1. The circulatory system has two divisions: a _______________circuit that serves the entire body and a _______________ circuit that functions only for gas exchange with the air inthe lungs.

2. The heart is enclosed in a fibrous, two-layered sac called the _______________.

3. The ejection of blood from the heart is regulated by the aorticand pulmonary _______________ valves.

4. The ventricles have _______________muscles and stringy _______________ to preventthe atrioventricular valves from prolapsing during ventricular systole.

5. The _______________ and_______________ veins travel through theinterventricular sulci alongside the interventricular arteries.

6. A local death of myocardium due to obstructed coronarycirculation is called _______________.

7. Compared to skeletal muscle, cardiac muscle has a relativelyscanty _______________ and therefore gets mostof its calcium ions from the _______________during contraction.

8. Unlike skeletal muscle fibers, cardiac myocytes are joined end toend by mechanical and electrical junctions called _______________.

9. Normally, each cycle of cardiac contraction is set off by itspacemaker, the _______________.

10. When this pacemaker depolarizes, we see the __________________ wave orcomplex in the electrocardiogram.

11. The action potentials of cardiac muscle exhibit a plateau,unlike those of skeletal muscle and neurons, resulting from a prolonged influx of _______________ ions.

12. The ventricles begin to relax and the second heart sound isheard at the time of the _______________ wave or complex of the electrocardiogram.

13. The contraction of any heart chamber is called _______________ and itsrelaxation is called _______________.

14. The amount of blood ejected by one contraction of a ventricle iscalled its _______________, and the percentageof its blood ejected is called its _______________.

15. Agents such as epinephrine are said to have a positive _______________ effect because they increase the heart rate and apositive _______________ effect because the increase the force of its contractions.

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