58. Blood collection tubes fill correctly during venipuncture due to which of the following factors?
Answer: D
Blood collection tubes fill correctly during venipuncture due to the negative pressure within the tube.
The negative pressure within the tube is what allows blood to flow into it during venipuncture. This pressure differential draws the blood into the tube once the needle is inserted into the vein.
A) The high pressure in the arterial system
This option is incorrect because the arterial system operates at a much higher pressure than the venous system. During venipuncture, the focus is on venous access, not arterial, and the filling of tubes relies on the pressure differential, not the high pressure of arteries.
B) The high pressure in the venous system
While the venous system does contain blood under pressure, it is not significantly high compared to the arterial system. This option is misleading because the filling of the tubes is not primarily driven by venous pressure; rather, it is the negative pressure in the collection tubes that facilitates the filling process.
C) The positive pressure created by the tourniquet
This choice is incorrect as the tourniquet is used to temporarily occlude blood flow, which might increase pressure in the veins slightly but does not create the filling mechanism for the tubes. The actual filling of the tubes occurs due to the negative pressure inside them, not from any positive pressure created by the tourniquet.
D) The negative pressure within the tube
This option is correct as it directly describes the mechanism by which blood collection tubes fill. The negative pressure inside the tube creates a vacuum effect that draws the blood from the vein into the tube during venipuncture.
Conclusion
The correct answer is D, as the negative pressure within the collection tube is essential for drawing blood during venipuncture. All other options fail to accurately describe the mechanism of tube filling, either misrepresenting the role of pressure in the venous system or misunderstanding the function of the tourniquet. Understanding these dynamics is crucial for effective blood collection procedures.