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Read the following passage and take notes using the Cornell Notes handout.
Blood Vessels
Blood leaving the left side of the heart is loaded with oxygen from the lungs. When it leaves the
left ventricle, the blood passes into a large blood vessel known as the aorta. The aorta is the
first of a series of blood vessels that carry the blood on its round trip through the body and back
to the heart. As blood flows through the circulatory system, it moves through three types
of blood vessels—arteries, capillaries, and veins.
Arteries Large vessels that carry blood from the heart to the tissues of the body are called
arteries. Arteries are the superhighways of the circulatory system. Except for the pulmonary
arteries, all arteries carry oxygen-rich blood. Arteries have thick walls that help them withstand
the powerful pressure produced when the heart contracts and pushes blood into the arteries.
The walls of arteries contain connective tissue, smooth muscle, and endothelium. The elastic
connective tissue allows an artery to expand under pressure. Contractions of the smooth muscle
regulate the diameter of an artery.
Capillaries The smallest of the blood vessels are the capillaries. Capillaries are the side
streets and alleys of the circulatory system. The walls of capillaries are only one cell thick, and
most are so narrow that blood cells must pass through them in single file. The real work of the
circulatory system—bringing nutrients and oxygen to the tissues and absorbing carbon dioxide
and other waste products from them—is done in the capillaries.
Veins Once blood has passed through the capillary system, it must be returned to the heart.
This is the job of the veins, which are the main streets of the circulatory system. As with
arteries, the walls of veins contain connective tissue and smooth muscle. Large veins contain
valves that keep blood moving toward the heart. Many veins are located near and between
skeletal muscles. When you exercise, contracting these muscles helps force blood through the
veins. Blood flow through the veins of the arms and legs often occurs against the force of
gravity. Exercise helps to keep blood from accumulating in the limbs and stretching the veins out
of shape. If the walls around the veins weaken from lack of activity, the valves can weaken. This
causes blood to pool in the veins, producing a condition known as varicose veins.
Text adapted from Miller, Kenneth, and Joseph Levine. Biology (2004): 946-7. Upper Saddle River, NJ: Pearson
Prentice Hall. Graphic taken from www.allrefer.com.
Winston-Salem Forsyth County Schools