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SAI International School
Subject- Biology, Class-VII
Topic- Transportation and Excretion
Subtopic- Circulatory System In Human Beings
Module- 18
Lesson notes

BLOOD VESSELS: The blood in our body flows through vessels or tubes called blood
vessels.

Blood vessels are of three main types, viz. arteries, veins and capillaries.

ARTERIES: Arteries are the blood vessels which carry blood from the heart to all the

parts of the body. Arteries carry oxygenated blood from the heart to different organs.
Pulmonary artery is an exception, because it carries deoxygenated blood from the heart

to the lungs. The arteries lie quite deep under our skin and hence they are not seen easily.

Arteries are made of thick and elastic walls. This is because blood flows through them at
high pressure. The thick and elastic walls of arteries can withstand the high pressure of

blood flowing through them.

VEINS: Veins are the blood vessels which carry blood from all the parts of the body back
to the heart. Veins are made of thinner walls. Veins carry deoxygenated blood from

different organs to the heart. Pulmonary vein is an exception, because it carries

oxygenated blood from the lungs to the heart. Veins have valves in them, which allow the
movement of blood in one direction only. The valves prevent the backflow of blood. The

greenish- blue lines that we can see just below the skin of our hands and legs are the
veins.