Choose the correct answer from the Alternatives given
Systole refers to the contraction of:
A) Major arteries
B) SA node
C) Atria and ventricles
D) All of these

Hint: These are thin-walled chambers that receive blood from the veins and forcefully pump blood out of the heart.

Complete step -by - step answer : Systole came without change from the Greek systole which means drawing together or a contraction. The term has been in use since the 16th century to denote the contraction of heart muscle. Systole is a time period of contraction of the ventricles of the heart that occurs between the first and second heart sounds of the cardiac cycle. Systole causes ejection of blood into the aorta. Atria of the heart receive blood returning to the heart from other areas of the body. So, systole refers to contraction of atria which propels blood into ventricles and expels blood into aorta and pulmonary arteries.
Major arteries are the blood vessels of the body that carry blood away from the heart and to the organs and tissues of the body.
SA node is the major element in the cardiac conduction system, the system that controls the heart rate and this consists of the cluster of cells that are located in the upper part of the wall of the right atrium.

Thus, the correct option is C. i.e. Atria and Ventricles.

Note: Systole may also refer to the contraction stage of the contractile vacuole in protozoans. Systole is most easily assessed in isolated muscle strips where the length and systolic load can be precisely fixed and defined.