The blood vessels that do not have valves areveins and capillariesarteries and capillariesveins and arteriesarteries only

Break Down the Problem

1. Identify the types of blood vessels: veins, arteries, and capillaries.
2. Determine which of these have valves and which do not.

Relevant Concepts

• Veins: Usually have valves to prevent backflow of blood.
• Arteries: Do not have valves; they carry blood away from the heart under high pressure.
• Capillaries: Also do not have valves; they are small blood vessels where exchange occurs.

Analysis and Detail

1. Veins: Designed to help return blood to the heart against gravity, thus they contain valves to prevent backflow.
2. Arteries: Carry blood from the heart and do not require valves because the high pressure of blood flow keeps it moving in one direction.
3. Capillaries: These vessels connect arteries and veins and facilitate the transfer of oxygen and nutrients but do not have valves.

Verify and Summarize

After analyzing the structure and function of each type of blood vessel, it can be concluded that the vessels which do not have valves are arteries and capillaries.

Final Answer

The correct answer is: arteries and capillaries.