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

Options

A. Stimulation of the sino auricular nodes
B. pressure defference between the post caval and atrium
C. pushing open of the venous valves
D. suction pull

Explanation

To solve the question regarding how blood passes from the postcaval to the diastolic right atrium of the heart in humans, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Structures Involved**:
- The right atrium (or right auricle) is the chamber of the heart that receives deoxygenated blood.
- The postcaval vein (inferior vena cava) is one of the major veins that brings deoxygenated blood from the lower parts of the body to the right atrium.

2. **Identifying the Source of Blood**:
- The right atrium receives blood from two main veins:
- The **superior vena cava**, which carries blood from the upper body (head, neck, arms).
- The **inferior vena cava** (postcaval), which carries blood from the lower body (legs, abdomen).

3. **Understanding the Function of the Right Atrium**:
- The right atrium collects deoxygenated blood from both the superior and inferior vena cava.

4. **Understanding the Pressure Dynamics**:
- Blood flow is influenced by pressure differences. Blood moves from areas of higher pressure to areas of lower pressure.
- When the right atrium is in a diastolic state (relaxed), it has lower pressure compared to the pressure in the inferior vena cava.

5. **Conclusion**:
- The blood passes from the postcaval (inferior vena cava) to the diastolic right atrium due to the **pressure difference** between the two. Blood flows from the higher pressure in the inferior vena cava to the lower pressure in the right atrium.

### Final Answer:
Blood passes from the postcaval to the diastolic right atrium of the heart due to the pressure difference between the postcaval and the atrium.

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