Copy and complete:

• The blood from the lungs enters the ______ ______. Then it gets moved down to the _______ _____. Then it gets squeezed out to the ______ _____.

• The blood from the body cells enters the _______ _______. Then it gets moved down to the _______ _______. Then it gets squeezed out to the _______.

The heart as a pump

The circulatory system

ArteryThe blood vessel that carries blood away from the heart. They have very thick walls.

thick outer wall

thick inner layer of muscle and elastic fibres

narrow central tube (lumen)

VeinThe blood vessel that takes blood into the heart. They have valves.

thin outer wall

thin inner layer of muscle and elastic fibres

wide central tube (lumen)

ValvesWhen blood is flowing against gravity, or when a vein is squeezed by muscle action, there is a risk that blood will flow in the wrong direction. Veins have valves to prevent backflow.

blood to the

heart

backflow prevented vein valve

open

vein valve closed

The heart as a pump

The three types of blood vessels

• Arteries – take the blood away from the heart. They have very thick walls.

• Veins – take the blood into the heart. They have valves.

CapillaryThe blood vessel that carries blood through the body cells. The wall is only one cell thick. They are extremely narrow and they connect the arteries to the veins.

wall only one cell thick

• Capillaries – carry blood through the body cells. The wall is only one cell thick. They are extremely narrow and they connect the arteries to the veins.

Blood vesselsvery thick wall

narrow tube

thin wall

wide tube

wall only one cell thick

ARTERY

VEIN

CAPILLARY

extremely narrow tube

Blood vessels

Compare & Contrast1. Thick walls2. Have valves3. Connect arteries to the veins4. Carry blood away from the heart5. Carry blood to and from the body cells6. Walls only one cell thick7. Thin walls8. Low pressure9. High pressure10.Carry blood into the heart