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Chapter 32Gas Exchange and Transport

in Animals

Animals Have Gas-Exchange Surfaces

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32.1 Respiration involves several steps

Respiration - sequence of events that results in gas exchange between the body’s cells and the environment Ventilation - (i.e., breathing) includes inspiration (entrance of air

into the lungs) and expiration (exit of air from the lungs) External respiration - gas exchange between the air and the blood

within the lungs Blood transports oxygen from lungs to tissues

Internal respiration - gas exchange between blood and tissue fluid Body’s cells exchange gases with tissue fluid Blood then transports carbon dioxide to the lungs

For external respiration to be effective, gas-exchange region must be Moist Thin Large in relation to the size of the body

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Figure 32.1 Blood delivers oxygen to cells and transports carbon dioxide to the external respiration surfaces

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32.2 External respiration surfaces must be moist

More difficult for animals to obtain oxygen from water than from air Water fully saturated with air contains only a fraction of the amount of

oxygen that would be present in the same volume of air Hydras and planarians have a large surface area in comparison to

their size Makes it possible for most of their cells to exchange gases with the

environment The earthworm is able to use its body surface for respiration

because the capillaries come close to the surface Aquatic invertebrates (clams and crayfish) and aquatic vertebrates

(fish and tadpoles) have gills to extract oxygen from water Gills - finely divided, vascularized outgrowths of body surface or

pharynx Insects have a system of air tubes called tracheae through which

oxygen is delivered directly to the cells without entering the blood Terrestrial vertebrates usually have lungs, vascularized outgrowths

from the lower pharyngeal region The lungs of birds and mammals are elaborately subdivided into small

passageways and spaces, respectively 32-5

Figure 32.2A External respiration in a hydra

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Figure 32.2B An earthworm’s entire external surface functions in external respiration

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Figure 32.2C Fish have gills to assist external respiration

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Figure 32.2D Insects have a tracheal system that delivers oxygen directly to their cells

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Figure 32.2E Vertebrates have lungs with a large total external respiration surface

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32.3 Gills are an efficient gas-exchange surface in water

Animals with gills use various means of ventilation In molluscs (clam or squid) water is drawn into the mantle cavity

and passes through gills In crustaceans (crabs and shrimps) gills are located in thoracic

chambers covered by the exoskeleton In fish, ventilation is brought about by the combined

action of the mouth and gill covers, or opercula (sing., operculum) Bony fish’s gills are outward extensions of pharynx

Fish use countercurrent exchange to transfer oxygen from the surrounding water into their blood Two fluids flow in opposite directions and as blood gains oxygen,

it always encounters water having an even higher oxygen content

Prevents an equilibrium point from being reached, and about 80–90% of the initial dissolved oxygen in water is extracted

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Figure 32.3 Gills in bony fishes help carry out countercurrent exchange

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32.4 The tracheal system in insects permits direct gas exchange

Arthropods are coelomate animals, but the coelom is reduced Internal organs lie within a cavity called the hemocoel because it

contains hemolymph Hemolymph flows through the hemocoel, making circulation

inefficient Insects overcome the inefficiency by having a respiratory

system that consists of tracheae, tiny air tubes that take oxygen directly to the cells Tracheae branch into smaller tubules called tracheoles Tracheae expand and contract, drawing air in and out of the

system Tracheal system is an adaptation to breathing air, but some

insect larval stages and even some adult insects live in the water In these cases, tracheae do not receive air by way of spiracles Diffusion of oxygen across the body wall supplies tracheae with

oxygen 32-13

Figure 32.4 Tracheae in an insect

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32.5 The human respiratory system utilizes lungs as a gas-exchange surface

The human respiratory system includes all of the structures that conduct air in a continuous pathway to and from the lungs As air moves through nose, pharynx, the trachea, and bronchi to

lungs, it is filtered free of debris, warmed, and humidified Air and food passages cross in pharynx

Arrangement has advantage of letting you breathe through your mouth in case your nose is plugged up

Air passes from pharynx through glottis, an opening into the larynx or voice box At edges of glottis are vocal cords, bands of connective tissue that

produce sound when air is expelled past them Larynx and trachea remain open to receive air at all times

Trachea is held open by a series of cartilaginous rings When swallowing, the glottis is closed by a flap called the epiglottis

Trachea divides into two primary bronchi, which enter the lungs Branching continues, eventually forming a great number of smaller

passages called bronchioles 32-15

Figure 32.5 The human respiratory tract

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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES

32.6 Questions about tobacco, smoking, and health

Is there a safe way to smoke? No. All cigarettes can damage the body

Is cigarette smoking really addictive? Yes. Small amounts of nicotine make the smoker want to smoke more and

smokers usually suffer withdrawal symptoms when they stop Does smoking cause cancer?

Yes. Tobacco use accounts for about one-third of all cancer deaths in the United States

How does cigarette smoke affect the lungs? All smokers have a lower level of lung function than nonsmokers

Why do smokers have “smoker’s cough”? When a smoker inhales, the body tries to protect itself by producing mucus

and stimulating coughing If you smoke but do not inhale, is there any danger?

Yes. Wherever smoke touches living cells, it does harm Does cigarette smoking affect the heart?

Yes. Smoking increases the risk of heart disease, which is the number-one cause of death in the United States

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How does smoking affect pregnant women and their babies? Smoking during pregnancy is linked to a greater chance of miscarriage,

premature delivery, stillbirth, infant death, low birth weight, and sudden infant death syndrome

What are some of the short-term and long-term effects of smoking cigarettes? Short-term effects include shortness of breath and a nagging cough,

diminished ability to smell and taste, premature aging of the skin, and increased risk of sexual impotence in men

Long-term effects include many types of cancer, heart disease, aneurysms, bronchitis, emphysema, and stroke

What are the dangers of environmental tobacco smoke (ETS)? Children of smokers are more likely to suffer from asthma, pneumonia

or bronchitis, ear infections, coughing, wheezing, and increased mucus production

Are chewing tobacco and snuff safe alternatives to cigarette smoking? No. The juice from smokeless tobacco is absorbed directly through the

lining of the mouth, creating sores that often lead to mouth cancer

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Ventilation Precedes Transport

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32.7 Breathing brings air into and out of the lungs

Terrestrial vertebrates ventilate their lungs by moving air into and out of the respiratory tract Amphibians use positive pressure to force air into the respiratory

tract Reptiles have jointed ribs that can be raised to expand the lungs Mammals have a rib cage that is lifted up and out and a

diaphragm that is flattened Diaphragm is a horizontal muscle that divides the thoracic cavity

from the abdominal cavity Following inspiration (or inhalation), expiration (or exhalation)

occurs Birds use a one-way ventilation mechanism

Incoming air is carried past the lungs by a trachea, which takes it to a set of posterior air sacs

Air then passes forward through the lungs into a set of anterior air sacs where it is finally expelled

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Breathing in Humans

During inspiration in humans, the volume of the thoracic cavity and lungs is increased by muscle contractions that lower the diaphragm and raise the ribs Creates a negative pressure and air flows into the

lungs During expiration, rib and diaphragm muscles relax,

and air flows out as a result of increased pressure in the thoracic cavity and lungs

All terrestrial vertebrates, except birds, use a tidal ventilation mechanism Air moves in and out by the same route

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Figure 32.7A Inspiration

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Figure 32.7B Expiration

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Figure 32.7C Bellows at work

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Figure 32.7D Respiratory system in birds

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32.8 Our breathing rate can be modified

Rhythm of ventilation is controlled by a respiratory center in the medulla oblongata of the brain Normally, adults have a breathing rate of 12 to 20 ventilations

per minute Its activity can be influenced by nervous input and

chemical input Respiratory center is directly sensitive to levels of hydrogen ions

(H+) and when CO2 enters the blood, it releases H+ CO2 participates in regulating the breathing rate

Chemoreceptors in carotid bodies located in carotid arteries, and in aortic bodies, located in aorta, will stimulate the respiratory center during intense exercise

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Figure 32.8 Nervous control of breathing

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32.9 External and internal respiration require no energy

Diffusion governs movement of gases into and out of blood vessels in lungs and tissues External respiration - gas exchange in our lungs Internal respiration - gas exchange in the tissues

Amount of pressure each gas exerts is called the partial pressure (PO2 and PCO2) If PO2 or PCO2 differs across a membrane, they will diffuse from higher

to lower pressure Ventilation causes alveoli of lungs to have a higher PO2 and

a lower PCO2 than blood in pulmonary capillaries Accounts for exchange of gases in the lungs

Cellular respiration in cells causes the tissue fluid to have a lower PO2 and a higher PCO2 than the blood in the systemic capillaries Accounts for the exchange of gases in the tissues 32-28

Figure 32.9 External and internal respiration

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32.10 Hemoglobin is involved in transport of gases

External Respiration Oxygen entering pulmonary capillaries from alveoli combines with

hemoglobin (Hb) in red blood cells (RBC) to form oxyhemoglobin Each hemoglobin molecule contains four polypeptide chains, and each

chain is folded around an iron-containing group called heme

As blood enters the lungs, most of the CO2 in the pulmonary capillaries is carried as bicarbonate ions (HCO3

-) in the plasma

The reaction that releases CO2 from the bicarbonate ions occurs in red blood cells, where the enzyme carbonic anhydrase speeds the breakdown of carbonic acid

H+ + HCO3- H2CO3

H2O + CO2

hydrogen bicarbonate carbonic water carbon ion ion acid dioxide

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Internal Respiration Oxygen diffuses out of blood into tissues because the PO2 of

tissue fluid is lower than that of blood Lower PO2 is due to cells continuously using up oxygen in cellular

respiration Carbon dioxide enters blood from the tissues because the PCO2 of

tissue fluid is higher than that of blood After CO2 diffuses into the blood, it enters red blood cells, where a

small amount combines with protein portion of hemoglobin to form carbaminohemoglobin

Most of the CO2, however, is transported in the form of the bicarbonate ion (HCO3

-)

CO2 + H2O H2CO3 H+ + HCO3

-

carbon water carbonic hydrogen bicarbonatedioxide acid ion ion

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Figure 32.10 The iron atom of a heme group combines loosely with oxygen

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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES

32.11 Respiratory disorders have resulted from breathing 9/11 dust Dust particles at Ground Zero after the September 11, 2001, attack

contained asbestos, mercury from light bulbs, and lead from computers Respiratory disorders could occur in people who breathed this dust

Restrictive Pulmonary Disorders Lung capacity is reduced because the lungs have lost their elasticity

Obstructive Pulmonary Disorders Chronic bronchitis - airways are inflamed and filled with mucus Emphysema - chronic and incurable disorder in which the alveoli are

distended and their walls damaged Asthma - disease of the bronchi and bronchioles marked by wheezing,

breathlessness, and a cough with mucus Lung Cancer

First event appears to be thickening and callusing of cells lining bronchi Cilia are lost, making it impossible to prevent dust and dirt from settling

in lungs Atypical nuclei appear in the callused lining and a tumor consisting of

disordered cells with atypical nuclei occurs 32-33

Figure 32.11A People are now ill from breathing dust at Ground Zero

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Figure 32.11B A normal lung (with the heart in place) compared to the lungs of a heavy smoker

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Connecting the Concepts:Chapter 32

Assuming an adequate supply of O2, cells of most organisms continuously carry on cellular respiration and produce a comparable amount of CO2

Respiration is the exchange of gases between an organism and its external environment In small, thin, aquatic invertebrates, cells take care of their own

respiratory needs Complex invertebrates and vertebrates have respiratory organs, which

usually consist of gills in aquatic forms and lungs in terrestrial forms Ventilation is the active movement of water across a respiratory

surface (such as gills) or the movement of air into and out of lungs to increase the efficiency of gas exchange Respiratory organs of complex organisms work in conjunction with a

circulatory system to transport oxygen to cells and rid them of carbon dioxide

We are well aware that breathing polluted air is dangerous to our health The human respiratory system is impaired by the foreign particles and

molecules present in 9/11 dust and in cigarette smoke 32-36