Given below are four statements (A-D) regarding human blood circulatory system
A. Arteries are thick walled and have narrow lumen as compared to veins.
B. Angina is acute chest pain when the blood circulation to the brain is reduced.
C. Persons with blood group-AB can donatc blood to any person with any blood group under ABO system.
D. Calcium ions play a very important role in blood clotting.
Which two of the above statements are correct ?

Options

A. A and D
B. A and B
C. B and C
D. C and D

Answer

To determine which two statements regarding the human blood circulatory system are correct, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement A**: "Arteries are thick walled and have narrow lumen as compared to veins."
- **Analysis**: This statement is correct. Arteries have thick walls to withstand the high pressure of blood being pumped from the heart. Their lumen (the inner open space) is narrower compared to veins, which have thinner walls and a wider lumen to accommodate the lower pressure of blood returning to the heart.

2. **Statement B**: "Angina is acute chest pain when the blood circulation to the brain is reduced."
- **Analysis**: This statement is incorrect. Angina refers to chest pain or discomfort that occurs when the heart muscle does not get enough blood (and therefore oxygen), typically due to coronary artery disease. It is not related to blood circulation to the brain.

3. **Statement C**: "Persons with blood group AB can donate blood to any person with any blood group under ABO system."
- **Analysis**: This statement is incorrect. Individuals with blood group AB are known as universal recipients, meaning they can receive blood from any ABO blood group, but they cannot donate to all groups. They can only donate to other AB individuals.

4. **Statement D**: "Calcium ions play a very important role in blood clotting."
- **Analysis**: This statement is correct. Calcium ions are essential for the blood clotting process as they help activate various coagulation factors that are necessary for forming a clot.

### Conclusion:
Based on the analysis:
- The correct statements are **A** and **D**.

### Final Answer:
The two correct statements are **A and D**.

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