Depending on the individual, the human circulatory system consisting of arteries, veins, and capillaries can be between 60,000 and 100,000 miles long when laid end to end. As the circumference of the Earth is about 29,401 miles, this is enough to stretch around the Earth two to four times.
While this may seem unbelievable, it is important to note that capillaries are extremely small. They have the thickness of one, individual, epithelial cell and blood passes through them one cell at a time.
The capillaries connect the arteries to veins, the arteries carry blood away from the heart, and the veins carry blood back to the heart.