During a blood drive, Shaun noticed that the nurse punctured his vein to connect the tube for withdrawing blood. Why is blood obtained through veins and not from arteries when collecting blood?

The right answer is The pressure in veins is lower than in arteries, causing less seepage of blood.

The arteries are the vessels located at the exit of the heart towards the organs. When the heart contracts like a pump to expel the blood to the arteries, the pressure is very strong. This is called systolic pressure. To cope with this pressure, the arteries have a thick and elastic wall, to be able to stretch without breaking. The arteries have an average diameter of 2.5 centimeters, against less than 2 mm for arterioles.

Unlike the arteries, the veins are subjected to a weak pressure, since the blood starts from the organs and not from the heart. The walls of the veins are therefore thin and fairly rigid because they have little resistance to provide against the pressure. The diameter of the veins and venules is rather small (smaller than arteries) and hardly varies. Veins and venules contain about 75% of the blood. During a cut, the blood of the veins gradually trickles.

So from these explanations, we can conclude that the propositions B; C and D are false, it is rather their opposite that is right.

-Agarvated Team