The cardiovascular system is vital to the life process of transport.

Transport is the absorption and circulation of materials like oxygen and nutrients (as well as wastes---carbon dioxide and urea) throughout the body. Important chemicals secreted by the body like hormones and antibodies are transported, as well as any chemical you put into your body such as an antibiotic or pain-killer.

This life process is important to all life forms, but how they've adapted to accomplish transport does differ. We have a heart that consists of two pumps that push blood through our blood vessels--arteries, capillaries and veins.

There are two loops that blood travels through: the pulmonary circuit carries blood from the heart to the lungs and back (picking up oxygen/dropping off carbon dioxide). The systemic circuit carries blood from the heart to the other body systems and back (dropping off oxygen/picking up carbon dioxide).

Arteries

Arteries carry oxygen-rich blood from your heart to the tissues and organs in your body, like your brain, kidneys, and liver. Blood flows through arteries with great force. So the walls of arteries are thick and flexible. The thicker walls contain an elastic protein and have smooth muscles to help protect the arteries against damage from the high pressure. Arteries get smaller and smaller as they get farther from your heart. At their smallest point, arteries become capillaries.

Capillaries

Capillaries connect arteries to veins. As the tiniest blood vessels, capillaries carry blood to and from every cell in your body. In an adult body, that means trillions of cells.

Capillary walls are so thin that oxygen and nutrients can pass right through them into your body's cells. Waste products and carbon dioxide from the cells can also pass through the walls of capillaries back into your bloodstream.

Veins

Capillaries get larger and larger as they leave body tissue and quickly become veins. Veins carry the oxygen-poor blood back to your heart. The walls of veins are much thinner than artery walls—they don't have to be as thick because blood flows through veins at a lower pressure.

Blood Components

Blood is a specialized body fluid. It has four main components: plasma, red blood cells, white blood cells, and platelets. Blood has many different functions, including:

  • transporting oxygen and nutrients to the lungs and tissues

  • forming blood clots to prevent excess blood loss

  • carrying cells and antibodies that fight infection

  • bringing waste products to the kidneys and liver, which filter and clean the blood

  • regulating body temperature

The blood that runs through the veins, arteries, and capillaries is known as whole blood, a mixture of about 55 percent plasma and 45 percent blood cells. About 7 to 8 percent of your total body weight is blood. An average-sized man has about 12 pints of blood in his body, and an average-sized woman has about nine pints.The blood that runs through the veins, arteries, and capillaries is known as whole blood, a mixture of about 55 percent plasma and 45 percent blood cells. About 7 to 8 percent of your total body weight is blood. An average-sized man has about 12 pints of blood in his body, and an average-sized woman has about nine pints.