Page 18 - Viva ICSE Science 5 : E-book

carry pure blood (except the lung artery which carries impure blood). Valves are absent
in arteries.

Veins

The main function of the veins is to carry oxygen-defi cit blood from diff erent parts of
the body to the heart (except the lung vein which carries oxygen-rich blood). Veins lie

closer to the surface of the skin and can be seen as greenish-blue lines in our hands and
legs. They have thinner walls than arteries. Valves are present in the veins to stop the
backward fl ow of blood as it moves towards the heart.

Capillaries

When arteries reach an organ, they branch into very fi ne tubes called capillaries.

Capillaries are extremely thin-walled (only one cell thick). The capillaries help to carry
blood to every cell of the body in order to supply it with oxygen and nutrients. When
blood leaves an organ, capillaries join together to form larger vessels which ultimately

join to form a vein.

from heart to heart

artery
capillaries

artery vein

vein

capillary

Cross-sections of blood vessels Flow of blood through the blood vessels

TIME TO REVISE

Write (T) for true and (F) for false statements.

1. There are two types of blood vessels—arteries and veins.

2. Veins carry pure blood.

3. Valves are absent in arteries.

4. Veins have thinner walls than arteries.

4