Question

The diagram given alongside represents the human heart in one phase of its functional activities. Study the same and answer the question that follow:

1. Name the phase.
2. Label the parts 1, 2 and 3.
3. Which part of the heart is contracting in this phase?
4. Draw well labelled diagram of part 1 and 2 to show the structural differences between them.

Answer 1

1. Atrial systole
2. 1: Pulmonary artery
   2: Superior vena cava
   3: Aorta
3. Atrial muscles contract during this phase because the tricuspid and bicuspid valves are open, while the semilunar valves at the roots of the pulmonary artery and aorta are closed.
4.