Question

why capillaries are thin walled

Answer 1

Firstly, you may know that caterpillar functions a great role in the environment.
They help in exchange of gases. As they bring oxygen to the tissues and remove carbon dioxide. If the caterpillars did not have thin walls, the gases could not diffuse through, it will make this important role very difficult.

Hope it help you!

Answer 2

Capillary blood vessel's walls are thin and narrow and the red blood cells can only travel through them in single file. Substances such as oxygen, carbon dioxide, nutrients and wastes are passed through the walls of the capillaries.

so, here the point is that these thin walls easily allow water, oxygen, carbon dioxide, and other nutrient and waste substances to exchange between blood cells and the surrounding tissue.

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