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BIOL 1010 (76)
Chapter 27

BIOL 1010 Chapter 27: Topic 27.3

3 Pages

Biological Sciences
Course Code
BIOL 1010
Emily A.Mc Kinnon

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lP98729 Bio 1010 Heart rate and cardiac output depend on health and age Heart Valves Act as one-way doors at the exits of the atria and ventricles during a cardiac cycle Made of flaps of connective tissue Open when pushed from one side and closed when pushed from the other The powerfulcontractionof the ventricles forces blood against theAV valves,whichcloses them and keeps blood from flowing back into the atria The semilunar valves are pushed open when the ventricles contract. When the ventricles relax, blood in the arteries starts to flow back toward the heart, causing the flaps of the semilunar valves to close and preventing blood from flowing back into the ventricles Heart murmur Hissing sound – indicates a heart defect Occurs when a stream of blood backward through a valve Some are born with it – other have their valves damaged by infections (an example would be rheumatic fever) If surgery is needed, replacement with a synthetic valve or from an organ donor (human or animal – usually a pig) is used. During a cardiac cycle of 0.8 seconds, the atria are generally relaxed for 0.7 seconds – The SA node sets the tempo of the heartbeat
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