1. Your Heart The size of your fist Mostly muscle 4 hollow chambers
Atria (plural of Atrium)
upper chambers
Ventricles
lower chambers

2. Blood Flow Through the Heart
One way
Atria accept blood and pump it into ventricles
Weak pumps
Ventricles pump the blood out of the heart.
Much stronger
Valves force one way flow of blood

3. Circulatory System

4. Blood vessels
The blood flows through the body in a closed system from arteries to capillaries and back through veins.

5. Which is which? Why?

6. Arteries • Carry blood away from the heart to body tissue
• Most carry oxygenated blood (red)
• Thick walled to respond to blood pressure

7. Capillaries Located between arteries and veins
Gas and nutrient exchange
Functional unit of circulatory system

8. Veins Returns blood from the capillaries to the heart Thin walled
Has valves to prevent back-flow of blood

9. In your science notebook, trace a drop of blood from the heart through the body and back to the heart. Name the structures and functions along the way.