In humans, blood passes from the post caval to the diastolic right atrium of heart due to

Options

A. pressure difference between the post caval and atrium
B. pushing open of the venous valves suction pull
C. suction pull
D. stimulatiion of the sino auricular node

Answer

To answer the question about how blood passes from the post-caval (inferior vena cava) to the diastolic right atrium of the heart, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding the Post-Caval (Inferior Vena Cava)**:
- The post-caval refers to the inferior vena cava, which is a large vein that carries deoxygenated blood from the lower parts of the body (abdominal organs and lower limbs) back to the heart.

2. **Structure of the Heart**:
- The heart consists of four chambers: two atria (right and left) and two ventricles (right and left). The right atrium receives blood from the inferior vena cava.

3. **Diastole Phase**:
- Diastole is the phase of the cardiac cycle when the heart chambers relax. During this phase, the right atrium is in a relaxed state, allowing it to fill with blood.

4. **Pressure Difference**:
- When the right atrium is in diastole, the pressure inside the atrium decreases. This creates a pressure difference between the inferior vena cava (which has higher pressure) and the right atrium (which has lower pressure).

5. **Blood Flow Mechanism**:
- Due to this pressure difference, blood flows from the inferior vena cava into the right atrium. The flow is facilitated by the principle of fluid dynamics, where fluids move from areas of higher pressure to areas of lower pressure.

6. **Suction Pull**:
- The term "suction pull" refers to the effect of the pressure difference that helps draw the blood into the right atrium. It is not the sole reason for the blood flow but is a result of the pressure difference.

7. **Conclusion**:
- Therefore, the correct answer to the question is that blood passes from the post-caval to the diastolic right atrium of the heart due to the pressure difference between the post-caval vein and the right atrium.

### Final Answer:
The blood passes from the post-caval to the diastolic right atrium of the heart due to the pressure difference between the post-caval vein and the right atrium.

---