Tiny blood vessels where nutrients, wastes and gasses are exchanged are called?

I believe it's called capillaries.

Capillaries are exchange vessels. Gases (oxygen and carbon dioxide), nutrients, and wastes pass in both directions across capillary walls. Blood flow in capillaries is pushed by the pumping of the heart. Since water gets though cell membranes easily, the circulating blood moves water through every cell of the body.

"a.) well–developed vascular system."