Pressure in the aorta is at its lowest

Options

A. (a) just before AV valves open
B. (b) at the time of first heart sound
C. (c) at the time of second heart sound
D. (d) just before the semilunar valves open

Answer

To determine when the pressure in the aorta is at its lowest, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Cardiac Cycle**: The cardiac cycle consists of two main phases: diastole (when the heart muscle relaxes) and systole (when the heart muscle contracts). During diastole, the heart chambers fill with blood, while during systole, the heart pumps blood out.

2. **Focusing on the Left Ventricle**: The left ventricle is responsible for pumping oxygenated blood into the aorta. The pressure in the aorta is closely related to the actions of the left ventricle.

3. **Identifying the Phases of Pressure**:
- During **systole**, when the left ventricle contracts, blood is ejected into the aorta, causing the pressure to rise to its maximum, known as **systolic pressure** (approximately 120 mm Hg).
- During **diastole**, when the left ventricle relaxes, the pressure in the aorta decreases.

4. **Finding the Lowest Pressure Point**: The pressure in the aorta reaches its lowest point just before the left ventricle begins to contract again and eject blood into the aorta. This moment occurs just before the **semilunar valves** (which separate the left ventricle from the aorta) open.

5. **Defining Diastolic Pressure**: The lowest pressure in the aorta during this phase is referred to as **diastolic pressure**, which is around 80 mm Hg.

6. **Conclusion**: Therefore, the pressure in the aorta is at its lowest just before the semilunar valves open, which corresponds to the end of diastole.

### Final Answer:
The pressure in the aorta is at its lowest just before the semilunar valves open.