Sunshine StateSTANDARDSSC.F.1.3.1: The studentunderstands that livingthings are composedof major systems that function in reproduction, growth,maintenance, and regulation.SC.H.1.3.5: The studentknows that a change inone or more variablesmay alter the outcomeof an investigation.

Chapter 18: Transport and Protection 631

VOCABULARYcirculatory system p. 631blood p. 631red blood cell p. 633artery p. 635vein p. 635capillary p. 635

BEFORE, you learned

• The urinary system removeswaste

• The kidneys play a role inhomeostasis

NOW, you will learn

• How different structures of the circulatory system worktogether

• About the structure and function of blood

• What blood pressure is andwhy it is important

KEY CONCEPT

The circulatory systemtransports materials.

The circulatory system works with otherbody systems.

You have read that the systems in your body provide materials and energy. The digestive system breaks down food and nutrients, and therespiratory system provides the oxygen that cells need to release energy. Another system, called the transportsmaterials from the digestive and the respiratory systems to the cells.

Materials and wastes are carried in a fluid called . Blood moves continuously through the body, delivering oxygen and othermaterials to cells and removing carbon dioxide and other wastes from cells.

blood

circulatory system,

VOCABULARYAdd a frame game diagram for the term circulatory system to your notebook.

EXPLORE The Circulatory System

How fast does your heart beat?

PROCEDURE

Hold out your left hand with your palm facing up.

Place the first two fingers of your right handon your left wrist below your thumb. Moveyour fingertips slightly until you can feel your pulse.

Use the stopwatch to determine how manytimes your heart beats in one minute.

WHAT DO YOU THINK?• How many times did your heart beat?• What do you think you would find if you took

your pulse after exercising?

3

2

1

MATERIALSstopwatch

632 Unit 5: Human Biology

Structures in the circulatory system functiontogether.

In order to provide the essential nutrients and other materials thatyour cells need, your blood must keep moving through your body.The circulatory system, which is made up of the heart and blood vessels, allows blood to flow to all parts of the body. The circulatorysystem works with other systems to provide the body with this continuous flow of life-giving blood.

The HeartThe heart is the organ that pushes blood throughout the circulatorysystem. The human heart actually functions as two pumps—onepump on the right side and one on the left side. The right side of theheart pumps blood to the lungs to receive oxygen, and the left sidepumps blood to the entire body. The lungs receive oxygen when youinhale and remove carbon dioxide when you exhale. Inside the lungs,the respiratory system interacts with the circulatory system.

The heart is a pump moving bloodthroughout the entire body.

The Heart

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Find out more about thecirculatory system.

blood to lungs

blood from lungs

blood to lungs

blood from lungs

Which part of the heart pumps oxygen-poor blood to the lungs?Which part of the heart pumps oxygen-rich blood to the body?

The right atriumreceives oxygen-poor blood from allparts of the body.

1

The right ventriclepumps oxygen-poorblood to the lungs.

2

The left ventriclepumps oxygen-rich bloodto all parts of the body.

4

The left atriumreceives oxygen-richblood from the lungs.

3

oxygen-rich blood

oxygen-poor blood

Chapter 18: Transport and Protection 633

Each side of the heart is divided into two areas called chambers.Oxygen-poor blood, which is blood from the body with less oxygen,flows to the right side of your heart, into a filling chamber called theright atrium. With each heartbeat, blood flows from the right atriuminto a pumping chamber, the right ventricle, and then into the lungs.There the blood releases carbon dioxide waste and absorbs oxygen.

After picking up oxygen, blood is pushed back to the heart, fillinganother chamber, which is called the left atrium. Blood moves fromthe left atrium to the left ventricle, a pumping chamber, and againbegins its trip out to the rest of the body. Both oxygen-poor blood andoxygen-rich blood are red. However, oxygen-rich blood is a muchbrighter and lighter shade of red than is oxygen-poor blood. The diagram on page 632 shows oxygen-poor blood in blue, so that youcan tell where in the circulatory system oxygen-poor and oxygen-richblood are found.

Check Your Reading Summarize the way blood moves through the heart. Remember, a summary contains only the most important information.

BloodThe oxygen that your cells need in order to release energy must bepresent in blood to travel through your body. Blood is a tissuemade up of plasma, red blood cells, white blood cells, andplatelets. About 60 percent of blood is plasma, a fluid that con-tains proteins, glucose, hormones, gases, and other substancesdissolved in water.

White blood cells help your body fight infection by attack-ing disease-causing organisms. are morenumerous than white blood cells and have a different function.They pick up oxygen in the lungs and transport it throughout thebody. As red blood cells travel through the circulatory system, theydeliver oxygen to other cells.

Platelets are large cell fragments that help form blood clots when a blood vessel is injured. You know what a blood clot is if you’veobserved a cut or a scrape. The scab that forms around a cut or scrapeis made of clotted blood. After an injury such as a cut, platelets nearbybegin to enlarge and become sticky. They stick to the injured area ofthe blood vessels and release chemicals that result in blood clotting.Blood clotting keeps blood vessels from losing too much blood.

Check Your Reading What are the four components that make up blood?

Red blood cells

red blood cell

white blood cells

platelets

Blood is made mostly ofplasma, which transportsred blood cells, whiteblood cells, and platelets.

4250�

634 Unit 5: Human Biology

The circulatory system allows blood to flow continuouslythroughout the body. The runner depends on a constantflow of oxygen-rich blood to fuel his cells.

The heart pumps oxygen-poor blood tothe lungs and oxygen-rich blood to all partsof the body.

This major vein carriesoxygen-poor blood fromall parts of the body tothe heart.

oxygen-rich blood

oxygen-poor blood

In the vessels of thelungs, oxygen-poorblood becomes oxygen-rich blood.

This major artery andits branches deliver oxygen-rich blood to allparts of the body.

Circulatory System

Chapter 18: Transport and Protection 635

As blood travels through blood vessels, somefluid is lost. This fluid, called lymph, is collected inlymph vessels and returned to veins and arteries. Asyou will read in the next section, lymph and lymphvessels are associated with your immune system.Sometimes scientists refer to the lymph and lymphvessels as the lymphatic system. The lymphatic sys-tem helps you fight disease.

Blood VesselsBlood moves through a network of structures calledblood vessels. Blood vessels are tube-shaped struc-tures that are similar to flexible drinking straws. Thestructure of blood vessels suits them for particularfunctions. , which are the vessels that takeblood away from the heart, have strong walls. Anartery wall is thick and elastic and can handle thetremendous force produced when the heart pumps.

are blood vessels that carry blood back to the heart. The wallsof veins are thinner than those of arteries. However, veins are generally of greater diameter than are arteries.

Most arteries carry oxygen-rich blood away from the heart, andmost veins carry oxygen-poor blood back to the heart. However, thepulmonary blood vessels are exceptions. Oxygen-poor blood travelsthrough the two pulmonary arteries, one of which goes to each lung.The two pulmonary veins carry oxygen-rich blood from the lungs tothe heart.

Veins and arteries branch off into very narrow blood vessels calledcapillaries. connect arteries with veins. Through capillariesmaterials are exchanged between blood and tissues. Oxygen and mate-rials from nutrients move from the blood in the arteries to the body’stissues through tiny openings in the capillary walls. Waste materialsand carbon dioxide move from the tissues’ cells through the capillarywalls and into the blood in the veins.

Check Your Reading Compare and contrast arteries, veins, and capillaries.

Blood exerts pressure on blood vessels.As you have read, the contractions of the heart push blood throughblood vessels. The force produced when the heart contracts travelsthrough the blood, putting pressure on the blood vessels. This force iscalled blood pressure. Compare a vessel to a plastic bag filled with water.

Capillaries

Veins

Arteries

MAIN IDEA AND DETAILSTake notes on the mainidea. Blood exerts pres-sure on blood vessels.

Arteries, capillaries, andveins form a complex webto carry blood to all thecells in the body (30�).

636 Unit 5: Human Biology

If you push down at the center of the bag, you can see the water pushout against the sides of the bag.

The heart pushes blood in a similar way, exerting pressure on thearteries, veins, and capillaries in the circulatory system. It is importantto maintain healthy blood pressure so that materials in blood get to allparts of your body. If blood pressure is too low, some of the cells willnot get oxygen and other materials. On the other hand, if blood pres-sure is too high, the force may weaken the blood vessels and requirethe heart to work harder to push blood through the blood vessels.High blood pressure is a serious medical condition, but it can be treated.

The circulatory system can be considered as two smaller systems:one, the pulmonary system, moves blood to the lungs; the other, thesystemic system, moves blood to the rest of the body. Blood pressure ismeasured in the systemic part of the circulatory system.

You can think of blood pressure as the pressure that blood exertson the walls of your arteries at all times. Health professionals measureblood pressure indirectly with a device called a sphygmomanometer(SFIHG-moh-muh-NAHM-ih-tuhr).

Blood pressure is expressed with two numbers—one number overanother number. The first number refers to the pressure in the arterieswhen the heart contracts. The second number refers to the pressure inthe arteries when the heart relaxes and receives blood from the veins.

Blood Pressure

Blood pressure allows materials to travel to all parts ofyour body.

pressure ofblood onartery

blood flow

artery

blood flow

There are four different blood types.Each red blood cell has special proteins on its surface. Onegroup of surface proteins determines blood type. There are two blood-type proteins, A and B. A person whose blood cellshave the A proteins has type A blood. One with cells having B proteins has type B blood. Some people have both proteins—type AB blood. Other people have neither protein, a type of blood referred to as type O.

Maybe you, or someone you know, has had a blood transfusion, a procedure in which one person receives blooddonated by another. Knowing blood type is important fortransfusions. As you will learn in the next section, the body hasstructures that protect it from unknown substances. They arepart of an immune system that recognizes and protects cellsand molecules that are “self” from those that are unrecognized,or “nonself.” The body attacks unrecognized substances,including those in donated blood.

The blood used for transfusions is usually the same type as the blood type of the receiver, but sometimes other blood types are used. The diagram shows which blood types are compatible. Because the cells in type O blood have neither protein, the immune system of someone with A, B, or AB blood will not attack O blood cells. A person with type O blood, however, cannot receive any other bloodtype because that person’s immune system would attack A or Bsurface proteins.

Check Your Reading Why is it important to know your blood type?

Chapter 18: Transport and Protection 637

KEY CONCEPTS 1. What are the functions of the

two sides of the heart?

2. What is the primary functionof red blood cells?

3. Why can both high and lowblood pressure be a problem?

CRITICAL THINKING4. Apply List three examples of

the circulatory system workingwith another system in yourbody.

5. Compare and ContrastExplain why blood pressure isexpressed with two numbers.

CHALLENGE6. Identify Cause and Effect

You can feel the speed atwhich your heart is pumpingby pressing two fingers to theinside of your wrist. This isyour pulse. If you run for a fewminutes, your pulse rate isfaster for a little while, then itslows down again. Why didyour pulse rate speed up andslow down?

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Learn more about bloodtypes.

People can donate bloodto others.

Blood Type Can Donate Can ReceiveBlood To Blood From

A A, AB A, O

B B, AB B, O

AB AB A, B, AB, O

O A, B, AB, O O

Blood Type Compatibility