In humans , deoxygenated blood flows from:

Options

A. Left auricle to left ventricle during auricular systole
B. Right auricule to right ventricle during atrial systole
C. Right ventricle to aorta during ventricular systole
D. Pulmonary vein to left auricle during auricular systole

Answer

To solve the question "In humans, deoxygenated blood flows from:", we will analyze the options provided and understand the flow of blood in the human circulatory system.

### Step-by-Step Solution:

1. **Understanding Blood Flow**:
- In humans, the circulatory system consists of two main circuits: the systemic circuit (which carries oxygenated blood) and the pulmonary circuit (which carries deoxygenated blood).
- Deoxygenated blood is blood that has delivered its oxygen to the tissues and is returning to the heart to be re-oxygenated in the lungs.

2. **Identifying the Source of Deoxygenated Blood**:
- Deoxygenated blood returns to the heart through the superior and inferior vena cavae, which empty into the right atrium.

3. **Flow from Right Atrium to Right Ventricle**:
- When the right atrium contracts (during atrial systole), it pushes deoxygenated blood into the right ventricle. This is the correct pathway for deoxygenated blood.

4. **Evaluating the Options**:
- **Option 1**: Left auricle to left ventricle during atrial systole - This is incorrect because this pathway carries oxygenated blood, not deoxygenated blood.
- **Option 2**: Right auricle to right ventricle during atrial systole - This is correct as it describes the flow of deoxygenated blood.
- **Option 3**: Right ventricle to aorta during ventricular systole - This is incorrect because the right ventricle pumps blood to the pulmonary artery, not the aorta.
- **Option 4**: Pulmonary vein to left auricle during atrial systole - This is incorrect as the pulmonary veins carry oxygenated blood from the lungs to the left atrium.

5. **Conclusion**:
- The correct answer is **Option 2**: Right auricle to right ventricle during atrial systole.