The human circulatory system, also known as the cardiovascular system, includes the heart, blood vessels and the lungs, according to LiveScience. The circulatory system transports nutrients, oxygen, hormones and other substances to cells throughout the human body.
The heart beats approximately 100,000 times per day, notes Cleveland Clinic. The organ is about the size of two human hands clasped together. Its distinctive beating sound comes from heart valves opening and closing, and each valve is approximately as wide as a half dollar. Each minute, about 1.5 gallons of blood flows through the organ. The right side of the heart pumps blood to the lungs, while the left side pumps oxygenated blood to the rest of the body.
An average human has approximately 60,000 miles of blood vessels, as LiveScience reports. The human body has enough blood vessels to wrap around the earth 2.5 times. As much as 2,000 gallons of blood flows through the body's blood vessels per day, and a normal adult contains approximately 5 to 6 quarts of blood at any given time.
Capillaries, the smallest blood vessels in the human body, make up 80 percent of the length of the circulatory system, according to LiveScience. Some capillaries are so small that they are only wide enough to allow a single red blood cell to pass through. This width comes to approximately 8 microns, which is one-tenth the width of a human hair.