As You Read

WW You’ll LearnI Compare and contrast arteries,

veins, and capillaries.I Explain how blood moves through

the heart.I ldentrfy' the functions of the

pulmonary and systemic circula-tion systems.

Vocabularyatriumventriclecoronary circulationpulmonary circulationsystemic circulationarteryveincapillary

W4? lt’s ImportantYour body’s cells depend on theblood vessels to bring nutrientsand remove wastes.

Figure 1The blood is pumped by the heart to all thecells of the body and then back to the heartthrough a network of blood vessels.

546 CHAPTER 19 Circulation

The Circulatory SystemHow Materials Move Through the Body

It’s time to get ready for school, but your younger sister istaking a long time in the shower. “Don’t use up all the water,”you shout. Water is carried throughout your house in pipes thatare part of the plumbing system. The plumbing system supplieswater for all your needs and carries away wastes. Just as youexpect water to flow when you turn on the faucet, your bodyneeds a continuous supply of oxygen and nutrients and a way toremove wastes. In a similar way materials are moved throughout

your body by your cardiovas-cular (kar dee oh VAS kyuhlur) system. It includes yourheart, kilometers of bloodvessels, and blood.

Blood vessels carry theblood to every part of yourbody, as shown in Figure 1.Blood moves oxygen andnutrients to cells and carriescarbon dioxide and otherwastes away from the cells.Sometimes the blood carriessubstances made in one partof the body to another part ofthe body where they areneeded. Movement of materi-als into and out of your cellsoccurs by diffusion (dihFYEW zhun) and active trans—port. Diffusion occurs when amaterial moves from an areawhere there is more of it to anarea where there is less of it.Active transport is the oppo-site of diffusion. Active trans-port requires energy, butdiffusion does not.

The HeartYour heart is an organ made of cardiac muscle tissue. It is

located behind your breastbone, called the sternum, andbetween your lungs. Your heart has four compartments called

chambers. The two upper chambers are called the right and leftatriums (AY tree umz). The two lower chambers are called theright and left ventricles (VEN trih kulz). During one heartbeat,both atriums contract at the same time. Then, both ventriclescontract at the same time. A one-way valve separates eachatrium from the ventricle below it. The blood flows only in onedirection from an atrium to a ventricle, then from a ventricleinto a blood vessel. A wall prevents blood from flowing betweenthe two atriums or the two ventricles. This wall keeps blood richin oxygen separate from blood low in oxygen. If oxygen-richblood and oxygen—poor blood were to mix, your body’s cellswould not get all the oxygen they need.

Scientists have divided the circulatory system into three sec-tions—coronary circulation, pulmonary (PUL muh ner ee) cir—culation, and systemic circulation. The beating of your heartcontrols blood flow through each section.

Coronary“ Circulation Your heart has its own blood vesselsthat supply it with nutrients and oxygen and remove wastes.Coronary (KOR uh ner ee) circulation, as shown in Figure 2, isthe flow of blood to and from the tissues of the heart. When thecoronary circulation is blocked, oxygen and nutrients cannotreach all the cells of the heart. This can result in a heart attack.

AortaCoronary[arteries

Figure 2

Coronaryveins

AT H0416

[—lnfflringHow Hard

the Heart WorksProcedure fl1. Make a fist and observe its

size, which is approximatelythe size of your heart.

. Place your fist in a bowl ofwater. Then clench andunclench your fist to causewater to squirt out betweenyour thumb and forefinger.

. Continue the squeezingaction for 3 min. Determinethe number ofsqueezes perminute.

Analysis1. How many times did you

squeeze your fist in l min?A resting heart beatsapproximately 70 timesper minute.

. What can you do when themuscles ofyour hand andarm get tired? Explain whycardiac muscle cannot dothe same.

Like the rest of the body, the heart receives theoxygen and nutrients that it needs from the blood.The blood also carries away wastes from the heart’scells. On the diagram, you can see the coronaryarteries, which nourish the heart.

547SECTION 1 The Circulatory System

Oxygen—rich blood travels from thelungs through the pulmonary vein andinto the left atrium. The pulmonaryveins are the only veins that carryoxygen-rich blood.

a Blood, high in carbon dioxideand low in oxygen, returns from thebody to the heart. It enters the rightatrium through the superior and Superior

vena cava Aortainferior vena cavae.

Capillaries

Pulmonary artery

Pulmonary vein/ Left atrium

Right atrium

Left Leftlung vena cava ventricle ventricle lungRight Inferior Right

In The left atrium contracts and forcesthe blood into the left ventricle. The leftventricle contracts, forcing the bloodout of the heart and into the aorta.

B The right atrium contracts, forcing the bloodinto the right ventricle. When the right ventriclecontracts, the blood leaves the heart and goesthrough the pulmonary artery to the lungs. Thepulmonary arteries are the only arteries that carryblood that is high in carbon dioxide.

Figure3 _ _ , r-vculation The flow of blood through thePU'monaryCirCU'ationmOVes heart to the lungs and back to the heart is pulmonaryblOOd bEtween the heart c1r'culation. Use Figure 3 to trace the path blood takes througharid ll"‘95- this part of the circulatory system. The blood returning from the

body through the right side of the heart and to the lungs con—tains cellular wastes. The wastes include molecules of carbondioxide and other substances. In the lungs, gaseous wastes diffuseout of the blood, and oxygen diffuses into the blood. Then theblood returns to the left side of the heart. In the final step of pul-monary circulation, the oxygen—rich blood is pumped from theleft ventricle into the aorta (ay OR tuh), the largest artery in yourbody. Next, the oxygen—rich blood flows to all parts of your body-

of th e major arteriese systemic circulation

In your heart in the arteries

(YAR tuh reez) and veins (VAYNZ)System. Oxygen-HCh blood flows froOfthis system, Then nutrients and OXY .gen are d 1t0 YouIf bOdY cells and exChanged for carbon aenddbywablstOOd8 es.Finally’ the b1.00d returns to Y0ur heart in '

c circulation system. the vems 0f the SYS-temi

a Readlng ChECk Whatare the functions ofthe systemic circulationsystem in yourbody?

Figure 4The rate at which blood flows through the

systemic circulation system depends on

how quickly the left ventricle contracts.

Aorta How does the rate change when a person

has beenjumping rope?

iE Carotid arteryInternal

jugular vein

Superl'orvenacava Heart

Inferior I I)l;vena cava ,1"

j; /{ i/ ,

'r(.

Connectivetissue\

Smooth muscle

Elastic connective tissue

Smooth lining

Artery

Figure 5The structures ofa arteries,[3 veins, and capillaries aredifferent. Valves in veins preventblood from flowing backward.Capillaries are much smaller.Capillary walls are only onecell thick.

Connective

Blood Vessels

Elastic connective

tissue

CapillaryVein

In the middle 16005, scientists proved that blood moves m' L.one direction in a blood vessel, like traffic on a one—way street. _.They discovered that blood moves by the pumping of the heart ,and flows from arteries to veins. But, they couldn’t explain how ‘blood gets from arteries to veins. Using a new invention of thattime, the microscope, scientists discovered capillaries (KAP uh -‘ler eez), the connection between arteries and veins. '

Arteries As blood is pumped out of the heart, it travels :through arteries, capillaries, and then veins. Arteries are blood "'vessels that carry blood away from the heart. Arteries, shown inFigure 5A, have thick, elastic walls made of connective tissue andsmooth muscle tissue. Each ventricle of the heart is connected toan artery. The right ventricle is connected to the pulmonary fartery, and the left ventricle is attached to the aorta. Every time _your heart contracts, blood is moved from your heart into arteries.

Veins The blood vessels that carry blood back to the heart arecalled vem's, as shown in Figure SB. Veins have one-way valvesthat keep blood moving toward the heart. If blood flows back— -‘-ward, the pressure of the blood against the valves causes them toclose. The flow of blood in veins also is helped by your skeletalmuscles. When skeletal muscles contract, the veins in these mus-cles are squeezed and help blood move toward the heart. Twomajor veins return blood from your body to your heart. Thesuperior vena cava returns blood from your head and neck.Blood from your abdomen and lower body returns through theinferior vena cava.

a Reading Check What are the similarities and differencesbetween arteries and veins?

w—vuva-

.— INTEGRATION

capmaries Arteries and veins are connected by microscopicblood Vessels called capillaries, as shown in Figure 5C. The wallsof capillaries are only one cell thick. You can see capillaries when

ou have a bIOOdShOt eye They are the tiny red lines you see inthe white area of your eye. Nutrients and oxygen diffuse intobody cells through the thin capillary walls. Waste materials andcarbon dioxide diffuse from body cells into the capillaries.

Blood Pressure'9" Physics If you fill a balloon with water and

then push on it, the pressure movesthrough the water in all directions, as

shown in Figure 6. Your circulatory system is like the water bal-loon. When your heart pumps blood through the circulatorysystem, the pressure of the push moves through the blood. Theforce of the blood on the walls of the blood vessels is calledblood pressure. This pressure is highest in arteries and lowest inveins. When you take your pulse, you can feel the waves of pres—sure. This rise and fall of pressure occurs with each heartbeat.Normal resting pulse rates are 60 to 100 heartbeats per minutefor adults, and 80 to 100 beats per minute for children.

Measuring Blood Pressure Blood pressure is measured inlarge arteries and is expressed by two numbers, such as 120 over80. The first number is a measure of the pressure caused whenthe ventricles contract and blood is pushed out of the heart.This is called the systolic (sihs TAHL ihk) pressure. Then, bloodpressure drops as the ventricles relax. The second number is ameasure of the diastolic (di uh STAHL ihk)pressure that occurs as the ventricles fill withblood just before they contract again.

Controlling Blood Pressure Your bodytries to keep blood pressure normal. Specialnerve cells in the walls of some arteries sensechanges in blood pressure. When pressure ishigher or lower than normal, messages are sentto your brain by these nerve cells. Then messagesare sent by your brain to raise or lower bloodpressure—by speeding up or slowing the heartrate for example. This helps keep blood pressureconstant within your arteries. When blood pres-sure is constant, enough blood reaches all organsand tissues in your body and delivers needednutrients to every cell.

>~S*5 INTEGRATION

Some molecules of nutn'-ents are forced throughcapill'ary walls by the forceof blood pressure. What Is'the cause of the pressure?Discuss your answer mma classmate. Then wn'teyour answer m' yourScience Journal.

Figure 6When pressure is exerted on afluid in a closed container, thepressure is transmitted throughthe liquid in all directions. Yourcirculatory system is like a closedcontainer.

Water—filledballoon

NATIONALGEOGRAPHIC ISUALIZING ATHEROSCLEROSIS

Figure 7

ealthy blood vessels have smooth,H unobstructed interiors like the one

at the right. Atherosclerosis is adisease in which fatty substances build upin the walls of arteries, such as the coro-nary arteries that supply the heart musclewith oxygen-rich blood. As illustratedbelow, these fatty deposits can graduallyrestrict—and ultimately block—the life-giving river of blood that flows throughan artery.

Vessel Wall

Vessel Wall

b NEARLY BLOCKED ARTERY In theillustration and photo at right, fattydeposits have continued to build. Thepathway through the coronary arteryhas gradually narrowed until bloodflow is very slow and nearly blocked.Under these conditions, the heartmuscle cells supplied by the artery aregreatly weakened. lf blood flow stopsentirely, a heart attack will result.

Vessel l’.

Platelet

Red blood cm.

A HEALTHY ARTERY The illustration and photoabove show a normal functioning artery.

{ PARTIALLY (LOGGED ARTERY The illus-tration and inset photo at left show fattydeposits, called plaques, that have formedalong the artery’s inner wall. As the dia-gram illustrates, plaques narrow the path-way through the artery, restricting andslowing blood flow. As blood supply to theheart muscle cells dwindles, they becomestarved for oxygen and nutrients.

“1.3.”? V 1:; v '

I cardiovascular Disease

Any disease that affects the cardiovascular system—theheart, blood vessels, and blood—can seriously affect the health

- ofyour entire body. People often think of cancer and automo—bfle accidents as the leading causes of death in the United States.

- However, heart disease is the leading cause of death.

, Atherosclerosis One leading cause of heart disease is calledatherosclerosis (ah thur oh skluh ROH sus). In this condition,

_‘ shown in Figure 7, fatty deposits build up on arterial walls. Eatingfoods high in cholesterol and saturated fats can cause these

i_ deposits to form. Atherosclerosis can occur in any artery in the_' body, but deposits in coronary arteries are especially serious. If a. coronary artery is blocked, a heart attack can occur. Open heart" surgery may then be needed to correct the problem.

,1 Hypertension Another condition of the cardiovascular sys-tem is called hypertension (HI pur ten chun), or high bloodpressure. Figure 8 shows the instruments used to measure

,_ blood pressure. When blood pressure is higher than normalI most of the time, extra strain is placed on the heart. The heartI must work harder to keep blood flowing. One cause of hyper-

: tension is atherosclerosis. A clogged artery can increase pres—sure within the vessel. The walls become stiff and hard, like ametal pipe. The artery walls no longer contract and dilate easilybecause they have lost their elasticity.

- Heart Failure Heart failure‘ results when the heart cannot

. pump blood efficiently. It might1 be caused when heart muscle tis—" sue is weakened by disease or

when heart valves do not work- properly. When the heart does not

' pump blood properly, fluids col-“ lect in the arms, legs, and lungs.

People with heart failure usuallyare short of breath and tired.

Z, Reading Check Whatisheartfailure?

. Figure 8.i Blood pressure is measured in large

. arteries using a blood pressure cuff; and stethoscope.

. ' ’

mac! ‘ "v

Research Visit theGlencoe Science Web site atscience.glencoe.com forrecent news or magazinearticles about cardiovasculardisease. Write a paragraph inyour Science Journal aboutsteps you can take to lead ahealthy lifestyle.

Preventing CardiovascuiDisease Having a healthy lifesis important for the health of yo,cardiovascular system. The choiceyou make to maintain good healtmay reduce your risk of future serious.illness. Regular checkups, a healthfuldiet, and exercise are part of a heart- ~healthy lifestyle. i

Many diseases, including cardio-vascular disease, can be prevented by.following a good diet. Choose foods ‘that are low in salt, sugar, cholesterol, ‘and saturated fats. Being overweightis associated with heart disease and'

Figure 9 high blood pressure. Large amounts of body fat force the heartNicotine, present in tobacco, con— to pump faster.tracts blood vessels and causes the Learning to relax and having a regular program of exercise;bOdyto mleasemrmonesmat can help prevent tension and relieve stress. Exercise alsoraise “00" Pressure ' strengthens the heart and lungs, helps in controlling cholesterol, '-

tones muscles, and helps lower blood pressure. IAnother way to prevent cardiovascular disease is to not

smoke. Smoking causes blood vessels to contract, as shown m:Figure 9, and makes the heart beat faster and harder. Smoking'also increases carbon monoxide levels in the blood. Not smok—ing helps prevent heart disease and a number of respiratory sys-tem problems, too.

Assessment

Skill Builder Activities1. Compare and contrast the structure of thethree types of blood vessels.

2. Explain the pathway of blood throughthe heart.

3. Contrast pulmonary and systemiccirculation. Identify which vessels carryoxgen—rich blood.

6. Concept Mapping Make an events chain con—cept map to show pulmonary circulationbeginning at the right atrium and ending atthe aorta. For more help, refer to the ScienceSkill Handbook.

7. Using a Database Research diseases of the cir-culatory system. Make a database showing whatpart ofthe circulatory system is affected by each

5. Think Criticany What waste product disease. Categories should include the organs andbuilds up in blood and cells when the heart VESSEIS 0fthe CerUlatorY SYStem- For more he'P:is uname to pump brood efficienfly? refer to the Technology Skill Handbook.

4. Explain how exercise can help preventheart disease.