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Gas Exchange: Respiration

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Gas exchange occurs across specialized respiratory surfaces

• Gas exchange

– Supplies oxygen for cellular respiration and disposes of carbon dioxide

Figure 42.19

Organismal level

Cellular level

Circulatory system

Cellular respiration ATPEnergy-richmoleculesfrom food

Respiratorysurface

Respiratorymedium(air of water)

O2 CO2

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• Animals require large, moist respiratory surfaces for the adequate diffusion of respiratory gases

– Between their cells and the respiratory medium, either air or water

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• In mammals, air inhaled through the nostrils

– Passes through the pharynx into the trachea, bronchi, bronchioles, and dead-end alveoli, where gas exchange occurs

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Gas exchange: occurs in alveoli of lungs, diffusion of oxygen and carbon dioxide through capillaries

• Ventilation: bringing in fresh air into the alveoli (breathing)

• Cellular respiration: produces ATP for the cell, uses oxygen and produces carbon dioxide.

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Mammalian Respiratory Systems: A Closer Look

• A system of branching ducts

– Conveys air to the lungsBranch from the pulmonary vein (oxygen-rich blood) Terminal bronchiole

Branch from thepulmonaryartery(oxygen-poor blood)

Alveoli

Colorized SEMSEM

50 µ

m

50 µ

m

Heart

Left lung

Nasalcavity

Pharynx

Larynx

Diaphragm

Bronchiole

Bronchus

Right lung

TracheaEsophagus

Figure 42.23

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Alveoli

• Very small but huge in numbers (large surface area for gas exchange)

• Made up of a single layer of thin cells

• Covered by a dense network of blood capillaries

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How a Mammal Breathes

• Mammals ventilate their lungs by breathing

– By negative pressure breathing, which pulls air into the lungs

Air inhaled Air exhaled

INHALATIONDiaphragm contracts

(moves down)

EXHALATIONDiaphragm relaxes

(moves up)

Diaphragm

Lung

Rib cage expands asrib muscles contract

Rib cage gets smaller asrib muscles relax

Figure 42.24

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Inhalation:

• External intercostal muscles contract (moves rib cage up and out)

• Diaphragm contracts

• Increase in volume, drop in pressure (below atmospheric pressure)

• Air flows into lungs until pressure inside lungs rises to atmospheric pressure.

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Exhalation

• Internal intercostal muscles contract (moves rib cage down and in)

• Abdominal muscles contract, pushing up diaphragm

• Decrease in volume, pressure rises above atmospheric pressure

• Air flows out of lungs until the pressure in lungs falls back to atmospheric pressure.

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Why do we need a ventilation system???• Maintain the concentration gradients of gases

(oxygen/carbon dioxide) in the alveoli.

– Carbon dioxide needs to be low in alveoli so it moves into the alveoli from capillaries.

– Oxygen needs to be high in alveoli so it can move into capillaries.

– Ventilation makes this possible by getting rid of carbon dioxide and bringing in oxygen

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The Role of Partial Pressure Gradients

• Gases diffuse down pressure gradients

– In the lungs and other organs

• Diffusion of a gas

– Depends on differences in a quantity called partial pressure

• A gas always diffuses from a region of higher partial pressure

– To a region of lower partial pressure

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• In the lungs and in the tissues

– O2 and CO2 diffuse from where their partial pressures are higher to where they are lower

– RESPIRATION

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Inhaled air Exhaled air

160 0.2O2 CO2

O2 CO2

O2 CO2

O2 CO2 O2 CO2

O2 CO2 O2 CO2

O2 CO2

40 45

40 45

100 40

104 40

104 40

120 27

CO2O2

Alveolarepithelialcells

Pulmonaryarteries

Blood enteringalveolar

capillaries

Blood leavingtissue

capillaries

Blood enteringtissue

capillaries

Blood leaving

alveolar capillaries

CO2O2

Tissue capillaries

Heart

Alveolar capillaries

of lung

<40 >45

Tissue cells

Pulmonaryveins

Systemic arteriesSystemic

veinsO2CO2

O2

CO2

Alveolar spaces

12

43

Figure 42.27

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Respiratory Pigments

• Respiratory pigments

– Are proteins that transport oxygen

• Greatly increase the amount of oxygen that blood can carry

• The respiratory pigment of almost all vertebrates

– Is the protein hemoglobin, contained in the erythrocytes

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• Like all respiratory pigments

– Hemoglobin must reversibly bind O2, loading O2 in the lungs and unloading it in other parts of the body

Heme group Iron atom

O2 loadedin lungs

O2 unloadedIn tissues

Polypeptide chain

O2

O2

Figure 42.28