the respiratory system and gas exchange.doc

8/10/2019 The Respiratory System and Gas Exchange.doc

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The Respiratory System and Gas Exchange| Back to Top

Cellular respirationinvolves the breakdown of organic molecules to produce

ATP. A sufficient supply of oxygen is required for the aerobic respiratory

machinery of Krebs Cycle and the !lectron Transport "ystem to efficientlyconvert stored organic energy into energy trapped in ATP. Carbon dioxide is

also generated by cellular metabolismand must be removed from the cell.

There must be an exchange of gases# carbon dioxide leaving the cell$ oxygen

entering. Animals have organ systems involved in facilitating this exchange as

well as the transport of gases to and from exchange areas.

Bodies and Respiration| Back to Top

"ingle%celled organisms exchange gases directly across their cell membrane.

&owever$ the slow diffusionrate of oxygen relative to carbon dioxide limits thesi'e of single%celled organisms. "imple animals that lack speciali'ed exchange

surfaces have flattened$ tubular$ or thin shaped body plans$ which are the most

efficient for gas exchange. &owever$ these simple animals are rather small in

si'e.

Respiratory Surfaces| Back to Top

(arge animals cannot maintain gas exchange by diffusion across their outer

surface. They developed a variety of respiratory surfacesthat all increase the

surface area for exchange$ thus allowing for larger bodies. A respiratory surfaceis covered with thin$ moist epithelial cellsthat allow oxygen and carbon

dioxide to exchange. Those gases can only cross cell membranes when they are

dissolved in water or an aqueous solution$ thus respiratory surfaces must be

moist.

Methods of Respiration| Back to Top

"ponges and )ellyfish lack speciali'ed organs for gas exchange and take in

gases directly from the surrounding water. *latworms and annelids use their

outer surfaces as gas exchange surfaces. Arthropods$ annelids$ and fish use

gills+ terrestrial vertebrates utili'e internal lungs.
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,as exchange systems in several animals.-mages from Purves et al.$ (ife# The"cience of iology$ /th !dition$ by "inauer Associates 0www.sinauer.com1 and 2&

*reeman 0www.whfreeman.com1$ used with permission.
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The Body Surface

*latworms and annelids use their outer surfaces as gas exchange surfaces.

!arthworms have a series of thin%walled blood vessels known as capillaries.

,as exchange occurs at capillaries located throughout the body as well as those

in the respiratory surface.

Amphibians use their skin as a respiratory surface. *rogs eliminate carbon

dioxide 3.4 times as fast through their skin as they do through their lungs. !els

0a fish1 obtain 567 of their oxygen through their skin. &umans exchange only

87 of their carbon dioxide through their skin. Constraints of water loss dictate

that terrestrial animals must develop more efficient lungs.

Gills

,ills greatly increase the surface area for gas exchange. They occur in a varietyof animal groups including arthropods 0including some terrestrial crustaceans1$

annelids$ fish$ and amphibians. ,ills typically are convoluted outgrowths

containing blood vessels covered by a thin epithelial layer. Typically gills are

organi'ed into a series of plates and may be internal 0as in crabs and fish1 or

external to the body 0as in some amphibians1.

,ills are very efficient at removing oxygen from water# there is only 8936 the

amount of oxygen present in water as in the same volume of air. 2ater flows

over gills in one direction while blood flows in the opposite direction through

gill capillaries. This countercurrent flowmaximi'es oxygen transfer.
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookglossC.html#countercurrent%20flowhttp://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookglossC.html#countercurrent%20flow


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Countercurrent flow in a fish. -mages from Purves et al.$ (ife# The "cience ofiology$ /th !dition$ by "inauer Associates 0www.sinauer.com1 and 2& *reeman

0www.whfreeman.com1$ used with permission.

Tracheal Systems

:any terrestrial animals have their respiratory surfaces inside the body and

connected to the outside by a series of tubes.Tracheaeare these tubes that carry

air directly to cells for gas exchange. "piracles are openings at the body surface

that lead to tracheae that branch into smaller tubes known as tracheoles. ody

movements or contractions speed up the rate of diffusion of gases from

tracheae into body cells. &owever$ tracheae will not function well in animals

whose body is longer than 4 cm.
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;espiratory system in an insect.-mage from Purves et al.$ (ife# The "cience ofiology$ /th !dition$ by "inauer Associates 0www.sinauer.com1 and 2& *reeman


Lungs

(ungs are ingrowths of the body wall and connect to the outside by as series of

tubes and small openings. (ung breathing probably evolved about /66 million

years ago. (ungs are not entirely the sole property of vertebrates$ some

terrestrial snails have a gas exchange structures similar to those in frogs.
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(ungs in a bird 0top1 and amphibian 0bottom1.-mages from Purves et al.$ (ife# The"cience of iology$ /th !dition$ by "inauer Associates 0www.sinauer.com1 and 2&*reeman 0www.whfreeman.com1$ used with permission.

Respiratory System Principles| Back to Top
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8. :ovement of an oxygen%containing medium so it contacts a moist

membrane overlying blood vessels.

3.


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The human respiratory system.-mage from Purves et al.$ (ife# The "cience ofiology$ /th !dition$ by "inauer Associates 0www.sinauer.com1 and 2& *reeman


Air enters the body through the nose$ is warmed$ filtered$ and passed through

the nasal cavity. Air passes thepharynx0which has the epiglottisthat prevents

food from entering the trachea1.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 thebronchithat carry

air in and out of the lungs.
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The lungs and alveoli and their relationship to the diaphragm and capillaries.-mages from Purves et al.$ (ife# The "cience of iology$ /th !dition$ by "inauer

Associates 0www.sinauer.com1 and 2& *reeman 0www.whfreeman.com1$ used with

permission.

ronchi are reinforced to prevent their collapse and are lined with ciliatedepithelium and mucus%producing cells. ronchi branch into smaller and smaller

tubes known asbronchioles. ronchioles terminate in grape%like sac clusters

known as alveoli. Alveoli are surrounded by a network of thin%walled

capillaries. >nly about 6.3 ?m separate the alveoli from the capillaries due to

the extremely thin walls of both structures.

,as exchange across capillary and alveolus walls.-mage from Purves et al.$ (ife#The "cience of iology$ /th !dition$ by "inauer Associates 0www.sinauer.com1 and 2&

*reeman 0www.whfreeman.com1$ used with permission.

The lungs are large$ lobed$ paired organs in the chest 0also known as the

thoracic cavity1. Thin sheets of epithelium 0pleura1 separate the inside of the

chest cavity from the outer surface of the lungs. The bottom of the thoracic

cavity is formed by the diaphragm.
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@entilationis the mechanics of breathing in and out. 2hen you inhale$ muscles

in the chest wall contract$ lifting the ribs and pulling them$ outward. The

diaphragm at this time moves downward enlarging the chest cavity. ;educed

air pressure in the lungs causes air to enter the lungs. !xhaling reverses theses

steps.

-nhalation and exhalation.-mage from Purves et al.$ (ife# The "cience of iology$ /th!dition$ by "inauer Associates 0www.sinauer.com1 and 2& *reeman


!iseases of the Respiratory System| Back to Top

The condition of the airways and the pressure difference between the lungs and

atmosphere are important factors in the flow of air in and out of lungs. :any

diseases affect the condition of the airways.

Asthmanarrows the airways by causing an allergy%induced spasms of

surrounding muscles or by clogging the airways with mucus.

ronchitisis an inflammatory response that reduces airflow and is

caused by long%term exposure to irritants such as cigarette smoke$ airpollutants$ or allergens.

Cystic fibrosisis a genetic defect that causes excessive mucus

production that clogs the airways.

The "l#eoli and Gas Exchange| Back to Top
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xygen concentration in cells is low 0when leaving the lungs blood is 7

saturated with oxygen1$ so oxygen diffuses from the blood to the cells when it

reaches the capillaries.

!ffectiveness of various oxygen carrying molecules.-mage from Purves et al.$(ife# The "cience of iology$ /th !dition$ by "inauer Associates 0www.sinauer.com1 and

2& *reeman 0www.whfreeman.com1$ used with permission.

Carbon dioxide concentration in metabolically active cells is much greater than

in capillaries$ so carbon dioxide diffuses from the cells into the capillaries.

2ater in the blood combines with carbon dioxide to formbicarbonate. This

removes the carbon dioxide from the blood so diffusion of even more carbon

dioxide from the cells into the capillaries continues yet still manages to

DpackageD the carbon dioxide for eventual passage out of the body.
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$ontrol of Respiration| Back to Top

:uscular contraction and relaxation controls the rate of expansion and

constriction of the lungs. These muscles are stimulated by nerves that carry

messages from the part of the brain that controls breathing$ the medulla. Twosystems control breathing# an automatic response and a voluntary response.

oth are involved in holding your breath.

Although the automatic breathing regulation system allows you to breathe

while you sleep$ it sometimes malfunctions. Apneainvolves stoppage of

breathing for as long as 86 seconds$ in some individuals as often as =66 times

per night. This failure to respond to elevated blood levels of carbon dioxide

may result from viral infections of the brain$ tumors$ or it may develop

spontaneously. A malfunction of the breathing centers in newborns may result

in "-

the respiratory system and gas exchange.doc

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