Final answer:
The statement that there is enough blood in the body to fill all capillaries at the same time is false due to the enormous number of capillaries and the limited volume of blood available in the circulatory system. The correct option is false.
Step-by-step explanation:
The statement: There is enough blood in the body to fill all capillaries at the same time is false. While the human body does contain a vast network of capillaries, it does not have a volume of blood that is sufficient to fill every single one simultaneously. Capillaries are microscopic blood vessels where the exchange of water, nutrients, and waste products occurs between blood and tissues. Due to their small size and vast number, if all capillaries were to be filled at once, they would require a volume of blood far greater than what is present in the body.
Furthermore, the human circulatory system is designed for blood to flow through these vessels continuously, with the total cross-sectional area of the capillaries being much larger than the aorta. This is why the speed of flow in the capillaries is considerably reduced to allow time for efficient exchange without the blood becoming stationary, which could lead to clotting. For instance, in active muscle, there are about 200 capillaries per mm³, which translates to roughly 4 x 10⁹ capillaries for 20 kg of muscle. Considering the volume of blood needed to fill such a number of capillaries, it becomes clear that there is not enough blood in the body to simultaneously fill them all.