Respiratory System

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Outline

• Respiratory structures– Gills– Air-Breathing Animals– Amphibians and Reptiles– Mammals

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– Mammals– Birds

• Structures and Mechanisms of Breathing

Fig. 44.19(TE Art)Copyright © The McGraw-Hill Companies, Inc. Permiss ion required for reproduction or display.

O2CO2 O2CO2

Epidermis

Blood vessel

O2

CO2

Epidermis

Pap-ula

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Blood vessel

Spiracle

Alveoli

O2

O2

CO2

O2

O2

CO2

CO2

CO2

Trachea

Gases

• Air is – 21% oxygen– 78% nitrogen– Less than 1% carbon dioxide and other

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gases• Nitrogen gas usually ignored because it is

not part of the respiratory process

The Gill as a Respiratory Structure

• External gills provide a greatly increased surface area for gas exchange.

– disadvantages are that they must be moved constantly and are easily damaged

Gills of bony fish

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• Gills of bony fish– located between buccal cavity and

opercular cavity

Bony Fish Respiration

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The Gill as a Respiratory Structure

• Buccal cavity can be opened and closed by opening and closing the mouth.

• Opercular cavity can be opened and closed by movements of the operculum.

– ram ventilation

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– ram ventilation� blood flows in an opposite direction to

the flow of water, thus maximizing oxygenation of blood

�gill arches� countercurrent flow

Structure of a Fish Gill

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Respiration in Air-Breathing Animals

• Gills replaced in terrestrial animals because:– air is less buoyant than water– water vapor diffuses into the air through

evaporation• Two main terrestrial respiratory organs:

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• Two main terrestrial respiratory organs:– tracheae– lung

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

Respiration in Amphibians and Reptiles

• 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

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� 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.

Amphibian Lungs

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Respiration in Mammals

• Lungs 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.

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through glottis into the trachea.�Bifurcates into right and left bronchi

which enter each lung and further subdivide into bronchioles that deliver air into alveoli.

Human Respiratory System

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Mammalian respiratory systems

• Nose and mouth – air is warmed and humidified

• Mucus in the nose cleans the air of dust• Pharynx• Larynx – vocal cords

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• Larynx – vocal cords• Trachea – glottis (opening to trachea)

protected by epiglottis, rings of cartilage, cilia and mucus trap particles

• Lungs

• Trachea branches into 2 bronchi• Bronchioles – surrounded by circular muscle

to dilate or constrict passage• Alveoli – site of gas exchange

– One cell thick

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– One cell thick– Coated with extracellular fluid for gases to

dissolve– Surfactant prevents alveoli from collapsing

Respiration in Birds

• Bird lung channels air through tiny air vessels called parabronchi, where gas exchange occurs.

– unidirectional flowWhen air sacs are expanded during

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• 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.

Respiration in Birds

• Avian 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

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extract more oxygen from the air than a mammalian lung.

How A Bird Breathes

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Structures and Mechanisms of Breathing

• The outside of each lung is covered by a visceral pleural membrane.

– Second parietal pleural membrane lines inner wall of thoracic cavity.

pleural cavity between the two

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� pleural cavity between the two membranes

Fig. 44.28(TE Art)Copyright © The McGraw-Hill Companies, Inc. Permiss ion required for reproduction or display.

Abdominal

ExpirationInspiration

Sternocleido-mastoidmuscles contract(for forced inspiration)

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Abdominal musclescontract (for forcedexpiration)

Musclescontract

Musclesrelax

Diaphragmcontracts

Diaphragmrelaxes

Hemoglobin and Oxygen Transport

• Hemoglobin 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

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• Hemoglobin loads up with oxygen in the lungs, forming oxyhemoglobin.

– As blood passes through the capillaries, some of the oxyhemoglobin releases oxygen and become deoxyhemoglobin.

Carbon Dioxide Transport by the Blood

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