The Circulatory System

3. the ......and blood vessels form a completely closed and continuous system.
5. what increases in size, with less elasticity than arteries, to become the great veins that return the blood to the heart and lungs to give off carbon dioxide and repeat the cycle.
7. what controls the exits and entrances that are leak proof?
9. what does the blood pick up before returning to the heart to be pumped again round the body?
11. the blood vessels comprise of?
12. veins of the lower limbs have valves that prevent blood pooling at lower levels by?
14. is there a pulse in veins, which have thinner walls?
15. which side of the heart collect and send dark venous blood to the lungs to be purified?
16. what are the two lower chambers of the heart called?
17. what wave of expansion is felt over the muscular arteries at each beat of the heart as blood is pumped through and is usually about 74 times a minute.?

1. What are the two upper chambers of the heart called?
2. what reforms and become small veins carrying darker red blood containing waste products?
4. arteries, thick walled elastic ...... that carry freshly oxygenated blood from the heart to all parts.
6. the muscle tissue of which the heart is made is itself supplied with blood by the ...arteries.
8. what is a muscular pump divided into four chambers?
10. arteries progressively reduce in size until they form a ..... of very fine, thin walled vessels called capillaries at the point of exchange of oxygen and nutrients with the cells.
13. failure of these valves may give rise to ......veins.