Chapter 17, Section 2A Closer Look at

Blood VesselsTuesday, March 16, 2010

Pages 543 -- 547

Objectives

• Describe the functions of the arteries, capillaries, and veins.

• Identify the cause of blood pressure.

Vocabulary Words

• Coronary artery

• Diffusion

• Pressure

• Blood pressure

• sphygmomanometer

Arteries

• Blood leaving the heart travels through arteries.

• Every organ receives blood from arteries that branch off the aorta.

• The first branches are called coronary arteries.

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Coronary Arteries -- cont’d

• Other branches carry blood to the brain, intestines, and other organs.

• Each artery branches into smaller and smaller arteries.

Artery Structure

• Arterial walls are generally very thick.

• Arterial walls are made up of three layers.– EPITHELIAL: innermost

layer; smooth.– MUSCULAR: middle layer.– CONNECTIVE: outer layer;

flexible.

• Structure is both strong and flexible.

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Pulse• Your pulse is

caused by the alternating expansion and relaxation of the artery wall.

• The number of artery pulses = the number of heartbeats.

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Regulating Blood Flow

• Arterial muscles are involuntary -- they contract without your thinking about it.

• At contraction, the arterial opening becomes smaller.

• When relaxed, the arterial opening becomes larger.

• These muscles act like control gates and adjusts the amount of blood to different organs.

Capillaries• Capillaries are where materials are

exchanged between blood and the body’s cells.

• Capillary walls are one cell thick (thin).• Allows passage of oxygen and glucose

to pass easily from blood to cells. • Cellular wastes travels in the opposite

direction from cells to the blood (diffusion).

Capillaries -- cont’d

• Materials that are exchanged between the blood and the body’s cells happens through diffusion.

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Veins

• Larger blood vessels called are called veins.

• Veins carry blood back to the heart.

• Walls of the vein have three layers (like arteries with the muscle layer in the middle), but are thinner.

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Veins -- cont’d

• Factors that move blood through the veins include:– Contraction of muscles

• Example: your skeletal muscles contract and squeeze the veins in your legs.

– Larger veins have valves that prevent blood from flowing backward.

– Breathing movements exert a squeezing pressure against veins in the chest that forces blood toward the heart.

Blood Pressure

• It is the pressure that is exerted by the flow of blood against the walls of the blood vessels.

• It is caused by the force with which the ventricles contract.

• As blood moves away from the heart, the pressure decreases.

• Blood flowing through arteries exerts the highest pressure.

• Blood pressure in capillaries and veins is much lower than in arteries.

Blood Pressure -- cont’d• Blood pressure is measured by

an instrument called a sphygmomanometer.

• The first number recorded (the higher of the 2), is a measure of blood pressure while the ventricles contract and pump blood into the arteries.

• The 2nd number measures the blood pressure while the ventricles relax between heartbeats.

• Typical for a young adult is 120/80.

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Homework

• Workbook 17.2 (3/18)

• Vocabulary qui 17.2 (3/18)