12-2 a closer look at blood web

8/9/2019 12-2 a Closer Look at Blood Web

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A Closer Look at Blood

VesselsChapter 12 Section 2


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Arteries

When blood leaves the heart,it travels through arteries

Every organ receives bloodfrom arteries that branch

off of the aortaThe first branches off the

aorta are the coronaryarteries, which carry blood

to the heart itself


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Artery Structure Walls of the artery are very thick, consisting of

3 layers

Innermost layer of the artery is smooth, madeup of epithelial tissue

Smooth surface allows blood to flow freely Middle layer of the artery consists mostly of

muscle Outer layer of the artery is made of flexible

connective tissue Artery structure gives arteries strength and

flexibility


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PulseThe pulse is caused by the alternating

expansion and relaxation of the artery wall

When the hearts ventricles contract, theysend a spurt of blood out through all thearteries in the body

This spurt travels through the arteries and

pushes the artery walls to expand Once the spurt passes, the artery walls relax

and narrow again


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Regulating Blood Flow

Muscles in the middle wall of an artery areinvoluntary muscles which contract

When these arteries contract, the openingnarrows in the artery

When the arteries relax, the opening becomeslarge

These muscles control the amount of bloodsent to different organs

More blood is sent to organs that are neededimmediately


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Capillaries Blood flows from the smallest arteries into the tiny capillaries Materials are exchanged between the blood and the bodys

cells in the capillaries Capillary walls are only one cell thick, allowing materials to

pass easily through them Oxygen and glucose pass through the capillaries Cellular waste products travel in the opposite direction; from

cells, through the capillary walls, into the blood

Materials are exchanged between the blood and the cells bydiffusion Diffusion- process by which molecules move from an area in

which they are highly concentrated to an area in which theyare less concentrated


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Veins Blood moves from the capillaries into the veins

Veins carry blood back to the heart

Veins have 3 layers, with a muscular middle layer

Veins are thinner than arteries

Many veins are located near skeletal muscles;muscle contractions help to push blood through

the veins Larger veins have valves to prevent blood from

flowing backward

Breathing movements exert a squeezing pressureagainst veins in the chest to push blood towardthe heart


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Blood Pressure

Blood pressure-pressure exerted

against the walls ofthe blood vesselscaused by the forcewith which the

ventricles contract As blood moves

further away fromthe heart, BPdecreases

Sphygmomanometermeasures BP

BP is measured in 2numbers

1st number is ameasurement of the BPwhile the left ventriclecontracts and pumpsblood into the aorta

2nd number measures theBP while the ventriclerelaxes betweenheartbeats

Healthy BP is 120/80

What Causes BP? Measuring BP
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Review Contrast the functions of arteries, capillaries, and

veins.

What causes blood pressure?

Explain the factors that enable blood in your legveins to return to the heart in spite of thedownward pull of gravity.

Arteries adjust the amount of blood flowing to

different parts of the body, depending on whereblood is needed. Use this fact to explain why itmay not be a good idea to exercise vigorouslyshortly after you eat.

12-2 a closer look at blood web

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