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Respiration, Circulation, and Excretion

Respiration, Circulation, and Excretion

Gregg Epperson/Index Stock Imagery/PictureQuest

Coordination of the respiratoryand circulatory systems allowsblood to deliver much neededoxygen and nutrients to thehard-working cells of thisclimber.

Understandingthe Photo

What You’ll Learn■ You will identify the functions

of the respiratory system andexplain the mechanics ofbreathing.

■ You will describe the structureand function of the differenttypes of blood cells and tracethe pathway of blood circula-tion through the body.

■ You will describe the structureand function of the urinarysystem.

Why It’s ImportantWith a knowledge of how yourcirculatory, respiratory, and uri-nary systems function, you willunderstand how your cellsreceive, deliver, and removematerials to maintain yourbody’s homeostasis.

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37.1 THE RESPIRATORY SYSTEM 971

37.1SECTION PREVIEWObjectivesIdentify the structuresinvolved in external respiration.Contrast external and cellular respiration.Explain the mechanics of breathing.

Review Vocabularydiaphragm: sheet of

muscles beneath thelungs that separates thechest cavity from theabdominal cavity (p. 843)

New Vocabularytracheaalveoli

The Respiratory System

PhysicalScience

Connection

Elements, com-pounds, andmixtures ineveryday lifeThe atmosphere isa mixture of gases,liquids, and solids.The gases includenitrogen, oxygen,water vapor,argon, and carbondioxide. Smokeand wind-blowndust particles aresome of the solidsfound in air, andliquid waterdroplets are seenas clouds.

Organs Function

Respiratorysystem

Circulatorysystem

Urinarysystem

Make a Table As you read Chapter 37, complete the table by describing theorgans and functions of the respiratory, circulatory, and urinary systems.

Systems Make the following Foldable to help you organize information about the respiratory, circulatory, and urinary systems.

Fold one piece of paper lengthwise into thirds.

Fold the paper widthwise into fourths.

Unfold, lay the paper length-wise, and draw lines along the folds.

Label your table as shown.

STEP 1

STEP 3

STEP 2

STEP 4

Passageways and LungsYour respiratory system is made of a pair of lungs and a series of pas-

sageways, each one extending deeper into your body. These passagewaysinclude the nasal passages, the throat, the windpipe, and the bronchi.When you hear the term respiratory system, you probably think ofbreathing. However, breathing is just one of the functions that the res-piratory system carries out. Respiration, the process of gas exchange, isanother important function performed by the respiratory system.Respiration includes all of the mechanisms involved in getting oxygen tothe cells of your body and getting rid of carbon dioxide. Recall that cel-lular respiration also involves the formation of ATP within the cells.

The path air takesThe first step in the process of respiration involves taking air into your

body through your nose or mouth. Air flows into the pharynx, or throat,passes the epiglottis, and moves through the larynx. It then travels downthe windpipe, or trachea (TRAY kee uh), a tubelike passageway that leadsto two tubes, or bronchi (BRAHN ki) (singular, bronchus), which lead intothe lungs. When you swallow food, the epiglottis covers the entrance tothe trachea, which prevents food from getting into the air passages.

Cleaning dirty airThe air you breathe is far from

clean. An individual living in an urbanarea breathes in millions of particlesof foreign matter each day. To preventmost of this material from reachingthe lungs, the nasal cavity, trachea,and bronchi are lined with ciliatedcells that secrete mucus. The ciliaconstantly beat upward in the direc-tion of your throat, where foreignmaterial can be swallowed or expelledby coughing or sneezing. Follow thepassage of air through the respiratorysystem in Figure 37.1.

Alveoli: The place of gasexchange

Like the branches of a tree, eachbronchus branches into bronchioles,which in turn branch into numerousmicroscopic tubules that eventuallyopen into thousands of thin-walled sacscalled alveoli. Alveoli (al VEE uh li) arethe sacs of the lungs where oxygenand carbon dioxide are exchanged by

diffusion between the air and blood.The clusters of alveoli are surroundedby networks of tiny blood vessels, orcapillaries. Blood in these vessels hascome from the cells of the body andcontains wastes from cellular respira-tion. Diffusion of gases takes placeeasily because the wall of each alveo-lus, and the walls of each capillary, areonly one cell thick. External respira-tion involves the exchange of oxygenor carbon dioxide between the air inthe alveoli and the blood that circu-lates through the walls of the alveoli,and is shown in the inset portion ofFigure 37.1.

Blood transport of gasesOnce oxygen from the air diffuses

into the blood vessels surrounding thealveoli, it is pumped by the heart to thebody cells, where it is used for cellularrespiration. In an earlier chapter, youlearned that cellular respiration is theprocess by which cells use oxygen tobreak down glucose and release energyin the form of ATP. Carbon dioxide is

972 RESPIRATION, CIRCULATION, AND EXCRETION

alveoli from theLatin word alveolus, meaning“cavity” or “hol-low”; The alveoliare small air sacs of the lung.

Medullaoblongata

Pharynx

Bronchiole

Left lung

CO2-rich blood

O2 -rich blood

Alveoli

Alveolus

Capillary network

Nasal cavity

Epiglottis

Larynx

Esophagus

Trachea

Bronchus

Right lung

Diaphragm

Figure 37.1As air passes throughthe respiratory system,it travels through nar-rower and narrowerpassageways until itreaches the alveoli.Explain Interpret the functions of the respiratory system.

a waste product of this process. Thecarbon dioxide diffuses into the blood,which carries it back to the lungs.

As a result, the blood that comes tothe alveoli from the body’s cells is highin carbon dioxide and low in oxygen.Carbon dioxide from the body diffusesfrom the blood into the air spaces inthe alveoli. During exhalation, thiscarbon dioxide is removed from yourbody. At the same time, oxygen dif-fuses from the air in the alveoli intothe blood, making the blood rich inoxygen. Use the Problem-Solving Labon this page to find out more abouthow the composition of air changes asit passes through the lungs.

The Mechanics of Breathing

The action of your diaphragm andthe muscles between your ribs enableyou to breathe in and breathe out.Figure 37.2 shows how air is drawn inor forced out of the lungs as a result ofthe diaphragm’s position.

When contracting, the diaphragm flattens,enlarging the chest cavity and drawing airinto the lungs.

B

Position ofribs wheninhaling

Position of diaphragmwhen inhaling

Lung wheninhaling

Position ofribs whenexhaling

Position of diaphragm when exhaling

Lung whenexhaling

Figure 37.2The diaphragm is located beneath the lungs.Explain How does the contraction of thediaphragm affect air pressure in the lungs?

When relaxed, your diaphragm is posi-tioned in a dome shape beneath yourlungs, decreasing the volume of the chestcavity and forcing air out of the lungs.

A

Interpret DataHow do inhaled and exhaled air compare? Air is com-posed of a number of different gases. As a result of cellularrespiration, the percentages of some of the gases in air arealtered by the time air is exhaled from the body.

Solve the ProblemStudy the table below. It compares the relative percentages ofgases in inhaled and exhaled air.

Thinking Critically1. Interpret Data What information about cellular respira-

tion is conveyed by the data in the table?2. Sequence Trace the pathway that a molecule of nitrogen

follows when entering and leaving the lungs. (Note:Normally, nitrogen does enter the blood stream.)

3. Explain Why are carbon dioxide levels higher in air that is exhaled?

Comparison of Gases in Inhaled and Exhaled Air

Gas Inhaled Air Exhaled Air

Nitrogen 78.00% 78.00%

Oxygen 21.00% 16.54%

Carbon dioxide 0.03% 4.49%

Other gases 0.97% 0.97%

974 RESPIRATION, CIRCULATION, AND EXCRETIONJeff Greenberg/Visuals Unlimited

Understanding Main Ideas1. Describe the path an oxygen molecule takes as it

travels from your nose to a body cell. List eachstructure of the respiratory system through whichit passes.

2. Describe how air in the respiratory tract is cleanedbefore it reaches the lungs.

3. Contrast external respiration and cellular respiration.

4. Explain the process by which gases are exchangedin the lungs.

Thinking Critically5. During a temper tantrum, four-year-old Jamal

tries to hold his breath. His parents are afraid thathe will be harmed by this behavior. How willJamal be affected by holding his breath?

6. Sequence What is the sequence of muscleactions that takes place during inhalation andexhalation? For more help, refer to Sequencein the Skill Handbook.

SKILL REVIEWSKILL REVIEW

When you inhale, the musclesbetween your ribs contract and yourrib cage rises. At the same time, thediaphragm muscle contracts, becomesflattened, and moves lower in the chestcavity. These actions increase the spacein the chest cavity, which creates aslight vacuum. Air rushes into yourlungs because the air pressure outsideyour body is greater than the air pres-sure inside your lungs.

When you exhale, the muscles asso-ciated with the ribs relax, and your ribsdrop down in the chest cavity. Your

diaphragm relaxes, returning to itsresting position. The relaxation ofthese muscles decreases the volume ofthe chest cavity and forces most of theair out of the alveoli.

The alveoli in healthy lungs are elas-tic, they stretch as you inhale andreturn to their original size as youexhale. The alveoli still contain a smallamount of air after you exhale.Measure your breathing rate in theBioLab at the end of this chapter.

Control of RespirationBreathing is usually an involuntary

process. It is partially controlled by aninternal feedback mechanism thatinvolves signals being sent to themedulla oblongata about the chemistryof your blood. The medulla oblongatahelps maintain homeostasis. Itresponds to higher levels of carbondioxide in your blood by sending nervesignals to the rib muscles anddiaphragm. The nerve signals causethese muscles to contract, and youinhale. When breathing becomes morerapid, as during exercise, a more rapidexchange of gases between air andblood occurs.

Describe the rela-tionship between an internal feed-back mechanism and the rate ofrespiration.

Registered Nurse

If you want a fast-paced, hands-on career that puts your “people

skills” to work, consider becoming a registered nurse.

Skills for the JobNurses give care, support, and

advice as they help their patients get well or stay well. They may work in hospitals, doctors’ offices, schools, nursing homes, rehabilitation centers, or public healthagencies. Registered nurses (RNs) must complete a two-yearassociate degree program, a two- or three-year diplomaprogram, or a four-year bachelor’s degree. To becomelicensed, they must also pass a national test.

For more careers in related fields, visit

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37.2SECTION PREVIEWObjectivesDistinguish among thevarious components ofblood and among bloodgroups.Trace the route bloodtakes through the bodyand heart.Explain how heart rate iscontrolled.

Review Vocabularytissue: groups of cells that

work together to per-form a specific function(p. 210)

New Vocabularyplasmared blood cellhemoglobinwhite blood cellplateletantigenantibodyarterycapillaryveinatriumventriclevena cavaaortapulseblood pressure

37.2 THE CIRCULATORY SYSTEM 975

Your Blood: Fluid TransportYour blood is a tissue composed of fluid, cells, and fragments of cells.

Table 37.1 summarizes information about the components of humanblood. The fluid portion of blood is called plasma. Plasma is straw col-ored and makes up about 55 percent of the total volume of blood. Bloodcells—both red and white—and cell fragments are suspended in plasma.

Red blood cells: Oxygen carriersThe round, disk-shaped cells in

blood are red blood cells. Red bloodcells carry oxygen to body cells. Theymake up 44 percent of the total vol-ume of your blood, and are producedin the red bone marrow of your ribs,humerus, femur, sternum, and otherlong bones.

Red blood cells in humans havenuclei only during an early stage in eachcell’s development. The nucleus is lostbefore the cell enters the bloodstream.

The Circulatory System

Bob Daemmrich

Table 37.1 Blood Components

Components Characteristics

Red blood cells Transport oxygen and some carbon dioxide; lack a nucleus; contain hemoglobin

White blood cells Large; several different types; all contain nuclei; defend the body against disease

Platelets Cell fragments needed for blood clotting

Plasma Liquid; contains proteins; transports red and white blood cells, platelets, nutrients, enzymes,hormones, gases, and inorganic salts

Vital FunctionsUsing Prior Knowledge Youknow that when you scrape yourknee that blood will flow fromthe wound. What can you do tostop the bleeding? Applyingdirect pressure to the wound lim-its bleeding until the blood canclot. Forming clots is one func-tion of the blood. Blood also car-ries oxygen from your lungs andnutrients from your digestive sys-tem to your cells, then hauls awaycellular wastes. Together, yourblood, your heart, and a networkof blood vessels make up yourcirculatory system. Infer If the blood could not carryout its functions, how would this affect other cells in the body?

A blood clot is composed of a network offibers in which blood cells are trapped.

Red blood cells remain active in thebloodstream for about 120 days, thenthey break down and are removed aswaste. Old red blood cells are destroyedin your spleen, an organ of the lym-phatic system, and in your liver.

Oxygen in the bloodHow is oxygen carried by the

blood? Red blood cells like thoseshown in Figure 37.3 are equippedwith an iron-containing protein mole-cule called hemoglobin (HEE muhgloh bun). Oxygen becomes looselybound to the hemoglobin in bloodcells that have entered the lungs.

These oxygenated blood cells carryoxygen from the lungs to the body’scells. As blood passes through body tis-sues with low oxygen concentrations,oxygen is released from the hemoglo-bin and diffuses into the tissues.

Carbon dioxide in the bloodHemoglobin carries some carbon

dioxide as well as oxygen. You havealready learned that, once biologicalwork has been done in a cell, wastesin the form of carbon dioxide diffuseinto the blood and are carried in thebloodstream to the lungs. About 70 percent of this carbon dioxidecombines with water in the bloodplasma to form bicarbonate. Theremaining 30 percent travels back tothe lungs dissolved in the plasma orattached to hemoglobin moleculesthat have already released their oxy-gen into the tissues.

White blood cells: Infection fighters

White blood cells, shown inFigure 37.4, play a major role in protecting your body from foreignsubstances and from microscopicorganisms that cause disease. Theymake up only one percent of the totalvolume of your blood.

976 RESPIRATION, CIRCULATION, AND EXCRETION(t)Biophoto Associates/Science Source/Photo Researchers, (b)Ed Reschke/Peter Arnold, Inc.

Figure 37.3Red blood cells are disk-shaped cells that carryoxygen to tissue cells through thin-walled capillaries.

Figure 37.4Compared with redblood cells, whiteblood cells are larger insize and far fewer innumber. White bloodcells have a nucleus;mature red blood cellsdo not have a nucleus.

Side view

Top view

Stained LM Magnification: 250�

LM Magnification: 200�

Red blood cell

White blood cells

2.0 micrometers

7.5 micrometers

Blood clottingThink about what happens when

you cut yourself. If the cut is slight,you usually bleed for a short while,until the blood clots. That’s because,in addition to red and white bloodcells, your blood also contains smallcell fragments called platelets, whichhelp blood clot after an injury, asshown in Figure 37.5. Platelets helplink together a sticky network of pro-tein fibers called fibrin, which forms aweb over the wound that traps escap-ing blood cells. Eventually, a dry,leathery scab forms. Platelets are pro-duced from cells in bone marrow andhave a short life span. They areremoved from the blood by the spleenand liver after only about one week.

ABO Blood GroupsIf a person is injured so severely

that a massive amount of blood is lost,a transfusion of blood from a secondperson may be necessary. Wheneverblood is transfused from one personto another, it is important to know towhich blood group each personbelongs. You have already learnedabout the four human blood groups—A, B, AB, and O. You inherited thecharacteristics of one of these bloodgroups from your parents. Some-times, the term blood type is used todescribe the blood group to which aperson belongs. If your blood fallsinto group O, for example, you aresaid to have type O blood.

Blood surface antigens determine blood group

Differences in blood groups are dueto the presence or absence of proteins,called antigens, on the membranes ofred blood cells. Antigens are sub-stances that stimulate an immuneresponse in the body. As you’ll learn in a later chapter, an immune response

defends the body against foreign pro-teins. The letters A and B stand forthe types of blood surface antigensfound on human red blood cells.

Blood plasma contains proteins,called antibodies (AN tih bahd eez),that are shaped to correspond withthe different blood surface antigens.The antibody in the blood plasmareacts with its matching antigen onred blood cells if they are broughtinto contact with one another. Thisreaction results in clumped bloodcells that can no longer function.Each blood group contains antibodiesfor the blood surface antigens foundonly in the other blood groups—notfor antigens found on its own redblood cells.

For example, if you have type Ablood, you have the A antigen on yourred blood cells and the anti-B antibodyin your plasma. If you had anti-A anti-bodies, they would react with yourown type A red blood cells. Whatwould happen if you had type A bloodand anti-A was added to it by way of a transfusion of type B blood?

Meckes/Ottawa/Photo Researchers


Figure 37.5The whitish, globularstructures shown adher-ing to red blood cellsare platelets. DescribeWhat is the functionof platelets?

Color-enhanced SEM Magnification: 120�

An antigen-antibody reaction wouldoccur, resulting in clumped blood cellslike those shown in Figure 37.6B.Clumped blood cells cannot carryoxygen or nutrients to body cells.Similarly, if you have type B blood,you have the B antigen on your redblood cells and the anti-A antibody inyour blood plasma. Figure 37.6Cillustrates the antigens and antibodiespresent in each blood group.

Rh factorAnother characteristic of red blood

cells involves the presence or absenceof an antigen called Rh, or Rhesusfactor. Rh factor is an inherited

characteristic. People are Rh positive(Rh�) if they have the Rh antigenfactor on their red blood cells. Theyare Rh negative (Rh�) if they don’t.

Rh factor can cause complications insome pregnancies. The problem beginswhen an Rh� mother becomes preg-nant with an Rh� baby. At birth, theRh� baby’s blood mixes with the Rh�

blood of the mother, as Figure 37.7Aillustrates. Upon exposure to the baby’sRh� antigen factor, the mother willmake anti-Rh� antibodies like thoseshown in Figure 37.7B. If the motherbecomes pregnant again, these anti-bodies can cross the placenta. If the new fetus is Rh�, the anti-Rh�

(l)John Forsythe/Visuals Unlimited, (r)George W. Wilder/Visuals Unlimited

Anti-B antibody

Anti-B antibody

No antibodies

No antigens

Anti-A antibody

Anti-A antibody

Antigen A

Antigen A

Antigen B

Antigen B

Blood Type A Blood Type B

Blood Type AB Blood Type O

Red blood cell

Red blood cell Red blood cell

Red bloodcell

Figure 37.6Blood contains both antigens and antibodies.

Normal blood is shownhere. The plasma inyour blood containsantibodies that donot react with theantigens on yourown red blood cells.

A


The clumped blood illustrates anantibody-antigen reaction that couldoccur with an incorrect transfusion.

B

978


The four types ofblood groups havedifferent antigensand antibodies.

C

antibodies from the mother will destroyred blood cells in the fetus, as shown inFigure 37.7C.

Prevention of this problem is possi-ble. When the Rh� fetus is 28 weeksold, and again shortly after the Rh�

baby is born, the Rh� mother is givena substance that prevents the produc-tion of Rh antibodies in her blood. Asa result, the next fetus will not be indanger.

Your Blood Vessels:Pathways of Circulation

Because blood is fluid, it must bechanneled through blood vessels likethose shown in Figure 37.8. Thethree main types of blood vessels arearteries, capillaries, and veins. Each isdifferent in structure and function.

Arteries are large, thick-walled,muscular, elastic blood vessels thatcarry blood away from the heart.

Figure 37.7If a baby inher-its Rh+ bloodfrom the fatherand the motheris Rh–, problemscan develop ifthe blood cellsof mother andbaby mix duringbirth.

Placenta

First pregnancy

Anti-Rh�

antibodies

Possiblesubsequentpregnancies

Rh�

antigens

Right pulmonary artery (lung)

Right pulmonary veins (lung)

Vena cava

Systemic veins

Aorta

Left pulmonaryartery (lung)

Capillariesin lungs

Heart

Systemicarteries

Left pulmonary veins (lung)

Figure 37.8Arteries carry blood awayfrom the heart, whereasveins carry blood towardthe heart. Capillaries forman extensive web in thetissues.


Mother is exposed to Rhantigens at the birth ofher Rh� baby.

A Mother makes anti-Rh�

antibodies.

B During the mother’snext pregnancy, Rhantibodies can cross theplacenta and endangerthe fetus.

C

The blood that they carry is undergreat pressure. As the heart contracts,it pushes blood through the arteries.Each artery’s elastic walls expandslightly. As the heart relaxes, theartery shrinks a bit, which also helpspush the blood forward. As a result,blood surges through the arteries inpulses that correspond with therhythm of the heartbeat.

After the arteries branch off fromthe heart, they divide into smallerarteries that, in turn, divide into evensmaller vessels called arterioles.Arterioles (ar TEER ee ohlz) enter tis-sues, where they branch into the small-est blood vessels, the capillaries.Capillaries (KA puh ler eez) are micro-scopic blood vessels with walls that areonly one cell thick. These vessels areso tiny that red blood cells must movethrough them in single file. Capillariesform a dense network that reaches vir-tually every cell in the body. Thin cap-illary walls enable nutrients and gasesto diffuse easily between blood cellsand surrounding tissue cells.

As blood leaves the tissues, the cap-illaries join to form slightly larger ves-sels called venules. The venules mergeto form veins, the large blood vessels

that carry blood from the tissues backtoward the heart. Blood in veins is notunder pressure as great as that in thearteries. In some veins, especially thosein your arms and legs, blood travelsuphill against gravity. These veins areequipped with valves that preventblood from flowing backward. Figure37.9 shows how these valves function.When your skeletal muscles contract,the top valves open, and blood isforced toward the heart. When theskeletal muscles relax, the top valvesclose to prevent blood from flowingbackward, away from the heart.

Explain why someveins have valves.

Your Heart: The Vital Pump

The thousands of blood vessels inyour body would be of little use ifthere were not a way to move bloodthrough them. The main function ofthe heart is to keep blood movingconstantly throughout the body. Welladapted for its job, the heart is a largeorgan made of cardiac muscle cellsthat are rich in energy-producingmitochondria.

All mammalian hearts, includingyours, have four chambers. The twoupper chambers of the heart are theatria. The two lower chambers arethe ventricles. The walls of eachatrium are thinner and less muscularthan those of each ventricle. As youwill see, the ventricles perform morework than the atria, a factor that helpsexplain the thickness of their muscles.Each atrium pumps blood into thecorresponding ventricle. The leftventricle pumps blood to the entirebody, so its muscles are thicker thanthose of the right ventricle, whichpumps blood to the lungs. As a result,your heart is somewhat lopsided.


vena cava fromthe Latin wordsvena, meaning“vein,” and cava,meaning “empty”;Each vena cavaempties blood intothe heart.

To heart

Valveopen

Vein

Valveclosed

Contractedskeletalmuscles

Relaxedskeletalmuscles

Blood pushedup by musclesbelow

Figure 37.9Veins contain one-wayvalves that work in con-junction with skeletalmuscles.

Blood’s path through the heartBlood enters the heart through the

atria and leaves it through the ventri-cles. Both atria fill up with blood at the same time. The right atriumreceives oxygen-poor blood from the head and body through two largeveins called the venae cavae (vee nee • KAY vee) (singular, vena cava).The left atrium receives oxygen-richblood from the lungs through fourpulmonary veins. These veins are theonly veins that carry blood rich inoxygen. After they have filled withblood, the two atria then contract,pushing the blood down into the twoventricles.

After the ventricles have filled withblood, they contract simultaneously.When the right ventricle contracts, itpushes the oxygen-poor blood fromthe right ventricle out of the heartand toward the lungs through thepulmonary arteries. These arteries arethe only arteries that carry blood poorin oxygen. At the same time, the leftventricle forcefully pushes oxygen-rich blood from the left ventricle outof the heart through the aorta to thearteries of the body. The aorta is thelargest blood vessel in the body. SeeFigure 37.10 on the next page tolearn how a drop of blood movesthrough the heart.

Heartbeat regulationEach time the heart beats, a surge

of blood flows from the left ventricleinto the aorta and then into the arter-ies. Because the radial artery in thearm and carotid arteries near the jaware fairly close to the surface of thebody, the surge of blood can be felt asit moves through them. This surge ofblood through an artery is called apulse. Find out more about how thepulse is used to measure heart rate byconducting the MiniLab on this page.

Jeff Greenberg/Visuals Unlimited


ExperimentChecking Your Pulse The heart speeds up when the blood volume reaching your right atrium increases. It also speeds up when you exercise. The number of heartbeats per minute is your heart rate, which can be measured by taking your pulse.

Procedure! Copy the data table.@ Have a classmate take your resting

pulse for 60 seconds while you are sitting at your lab table or desk. Use the photo above as a guide to finding your radial pulse.

# Record your pulse in the table.$ Repeat steps 2 and 3 four more times, then calculate your

average resting pulse rate. Switch roles and take yourclassmate’s resting pulse.

% Exercise by walking in place for one minute.^ Have your classmate take your pulse for 60 seconds imme-

diately after exercising. Record the value in the data table.& Repeat steps 5 and 6 four more times, then calculate your

average pulse after exercise. Switch roles again with yourclassmate.

Analysis1. Explain Why is your pulse a means of indirectly measur-

ing heart rate?2. Describe Use values from your data table to describe the

changes that occur to your heart rate when exercising.3. Use Numbers Suppose the amount of blood pumped by

your left ventricle each time it contracts is 70 mL. Calculateyour cardiac output (70 mL � heart rate per minute) whileat rest and just after exercise.

Data Table

Heart Rate (beats per minute)

Trial Resting After Exercise

1

2

3

4

5

Total

Average

Your HeartFigure 37.10Your heart is about 12 cm by 8 cm—roughly the size of your fist. It lies in your chestcavity, just behind the breastbone and between the lungs, and is essentially a largemuscle completely under involuntary control. Critical Thinking The cells in hearttissue receive oxygen and nutrients from a group of blood vessels locatedon the wall of the heart. How would the function of the heart be affectedif bloodflow in these vessels was reduced?


RV

RALV

LA

Superiorvena cava

Pulmonaryartery

Pulmonaryvein

Capillaries

Right lung Inferiorvena cava

Left lung

Aorta

The passage of blood If you were to tracethe path of a drop of blood through the heart,you could begin with blood coming back fromthe body through a vena cava. The drop travelsfirst into the right atrium, then into the rightventricle, and then through a pulmonary arteryto one of the lungs. In the lungs, the blood dropsoff its carbon dioxide and picks up oxygen. Thenit moves through a pulmonary vein to the leftatrium, into the left ventricle, and finally out tothe body through the aorta, eventually returningonce more to the heart.

A

Heart valvesBetween the atria andventricles are one-wayvalves that keep bloodfrom flowing backinto the atria. Sets ofvalves also lie betweenthe ventricles and thearteries that leave theheart.

B

Superiorvena cava

Right lung

Right atrium

Right ventricle

Right coronaryartery

Arch of aorta

Pulmonary trunk

Left atrium

Left ventricle

Rib (cut)

Left Lung

Cut edge of pericardium

Left coronary artery

Diaphragm

Pericardium The heart is enclosed in aprotective membrane called the pericardium.

C

Science Photo Library/Photo Researchers

The heart rate is set by the pace-maker, a bundle of nerve cells locatedat the top of the right atrium. Thispacemaker generates an electricalimpulse that spreads over both atria.The impulse signals the two atria tocontract at almost the same time. Theimpulse also triggers a second set ofcells at the base of the right atrium tosend the same electrical impulse overthe ventricles, causing them to con-tract. These electrical signals can bemeasured and recorded by a machinecalled an electrocardiograph. Thisrecording, shown in Figure 37.11, iscalled an electrocardiogram (ECG).

The ECG is an important tool usedin diagnosing abnormal heart rhythmsor patterns. Each peak or valley in theECG tracing represents a particularelectrical activity that takes place dur-ing a heartbeat. You can learn howECG tracings are analyzed by carry-ing out the Problem-Solving Lab onthis page.

Andrew McClenaghan/Science Photo Library/Photo Researchers

T P

R

Ventriculardepolarization

Ventricularrepolarization

Atrialdepolarization

QS

T P

R

QS

0 0.1 0.2Seconds

Volta

ge (m

V)

0.3

1.0

0.5

0

-0.5

Figure 37.11The heart’s pacemaker generates electricalsignals that can be recorded on an ECG trac-ing. The sinoatrial node (pacemaker) causesboth atria to contract simultaneously 70–80impulses per minute. The atrioventricularnode passes the impulse to the walls of theventricles, which contract simultaneously.

Sinoatrial node(Pacemaker)

Atrioventricularnode


Analyze Information How are electrocardiograms analyzed? The electrical signalsthat regulate the pattern of heartmuscle contraction and relaxationcan be measured and recorded onan electrocardiograph.

Solve the ProblemThe electrocardiogram (ECG) in Figure 37.11 is a tracing from a normal heart. The red, inked line is marked with letters that can be used to identify electricalimpulses that occur during the heartbeat, such as P–Q and QRS.Segment P–Q represents the electrical charge that causes theatria to contract. Segment Q–T records the electrical chargethat causes the ventricles to contract and repolarize. The blue,vertical lines of the graph paper represent units of time. Thedistance between heavy graph lines is equal to 0.1 seconds. The distance between light lines is equal to 0.02 seconds.

Thinking Critically1. Analyze How long does it take for the electrical signal to

travel through the atria? Through the ventricle?2. Infer How would a physician interpret an ECG if the dis-

tances between T and P were much closer?

Electrocardiograph

Understanding Main Ideas1. Summarize the distinguishing features and func-

tions of each of the four components of blood:plasma, platelets, and red and white blood cells.

2. Compare and contrast an artery and a vein.

3. Outline the path taken by a red blood cell as itpasses from the left atrium to the right ventricleof the heart.

4. Identify and interpret the functions of the circulatory system.

Thinking Critically5. The level of carbon dioxide in the blood affects

breathing rate. How would you expect high levelsof carbon dioxide to affect the heart rate?

6. Get the Big Picture Compare how the nervous,respiratory, and circulatory systems interrelate toprovide life support to body cells. How wouldhomeostasis be affected if one of these systemscould not function? For more help, refer to Getthe Big Picture in the Skill Handbook.



Figure 37.12Blood pressure rises andfalls with each heartbeat. Pressure isexerted on all vesselsthroughout the body.However, blood vesselsnear the left ventricleare subjected to higherpressure than vesselsthat are farther away.Blood pressure usuallyis measured in theartery of the upper arm.

Syst

emic

blo

od p

ress

ure

(mm

Hg)

100

80

60

40

20

0

120

Distance from left ventricle

Blood Pressure

Aor

ta

Systolic pressure

Diastolic pressure

Larg

e ar

terie

s

Smal

l art

erie

s

Art

erio

les Ca

pilla

ries

Venu

les

Smal

l vei

ns

Larg

e ve

ins

Vena

cav

ae

Rubbercuff

Mercurycolumn

Air controlvalve

Bulb

Blood pressureA pulse beat represents the pres-

sure that blood exerts as it pushesagainst the walls of an artery. Blood pressure is the force that theblood exerts on the blood vessels. AsFigure 37.12 shows, blood pressurerises and falls as the heart contractsand then relaxes.

Blood pressure rises sharply whenthe ventricles contract, pushing bloodthrough the arteries. The high pressureis called systolic pressure. Blood pres-sure then drops dramatically as the ven-tricles relax. The lowest pressure occursjust before the ventricles contract againand is called diastolic pressure.

Control of the heartWhereas the pacemaker controls

the heartbeat, a portion of the braincalled the medulla oblongata regu-lates the rate of the pacemaker, speed-ing or slowing its nerve impulses. Ifthe heart beats too fast, sensory cellsin arteries near the heart becomestretched. Via the nervous system,these cells send a signal to themedulla oblongata, which in turnsends signals that slow the pacemaker.If the heart slows down too much,blood pressure in the arteries drops,signalling the medulla oblongata tospeed up the pacemaker and increasethe heart rate.



37.3SECTION PREVIEWObjectivesDescribe the structuresand functions of the urinary system.Explain the kidneys’ role inmaintaining homeostasis.

Review Vocabularyamino acids: basic building

blocks of proteins (p. 161)

New Vocabularykidneyureterurinary bladdernephronurineurethra

37.3 THE URINARY SYSTEM 985

Kidneys: Structure and Function

The urinary system is made up of twokidneys, a pair of ureters, the urinarybladder, and the urethra, which you cansee in Figure 37.13. The kidneys filterthe blood to remove wastes from it, thusmaintaining the homeostasis of body flu-ids. Your kidneys are located just abovethe waist, behind the stomach. One kid-ney lies on each side of the spine, par-tially surrounded by ribs. Each kidney isconnected to a tube called a ureter,which leads to the urinary bladder. Theurinary bladder is a smooth muscle bagthat stores a solution of wastes.

Nephron: The unit of the kidneyEach kidney is made up of about one

million tiny filters. A filter is a devicethat removes impurities from a solution.

The Urinary System

Clinical Radiology Dept./Salisbury District Hospital/Science Photo Library/Photo Researchers

Figure 37.13The paired kidneys arereddish-colored organsthat resemble kidneybeans in shape.

Vena cava

Renal artery

Renal vein

Urinary bladder

Aorta

Kidney

Ureters

Urethra

Waste RemovalUsing an Analogy Sorting yourCDs is a process similar to how thekidneys filter the blood. Some CDsyou know you want to keep. Thoseare never even removed from therack. Of the remaining CDs, someyou will end up keeping, while oth-ers you may give away or sell.When blood enters the kidney,proteins and blood cells remain inthe blood. Other substances, suchas water and ions, are removedfrom the blood by a filter but maybe reabsorbed later. Waste materialis not reabsorbed and is excreted inthe urine.Explain Why is it important thatwaste material be excreted from the body?

Left and right ureters lead to the urinarybladder, as seen in a colorized X ray ofthe human urinary system.

Each filtering unit of the kidney is called a nephron. A nephron isshown in Figure 37.14.

Blood entering a nephron carrieswastes produced by body cells. Asblood enters the nephron, it is underhigh pressure and immediately flowsinto a bed of capillaries called theglomerulus. Because of the pressure,water, glucose, vitamins, amino acids,protein waste products (called urea),salts, and ions from the blood pass out

of the capillaries into a part of thenephron called the Bowman’s capsule.Blood cells and most proteins are toolarge to pass through the walls of acapillary, so these components staywithin the blood vessels.

The liquid forced into theBowman’s capsule passes through anarrow, U-shaped tubule. As the liq-uid moves along the tubule, most ofthe ions and water, and all of the glu-cose and amino acids, are reabsorbedinto the bloodstream. This reabsorp-tion of substances is the process bywhich the body’s water is conservedand homeostasis is maintained. Smallmolecules, including water, move backinto the capillaries by diffusion. Othermolecules and ions move back into thecapillaries by active transport.

Explain how mole-cules move across capillaries.

The formation of urineThe liquid that remains in the

tubules—composed of waste moleculesand excess water and ions—is urine.

nephron from the Greek wordnephros, meaning“kidney”; Anephron is a func-tional unit of akidney.

Figure 37.14The kidneys filter wastes fromthe blood. Explain How doesblood enter and leave thekidneys?

Glomerulus

Fromrenalartery

Renalartery

To renalvein

Renal vein

Ureter

Tubule

Capillaries

To ureter

Nephron Bowman’s capsule

Artery

Vein

Blood cells, water,salts, nutrients, urea

Bowman's capsule

Capillaries

UreaWater

WaterSalts

Salts

Nutrients

Nutrients

Blood cells, water, salts, nutrients

Tubule

Urine: Urea,excess water,

salts

Collecting duct to ureter

Figure 37.15Filtration and reabsorp-tion take place in thenephron.



The production of urine is shown inFigure 37.15. You produce about 2 Lof urine a day. This waste fluid flowsout of the kidneys, through the ureter,and into the urinary bladder, where itmay be stored. Urine passes from theurinary bladder out of the bodythrough a tube called the urethra(yoo REE thruh).

The Urinary System and Homeostasis

The major waste products of cellsare nitrogenous wastes, which comefrom the breakdown of proteins.These wastes include ammonia andurea. Both compounds are toxic toyour body and, therefore, must beremoved from the blood regularly.

In addition to removing thesewastes, the kidneys control the level ofsodium in blood by removing andreabsorbing sodium ions. This helpscontrol the osmotic pressure of theblood. The kidneys also regulate thepH of blood by filtering out hydrogenions and allowing bicarbonate to bereabsorbed back into the blood.Glucose is a sugar that is not usuallyfiltered out of the blood by the kid-neys. Individuals who have the diseaseknown as diabetes have excess levels ofglucose in their blood. The MiniLabon this page shows how urine is usedto test for diabetes.

Understanding Main Ideas 1. Identify the organs that make up the urinary

system and interpret the function of each.2. What is the function of a nephron in the kidney?

Describe what happens in the glomerulus,Bowman’s capsule, and U-shaped tubule.

3. Identify the major components of urine, andexplain why it is considered a waste fluid.

4. What is the kidney’s role in maintaining homeostasis in the body?

Think Critically5. During a routine physical, a urine test indicates

the presence of proteins in the patient’s urine.Explain what this could indicate about thepatient’s health.

6. Sequence Trace the sequence of urinary wastefrom a cell to the outside of the body. For morehelp, refer to Sequence in the Skill Handbook.



ExperimentTesting Simulated Urine for Glucose Glucose is normallynot present in the urine. When the concentration of glucosebecomes too high in the blood, as happens with diabetes, glu-cose is excreted in urine.

Procedure! Copy the data

table.@ Using a grease

pencil, draw twocircles on a glassslide. Mark onecircle N, theother A.

# Use a cleandropper to addtwo drops of simulated “normal urine” to circle N.

$ Use a clean dropper to add two drops of simulated“abnormal urine” to the circle marked A.

% Hold a small strip of glucose test paper in a forceps andtouch it to the liquid in the drop labeled N. Remove it,wait 30 seconds, and record the color. A green color meansglucose is present. Use a new strip of glucose test paper totest drop A and record the color.

^ Test several simulated “unknown urine” samples for thepresence of glucose. Use a clean slide for each test.

Analysis1. Analyze Which of the “unknown” samples could be

from a person who has diabetes?2. Explain Which part of the test procedure could be

considered your control?

Data Table

Simulated Color of GlucoseUrine Sample Test Paper Present?

Normal (N)

Abnormal (A)

Unknown X

Unknown Y

Unknown Z



Before You BeginThe exchange of oxygenand carbon dioxide be-tween the body and theatmosphere is external respiration. The amount of air inhaled and exhaledeach minute during exter-nal respiration can bemeasured using a clinicalmachine called a spirome-ter. It also can be measured,although less accurately,using a balloon. In this labyou will calculate the totalvolume of air inhaled andexhaled each minute. Thisis done by finding thetidal volume, the volumeof air in each breath, andmultiplying it by the num-ber of breaths per minute.

Measuring Respiration

ProblemHow can you measure respiratory rate and estimate tidal volume?

ObjectivesIn this BioLab, you will:■ Measure resting breathing rate.■ Estimate tidal volume by exhaling into a balloon.■ Calculate the amount of air inhaled per minute.

Materialsround balloon clock or watch with string (1 m) second handmetric ruler

Safety PrecautionsCAUTION: Always use laboratory materials appropriately.

Skill HandbookIf you need help with this lab, refer to the Skill Handbook.

Part A: Breathing Rate at Rest1. Copy Data Table 1.2. Have your partner count the number of times you inhale

in 30 s. Repeat this step two more times.3. Calculate the average number of breaths. Multiply the

result by two to get the average resting breathing rate inbreaths per minute.

Trial

1

2

3

Average number breaths

Breaths per minute

Inhalations in 30 s

Resting Breathing Rate

Data Table 1

PROCEDUREPROCEDURE

PREPARATIONPREPARATION

Matt Meadows

4�r3

3


mL/min

L/min

Amount of Air Inhaled

Data Table 3

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

1. Make Comparisons Compare your averagenumber of breaths per minute and tidal vol-ume per minute with those of other students.

2. Think Critically An average adult inhales6000 mL of air per minute. Compare yourestimated average volume of air with this figure. What factors could account for any differences?

3. Make Predictions Predict what would happento your resting breathing rate after exercise.

4. List reasons that explain whythere are differences between your results andthose of other students. What changes could youmake to this experiment to obtain more accurateresults?

ERROR ANALYSIS

Apply Concepts The largest amount of airthat can be exhaled is called vital capacity.Determine your estimated average vitalcapacity by following a procedure similar tothe one you used to determine average tidalvolume.

Web Links To find out more aboutrespiratory volumes, visit

Part B: Estimating Tidal Volume1. Copy Data Table 2.2. Take a regular breath and exhale normally into the

balloon. Pinch the balloon closed.3. Have a partner fit the string around the balloon at

the widest part.4. Measure the length of the string, in centimeters,

around the circumference of the balloon. Recordthis measurement.

5. Repeat steps 2–4 four more times.6. Calculate the average circumference of the five

measurements.7. Calculate the average radius of the balloon by dividing the average

circumference by 2� (� � 3.14).8. Calculate the average tidal volume using the formula for determining

the volume of a sphere. Use the average balloon radius for r and 3.14for �. (Volume of a sphere � )

9. Your calculated volume will be in cubic centimeters: 1 cm3 � 1 mL.

Part C: Amount of Air Inhaled1. Copy Data Table 3.2. Multiply the average tidal volume by the average number of breaths

per minute to calculate the amount of air you inhale per minute.3. Divide the number of milliliters of air by 1000 to get the number of

liters of air you inhale per minute.

Trial

1

2

3

4

5

Average circumference

Average radius

Average tidal volume

String Measurement

Tidal Volume

Data Table 2

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The ability to replace a diseased heart, liver, kid-ney, pancreas, or other organ from a human

donor has been an important advancement formedical science. Organs suitable for transplantingare scarce, and there are thousands of transplantpatients waiting for them. Transplant recipientsinclude children born with malformed hearts ordigestive systems, patients suffering from severeliver or heart disease, burn victims in desperateneed of skin grafts, or people whose kidneys havestopped functioning.

The waiting list A patient who is a good can-didate for a transplant is placed on a waiting list.A national computer database keeps track of eachpatient’s blood and tissue type, organ size, andother medical factors. When an organ becomesavailable, the computer produces a list of all thepatients for whom the organ is medically suit-able. Patients are ranked according to the sever-ity of their illness, the length of time they havebeen waiting, and the distance between thedonor and the transplant hospital.

Perspectives A donor organ must be trans-planted within hours. Deciding who shouldreceive an organ involves questions of medicalurgency and logistics. Although over 20 000 suc-cessful organ transplants were performed in theUnited States in the year 2000, almost 80 000people remained on the waiting list. One of themost important issues concerning organ trans-plantation today is the fact that there are morepeople awaiting organs than there are donororgans available.

Revising policies In 1998, the Department ofHealth and Human Services asked the nationalorganization that coordinates the matching oforgans with patients to revise their policies andmake organs available to patients based on med-ical need regardless of location. If medically suit-able recipients are selected based on geographic

Finding TransplantDonors

Analyze the Issue Research and analyze the med-ical and ethical considerations involved in organdonation and transplantation. What is your opinionon this issue? Organize a class discussion to sharewhat you learned.

To find out more about organ transplants, visit

Michelle Del Guercio/Custom Medical Stock Photo

Recovering transplant patient

bdol.glencoe.com/biology_society

location, a seriously ill patient who lives far froma large population center might have to waitlonger than a patient who lives in a big city.However, if the most seriously ill patient is so faraway that the transplant cannot be completedwithin the time limit, another patient must beselected. Policies regarding organ distributionand allocation are being revised to provide a setof medically objective measures by which recipi-ents can be designated.

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Section 37.1

Section 37.2

Section 37.3

Vocabularyalveoli (p. 972)trachea (p. 971)

Vocabularyantibody (p. 977)antigen (p. 977)aorta (p. 981)artery (p. 979)atrium (p. 980)blood pressure (p. 984)capillary (p. 980)hemoglobin (p. 976)plasma (p. 975)platelet (p. 977)pulse (p. 981)red blood cell (p. 975)vein (p. 980)vena cava (p. 981)ventricle (p. 980)white blood cell

(p. 976)

Vocabularykidney (p. 985)nephron (p. 986)ureter (p. 985)urethra (p. 987)urinary bladder

(p. 985)urine (p. 986)

The CirculatorySystem

The UrinarySystem

STUDY GUIDESTUDY GUIDE

CHAPTER 37 ASSESSMENT 991(c)Meckes/Ottawa/Photo Researchers, (b)Clinical Radiology Dept./Salisbury District Hospital/Science Photo Library/Photo Researchers

To help you review therespiratory system, use the Organiza-tional Study Fold on page 971.

The RespiratorySystem

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Key Concepts■ External respiration involves taking in air

through the passageways of the respiratorysystem and exchanging gases in the alveoliof the lungs.

■ Breathing involves contraction of the dia-phragm, the rush of air into the lungs,relaxation of the diaphragm, and air beingpushed out of the lungs.

■ Breathing is partially controlled by thechemistry of the blood.

Key Concepts■ Blood is composed of red and white blood

cells, platelets, and plasma. Blood carries oxygen, carbon dioxide, and other sub-stances through the body.

■ Blood cell antigens determine blood groupand are important in blood transfusions.

■ Blood is carried by arteries, veins, and capillaries.

■ Blood is pushed through the vessels by theheart.

Key Concepts■ The urinary system consists of the kidneys,

ureters, the urinary bladder, and the urethra.■ The nephrons of the kidneys filter wastes

from the blood.■ The urinary system helps maintain the

homeostasis of body fluids.

Color-enhanced SEM Magnification: 120�

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992 CHAPTER 37 ASSESSMENT

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Review the Chapter 37 vocabulary words listed in the Study Guide on page 991. Distinguishbetween the vocabulary words in each pair.

1. aorta—vena cava2. artery—vein3. red blood cell—platelet4. kidney—nephron5. ureter—urethra

6. Homeostasis of blood osmotic pressure ismaintained by which organ(s)?A. lungs C. heartB. kidneys D. liver

7. Breathing is an involun-tary process controlledby which area of thebrain?A. cerebrumB. cerebellumC. medulla oblongataD. hippocampus

8. A person with Type O blood is givenType AB blood during a transfusion. Whichof the following is a possible outcome fromthe transfusion?A. The anti-A antibodies in the recipient’s

blood will attack the A antigens in thedonor’s blood.

B. The anti-B antibodies in the recipient’sblood will attack the B antigens in thedonor’s blood.

C. The donor cells will clump inside therecipient’s body.

D. all of the above

9. Emphysema is a condition that results in thedestruction of alveoli in the lungs. Whateffects would this have on the body?A. lower levels of oxygen in the bloodB. higher levels of oxygen in the bloodC. lower levels of carbon dioxide in the bloodD. no effect

10. Complete the concept map using the follow-ing vocabulary terms: aorta, arteries, leftatrium, left ventricle.

11. Open Ended A diet low in saturated fatsand cholesterol helps maintain elasticity andprevent clogging of the blood vessels. Whyis this type of diet considered healthy foryour heart?

12. Open Ended In some cities, citizens areadvised to avoid heavy outdoor exercisewhen air pollution levels are high. Explainwhy it would be wise to heed such a warning.

13. Open Ended Explain what normally hap-pens to glucose as blood passes through thekidney. Explain what happens to glucose in apatient with uncontrolled diabetes.

14. Writing About Biology When theStreptococcus bacterium that causes severesore throats gets into the blood, damage tothe valves of the heart can result. Howmight this damage affect heart function?

15. Hypertension(high blood pressure) affects more than 50 million Americans. How does hyperten-sion affect various organs of the body? Whatgroups are at risk for hypertension? Analyzethe importance of nutrition and exercise andeach of their effects on hypertension. Visit

to investigate theanswers to these questions. Make a table tohelp organize and present your findings.

REAL WORLD BIOCHALLENGE

to the

1.

2.

to the

4.

3.

Blood moves from thepulmonary vein to the

to the

DD

CC

BB

AA

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16. Design an Experiment Design an experi-ment that would test the effect of varioustypes of music on heartbeat rate. Include ahypothesis about which types of music mayraise or lower heart rate.

17. Recognize Cause and Effect Compare howthe respiratory, muscular, and nervous sys-tems interrelate to accomplish the process ofbreathing. If there were a disruption in anyone of these systems, how would it affecthomeostasis in the body?

CHAPTER 37 ASSESSMENT 993bdol.glencoe.com/standardized_test

Constructed Response/Grid InRecord your answers on your answer document.

25. Open Ended A blood test can be used to determine irregularities in many other systems ofthe body including kidney function, liver function, and respiratory efficiency. Compare howthe blood is interrelated with all other systems in the body. Include specific examples as partof your response.

26. Open Ended The bond formed between carbon monoxide and hemoglobin is over 200 times asstrong as the bond formed between oxygen and hemoglobin. Explain how exposure to carbonmonoxide can affect body homeostasis.

Multiple ChoiceUse the diagram to answer questions 18–21.

18. Which heart chamber pumpsblood to the lungs?A. 1 C. 3B. 2 D. 4

19. Where does blood go whenit leaves chamber 4?A. lungs C. right atriumB. left atrium D. aorta

20. Chamber 1 receives blood from which bloodvessel(s)?A. aorta C. pulmonary arteriesB. venae cavae D. pulmonary veins

21. Which best describes the blood in chamber 3?A. It is headed to the lungs to receive carbon

dioxide.B. It is coming from the lungs after receiving

carbon dioxide.C. It is headed to the lungs to receive oxygen.D. It is coming from the lungs after receiving

oxygen.

Study the table and answer questions 22–24.

22. Patient A has been diagnosed with acutekidney failure. Based on this information,what value could you expect his BUN to be?A. 4 mg/dL C. 26 mg/dLB. 15 mg/dL D. 35 mg/dL

23. Patient A’s kidney failure has been caused bya bacterial infection in his kidneys. Based onthis information, what value could youexpect his WBC count to be?A. 2000/�L C. 10 000/�LB. 5000/�L D. 20 000/�L

24. Patient B has healthy kidneys. Based on thisinformation, what value could you expecther BUN to be?A. 4 mg/dL C. 28 mg/dLB. 15 mg/dL D. 35 mg/dL

1

3

42

Blood Test Results

Test Normal Range Patient A Patient B

BUN 8–26 mg/dL

WBC 5000–10 000/µL 7500/µLBUN = Blood Urea Nitrogen (BUN is a measure of

the amount of urea present in the blood.)WBC = White Blood Cells

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chapter 37: respiration, circulation, and excretion · respiratory system circulatory system...

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