With reference to the blood in a normal person, which one of the following statements is correct?
A
Compared to arteries, veins are less numerous and hold less of the body's blood at any given time
B
Blood cells constitute about 70 per cent of the total volume of the blood
C
White Blood Cells (WBC) are made by lymph nodes only
D
The blood has more platelets than WBC
Correct Answer: Option D
Explanation
1. The question asks for the correct statement about blood in a normal person.
2. Statement A is incorrect. Veins are generally more numerous than arteries and hold a larger volume of the body's blood (about 60-70%) at any given time, acting as a reservoir.
3. Statement B is incorrect. Blood cells (red blood cells, white blood cells, platelets) constitute about 40-45% of the total blood volume (this percentage is called hematocrit); the rest is plasma.
4. Statement C is incorrect. White Blood Cells (WBC) are produced primarily in the bone marrow, although some types mature or proliferate in lymph nodes and other lymphoid tissues.
5. Statement D is correct. In a normal person, the concentration of platelets (thrombocytes) in the blood (typically 150,000-400,000 per microliter) is significantly higher than that of White Blood Cells (WBC) (typically 4,000-11,000 per microliter).