Respiration in Amphibians and Reptiles

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Lungs of amphibians are formed as saclike outpouching of the gut.◦Amphibians force air into their lungs

creating positive pressure. fill buccal cavity with air, and then close

mouth and nostrils and elevate floor of oral cavity

◦Reptiles expand their rib cages by muscular contraction and take air into lungs via negative pressure breathing.

Positive Pressure in Amphibians

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Respiration in MammalsLungs of

mammals packed with alveoli.◦ Air brought to

alveoli through system of air passages. Inhaled air taken to

the larynx, passes through glottis into the trachea. right and left

bronchi bronchioles alveoli.

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Inspiration

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Respiration in BirdsBird lung channels air through tiny air

vessels called parabronchi, where gas exchange occurs.◦ unidirectional flow

When air sacs are expanded during inspiration, they take in air.

When they are compressed during expiration, they push air into and through the lungs.

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Respiration in BirdsAvian respiration

occurs in two cycles.◦Each cycle has

an inspiration and an expiration phase. Cross-current flow

has the capacity to extract more oxygen from the air than a mammalian lung. 24

ANIMATION

Mammalian Respiratory SystemsNose and mouth

◦ Air is warmed and humidified

◦ Mucus and hairs in the nose cleans the air of dust

PharynxLarynx

◦ Vocal cordsTrachea

◦ Glottis (opening to trachea) protected by epiglottis, rings of cartilage, cilia and mucus trap particles

Mammalian Respiratory SystemsTrachea

◦ branches into 2 bronchi

Bronchioles◦ surrounded by

circular muscle to dilate or constrict passage

Alveoli◦ site of gas

exchange One cell thick

Type I cells – gases diffuse across

Type II cells – secretory cells

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Structures and Mechanisms of BreathingPleural sac

encases each lung◦ Double layer of

thin, moist tissue◦ Fluid between

layers acts as lubricant and makes layers adhere to each other

◦ Movements of chest wall will result in lung also moving

◦ Lungs will be inflated by expansion of the chest wall

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Structures and Mechanisms of BreathingMechanics of breathing

◦Boyle’s Law - when the volume of a given quantity of gas increases, its pressure decreases When the pressure within the lungs is

lower than the atmospheric pressure, air enters the lungs.

◦Thoracic volume increased by contraction of external intercostals and the diaphragm.

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Tidal VentilationInhalation

◦ intercostals contract to move chest wall up and out, diaphragm contracts and drops down – thoracic cavity enlarges, pressure drops, air sucked in

Exhalation◦ intercostals and diaphragm relax –

thoracic cavity compressed, pressure increases, air pushed out

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After exhaling

Structures and Mechanisms of BreathingBreathing measurements

◦tidal volume - volume of air moving into and out of the lungs

◦vital capacity - maximum amount of air that can be expired after a forceful inspiration

◦hypoventilating - slow breathing - too much carbon dioxide

◦hyperventilating - rapid breathing - not enough carbon dioxide

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Mechanisms That Regulate BreathingRise in carbon dioxide causes

blood pH to lower, stimulating neurons in the aortic and carotid bodies to send impulses to the control center in the medulla oblongata.◦Sends impulses to diaphragm and

external intercostal muscles, stimulating them to contract, expanding chest cavity.

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Hemoglobin and Oxygen TransportHemoglobin is a protein

composed of four polypeptide chains and four organic heme groups.◦iron atom at center of each heme

groupHemoglobin loads up with oxygen

in the lungs, forming oxyhemoglobin.◦As blood passes through the

capillaries, some of the oxyhemoglobin releases oxygen and become deoxyhemoglobin.

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