Gas Exchange O2-CO2

8/14/2019 Gas Exchange O2-CO2

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Gas Exchange

Campbell Chapter 42

Pages 886 - 897


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Gas Exchange in Animals

Gas exchange = taking in

molecular oxygen (O2) from theenvironment and disposing of

carbon dioxide (CO2

) to the

environment.


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Gas Exchange

Cellular respiration is the breakdown oforganic molecules to make ATP. A supply

of oxygen is needed to convert stored

organic energy into energy trapped in ATP. Carbon dioxide is a by-product of these

processes and must be removed from the

cell. There must be an exchange of gases:

carbon dioxide leaving the cell, oxygen

entering.


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Air Supply

The respiratory medium or source of

oxygen is:

1. Terrestrial Animals = air

2. Aquatic Animals = water.

Atmosphere is ~21% oxygen (O2)

Bodies of water variable oxygencontent, but much less than in an equal

amount of air.


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Respiratory Surface

Gases are exchanged with theenvironment at the respiratory surface.

Gas movement is by diffusion.

Respiratory surfaces are usually thin andhave large areas as well as adaptations tofacilitate the exchange.

Gases are dissolved in water, so

respiratory surfaces must be moist.


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Diffusion Rate

The net diffusion rate of a gas across a

fluid membrane is

proportional to the difference in partialpressure,

proportional to the area of the membrane and

inversely proportional to the thickness of the

membrane.


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Ficks Law

The rate at which a substance can diffuse is

given by Fick's law


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Surface to Volume Ratio

Rate of exchange of substances dependson the organism's surface area that is incontact with the surroundings.

The ability to exchange substancesdepends on the surface area : volumeratio.

As organisms get bigger, their volume andsurface area both get bigger, but volumeincreases much more than surface area.


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Unicellular Organisms

Single-celled organisms

exchange gases directlyacross their cellmembrane.

The slow diffusion rate ofoxygen relative to carbondioxide limits the size ofsingle-celled organisms.


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Simple Animals

The cells of sponges, cnidarians, andflatworms are in direct contact withenvironment.

Simple animals that lack specializedexchange surfaces have flattened, tubular,or thin shaped body plans, which are themost efficient for gas exchange. However,these simple animals are rather small insize.


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Simple Animals


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Respiratory Surfaces

Some animals use their outer surfaces

(skin) as gas exchange surfaces.

(earthworms and some annelids) Arthropods, annelids, and fish use gills.

Terrestrial vertebrates utilize internal

lungs.


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Outer Surface (Skin)

Flatworms and annelids use their outer surfaces as gasexchange surfaces. Earthworms have a series ofcapillaries. Gas exchange occurs at capillaries locatedthroughout the body as well as those in the respiratory

surface. Amphibians use their skin as a respiratory surface. Frogs

eliminate carbon dioxide 2.5 times as fast through theirskin as they do through their lungs.

Eels (a fish) obtain 60% of their oxygen through their

skin. Humans exchange only 1% of their carbon dioxide

through their skin.


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Gills

Gills have evolved many times in different

animal groups, and the specific anatomyvaries widely. But as a general rule, gills

consist of fine sheets or filaments of tissue

that extend outward from the body into the

water


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Fish Respiration

Some fish ventilate their gills by swimming with

mouth and gill slits open [e.g. sharks, which die

of asphyxiation if immobilized].

But many fish can respire while stationary, anddo so by swallowing water through their mouths

and forcibly expelling it through the gills.


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Gills

Gills are out-foldings of the body

surface that are suspended in water.

They increase the surface area for gas

exchange. They are organized into a series of

plates and may be internal (as in

crabs and fish) or external to the body

(as in some amphibians).


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Gills


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Who Has Gills?

Gills are found in a variety of animal

groups:

1. arthropods (including some terrestrial

crustaceans)

2. annelids,

3. fish4. amphibians.


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Variety of Gills


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Efficiency of Gills

Gills are very efficient at removing oxygen

from water: there is only about 1/20 the

amount of oxygen present in water as in

the same volume of air.

Water flows over gills in one direction

while blood flows in the opposite direction

through gill capillaries. This countercurrentflow maximizes oxygen transfer.


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How Gills Work

Fish maximize gas exchange in their gills

by a 'design principle' called

countercurrent exchange. Countercurrent exchange requires that two

fluids (in this case, the external water and

the blood in the gills) flow past each otherin opposite directions.


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Counter-Current Exchange

1. When a fish swims, water moves over its gills fromanterior to posterior.

2. Blood flow in the gill capillary bed is oriented fromposterior to anterior. The blood picks up O

2from the

external water (and loses CO2) as it flows through thegill capillaries.

3. This countercurrent arrangement insures that the mostO

2-depleted blood (entering the gill) is confronted with

the most O2 -depleted water (leaving the gill), and thatthe most O2-rich blood (leaving the gill) contacts the

most O2-rich water (entering the gill). This

arrangement maximizes O2absorption.


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Counter-Current Exchange


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Terrestrial Respiratory Systems

Many terrestrial animals have their

respiratory surfaces inside the body and

connected to the outside by a series of

tubes.

Insects, centipedes, and some mites and

spiders have a tracheal respiratory

system.

Vertebrates have lungs.


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Insect Tracheal Systems

All insects are aerobic organisms - they must

obtain oxygen (O2) from their environment in

order to survive. The insect respiratory system is a complex

network of tubes (tracheal system) that delivers

O2-containing air to every cell of the body.

Tracheae are the tubes that carry air directly to

cells for gas exchange.


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Tracheal System

Air enters the insect's body through valve-like

openings (spiracles) in the exoskeleton. These

are located laterally along the thorax and

abdomen of most insects. Air flow is regulated by small muscles that

operate one or two flap-like valves within each

spiracle -- contracting to close the spiracle, or

relaxing to open it.


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After passing through a spiracle, air enters alongitudinal tracheal trunk, eventually diffusingthroughout a complex, branching network of

tracheal tube that subdivides into smaller andsmaller tubes that reach every part of the body.

At the end of each tracheal branch, a special cell(the tracheole) provides a thin, moist interface for

the exchange of gases between atmospheric airand a living cell.

Oxygen in the tracheal tube first dissolves in theliquid of the tracheole and then diffuses into the

cytoplasm of an adjacent cell. At the same time,carbon dioxide, produced as a waste product ofcellular respiration, diffuses out of the cell and,eventually, out of the body through the tracheal

system.


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Insect Tracheal System


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Human Respiratory System


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Human Respiratory System

This system includes the lungs, pathways

connecting them to the outside

environment, and structures in the chest

involved with moving air in and out of thelungs.

The main task of any respiratory system is

to take in oxygen and remove carbondioxide.


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Lungs

Lungs are ingrowths of the body wall andconnect to the outside by as series of

tubes and small openings. Lung breathing probably evolved about

400 million years ago.

Lungs are not entirely the sole property ofvertebrates, some terrestrial snails have agas exchange structures similar to thosein frogs.


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The lungs are large, lobed, paired

organs in the chest (also known as

the thoracic cavity).

Thin sheets of epithelium (pleura)

separate the inside of the chest cavityfrom the outer surface of the lungs.

The bottom of the thoracic cavity is

formed by the diaphragm.


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Pathway of Air

Air enters the body through the nose, is warmed,

filtered, and passed through the nasal cavity.

Air passes the pharynx (which has the epiglottis

that prevents food from entering the trachea). The upper part of the trachea contains the larynx.

The vocal cords are two bands of tissue that

extend across the opening of the larynx.

After passing the larynx, the air moves into the

bronchi that carry air in and out of the lungs.


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Bronchi are reinforced to prevent theircollapse and are lined with ciliated

epithelium and mucus-producing cells. Bronchi branch into smaller and smaller

tubes known as bronchioles.

Bronchioles terminate in grape-like sacclusters known as alveoli.

Alveoli are surrounded by a network ofthin-walled capillaries. Only about 0.2 mseparate the alveoli from the capillariesdue to the extremely thin walls of bothstructures.


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Alveoli

Only in the alveoli does actual gas

exchange takes place.

There are some 300 million alveoli in two

adult lungs.

These provide a surface area of some 160

m2 (almost equal to the singles area of a

tennis court and 80 times the area of our

skin!).


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Alveoli


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Diffusion of O2 and CO2


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Alveoli: Designed for Rapid Gas

Exchange After branching repeatedly the bronchioles enlarge

into millions of alveolar sacs This arrangement produces an enormous surface

are for gas exchange

Each alveolus is surrounded by a net of capillaries The diffusion distance from gas in the alveoli to

blood cells in the capillaries is very short Blood takes about 1 second to pass through the

lung capillaries In this time the blood becomes nearly 100%saturated with oxygen and loses its excess CO2


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Surfactants Prevent the Alveoli

From Collapsing

At air/water interfaces there is a high surfacetension

The high surface tension would cause the alveoli to

collapse, but this is prevented by surfactants

Surfactants are detergent-like phospholipids whichaccumulate at the air/water interface and lower thesurface tension

Reduced surfactant causes respiratory distresssyndrome (seen in premature infants and someolder persons)


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Pigments Respiratory pigments increase the oxygen-

carrying capacity of the blood. Humans have thered-colored pigment hemoglobin as theirrespiratory pigment.

Hemoglobin increases the oxygen-carrying

capacity of the blood between 65 and 70 times. Each red blood cell has about 250 millionhemoglobin molecules, and each milliliter ofblood contains 1.25 X 1015 hemoglobinmolecules.

Oxygen concentration in cells is low (whenleaving the lungs blood is 97% saturated withoxygen), so oxygen diffuses from the blood tothe cells when it reaches the capillaries.


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Animation

http://www.mdhs.unimelb.edu.au/bmu/exampl

http://science.nhmccd.edu/biol/respiratory/alv

http://www.smm.org/heart/lungs/breathing.ht

http://

sprojects.mmi.mcgill.ca/resp/anatomy.swf
http://www.mdhs.unimelb.edu.au/bmu/examples/gasxlung/http://science.nhmccd.edu/biol/respiratory/alveoli.htmhttp://www.smm.org/heart/lungs/breathing.htmhttp://sprojects.mmi.mcgill.ca/resp/anatomy.swfhttp://sprojects.mmi.mcgill.ca/resp/anatomy.swfhttp://sprojects.mmi.mcgill.ca/resp/anatomy.swfhttp://sprojects.mmi.mcgill.ca/resp/anatomy.swfhttp://www.smm.org/heart/lungs/breathing.htmhttp://science.nhmccd.edu/biol/respiratory/alveoli.htmhttp://www.mdhs.unimelb.edu.au/bmu/examples/gasxlung/


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Ventilation

Ventilation is the mechanics of breathingin and out.

When you inhale, muscles in the chest

wall contract, lifting the ribs and pullingthem, outward. The diaphragm at this timemoves downward enlarging the chestcavity. Reduced air pressure in the lungscauses air to enter the lungs.

Exhaling reverses theses steps.


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Diaphragm Action


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Negative Pressure Animation


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Lung Volume

Tidal volume is the amount of air that is

inhaled and exhaled in a normal breath.

Vital capacity is the maximum amount of

air that can be inhaled and exhaled in a

single breath.

Since the lungs hold more air than the vital

capacity, the air that remains in the lungsis the residual volume.


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Dead Space

Only the air in the alveoli can exchange O2 andCO2 with the blood

When you breath in the first 150 mL fills tubeswhich are outside of the alveoli (trachea, bronchi,

bronchioles, etc.) This part of the tidal volume is called the

anatomical dead space- it does not participate ingas exchange

There is also a functional dead space- not all ofthe alveoli are perfused with blood; air in thesealveoli doesn't exchange with the blood and ispart of the dead space


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Avian Respiration

The avian respiratory system delivers

oxygen from the air to the tissues and also

removes carbon dioxide.

In addition, the respiratory system plays

an important role in thermoregulation

(maintaining normal body temperature).


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The avian respiratory system is different

from that of other vertebrates, with birds

having relatively small lungs plus nine airsacs that play an important role in

respiration (but are not directly involved in

the exchange of gases).

Th i it idi ti l fl f


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The air sacs permit a unidirectional flow ofair through the lungs.

Unidirectional flow means that air movingthrough bird lungs is largely 'fresh' air &has a higher oxygen content.

In contrast, air flow is 'bidirectional' in

mammals, moving back & forth into & outof the lungs. As a result, air coming into amammal's lungs is mixed with 'old' air (air

that has been in the lungs for a while) &this 'mixed air' has less oxygen. So, in birdlungs, more oxygen is available to diffuseinto the blood


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Respiration

http://www.wisc-online.com/objects/framz.asp
http://www.wisc-online.com/objects/framz.asp?objID=AP2404http://www.wisc-online.com/objects/framz.asp?objID=AP2404


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Credits

All material for this PPT was found on

various websites or is from Campbell

Biology 6e.

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Gas Exchange O2-CO2

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