Immediately following the P wave of the electrocardiogram, an A ...

[serike]

Immediately following the P wave of the electrocardiogram, an A wave appears on both the left and right heart pressure graphs. This A wave corresponds to which of the following?
 
  a. Atrial contraction
  b. Atrioventricular valve closure
  c. Semilunar valve closure
  d. Ventricular contraction

Question 2

Opening of the semilunar valves occurs when which of the following occurs?
 
  a. The pressures in the arteries exceed those in the ventricles.
  b. The pressures in the atria exceed those in the ventricles.
  c. The pressures in the ventricles exceed those in the aorta and pulmonary artery.
  d. The pressures in the ventricles exceed those in the atria.

[vickybb89]

Answer to Question 1

ANS: A
The P wave signals atrial depolarization. Within 0.1 sec, the atria contract, causing a slight rise in both atrial and ventricular pressures (the A waves).

Answer to Question 2

ANS: C
Within 0.05 sec, ventricular pressures rise to exceed those in the aorta and pulmonary artery. This opens the semilunar valves.