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

Options

A. (i) & (iv)
B. (i) & (ii)
C. (ii) & (iii)
D. (iii) & (iv)

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 (i)**: "Arteries are thick-walled and have narrow lumen as compared to veins."
- **Analysis**: This statement is correct. Arteries have thicker walls than veins due to a thicker tunica media, which is composed of smooth muscle and elastic fibers. This structure allows arteries to withstand and maintain the high pressure of blood being pumped from the heart. In contrast, veins have thinner walls and a wider lumen.
- **Conclusion**: Statement (i) is correct.

2. **Statement (ii)**: "Angina is acute chest pain when the blood circulation to the brain is reduced."
- **Analysis**: This statement is incorrect. Angina refers to chest pain caused by reduced blood flow to the heart muscle, not the brain. It typically occurs when the heart muscle doesn't get enough oxygen-rich blood.
- **Conclusion**: Statement (ii) is incorrect.

3. **Statement (iii)**: "Persons with blood group AB can donate blood to any person with any blood group under ABO system."
- **Analysis**: This statement is also incorrect. Individuals with blood group AB are known as universal recipients because they can receive blood from any blood group. However, they cannot donate blood to all groups due to the presence of A and B antigens on their red blood cells, which could cause an immune reaction in recipients with other blood types.
- **Conclusion**: Statement (iii) is incorrect.

4. **Statement (iv)**: "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 are involved in several steps of the coagulation cascade, which leads to the formation of a blood clot.
- **Conclusion**: Statement (iv) is correct.

### Final Conclusion:
The two correct statements are:
- Statement (i): "Arteries are thick-walled and have narrow lumen as compared to veins."
- Statement (iv): "Calcium ions play a very important role in blood clotting."

Thus, the correct answer is that statements (i) and (iv) are correct.