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Respiration

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Outline

• How Animals Maximize Rate of Diffusion– Gills– Air-Breathing Animals– Amphibians and Reptiles– Mammals– Birds

• Structures and Mechanisms of Breathing

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Principle of Gas Exchange in Animals

• Rate of diffusion between two regions is governed by Fick’s Law of Diffusion.

R = D x A ( p/d)– R = rate of diffusion– D = diffusion constant– A = area over which diffusion takes place p = differences in concentrations– d = distance across which diffusion takes

place

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How Animals Maximize the Rate of Diffusion

• beating cilia producing water current• respiratory organs that increase surface

area available for diffusion– bring external environment close to

internal fluid• atmospheric pressure and partial pressures

– one atmosphere is 760 mm Hg– partial pressure is fraction contributed by a

gas

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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– located between buccal cavity and

opercular cavity

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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 blood flows in an opposite direction to

the flow of water, thus maximizing oxygenation of blood

gill arches countercurrent flow

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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:

– tracheae– lung

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

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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 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.

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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.Bifurcates into right and left bronchi

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

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Human Respiratory System

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Respiration in Birds

• Bird 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 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 mammalian lung.

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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 membranes

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Structures and Mechanisms of Breathing

• Mechanics 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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Gas Exchange

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Structures and Mechanisms of Breathing

• Breathing 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 Breathing

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

(a) (b)

Abdominal musclescontract (for forcedexpiration)

ExpirationInspiration

Musclescontract

Musclesrelax

Sternocleido-mastoidmuscles contract(for forced inspiration)

Diaphragmcontracts

Diaphragmrelaxes

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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 group• 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.

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Hemoglobin and Oxygen Transport

• Oxygen transport– Oxygen transport in the blood is affected

by many conditions. pH - Bohr effect

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Carbon Dioxide and Nitric Oxide Transport

• About 8% of CO2 in blood is dissolved in plasma and another 20% is bound to hemoglobin.

– Remaining 72% of CO2 diffuses into red blood cells where carbonic anhydrase catalyzes the combination of CO2 with water to form carbonic acid.

• Blood flow and blood pressure are also regulated by the amount of NO released into the bloodstream.

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Carbon Dioxide Transport by the Blood