Your arteries and veins feed every cell in your body. If all the other tissues were suddenly removed, your friends would still recognize you; you'd look like a statue of yourself painted maroon.
Thinking of the arteries and veins as plumbing is a little simplistic; they move liquids from one place to another but the walls of the "pipes" are composed of living cells that perform useful functions throughout the system--not just at the ends. The heart is the pump for the whole system. The tissues of the heart are just as dependent on the circulatory system as are the other cells in the body.
Transporting Nutrients and Waste
The reason we die very quickly when our heart stops is that every cell needs oxygen and fuel to live, and they produce waste products that must be removed. All that stops when we have a heart attack and within seconds other organs start to die. The brain uses a great deal of energy and is one of the first organs to starve when the blood flow stops.
Transporting Oxygen and Carbon Dioxide
We think of the human body as breathing when the lungs fill with air and then contract as the air is forced out. However each cell is breathing too; every muscle cell, nerve cell, even the cells in our bones are breathing in oxygen and using it in a complicated "burning"--a biochemical reaction that produces carbon dioxide and waste (ash). Our blood bring fresh oxygen to each cell and takes away the carbon dioxide and waste products. The part of the process where are lungs fill with air is just the first step in a long sequence. The part where we breathe out is the last step.
Maintaining the Right Body Temperature
The cells of our bodies literally burn oxygen and fuel to produce heat. Some of that heat is needed for other body processes and some of it is given off to the environment. When you cuddle up to a warm person on a chilly night, you're enjoying the heat that is being transferred to their skin through their circulatory system. When you don't have someone to cuddle up with, your body will make more blood available to your skin and increase the size of the vessels in your skin so that your skin becomes warmer. If you put on more clothes, the clothes will eventually warm up and you won't need so much blood flow to the skin. Your body will shrink the vessels in the skin and redirect the blood flow to your brain if you're thinking, or to your muscles if you're working.
Circulating Hormones
Hormones are the body's public address system. When a part of the body recognizes a problem that needs the coordinated response of several body systems--perhaps running away from a snarling dog, or giving birth to a baby--hormones are produced and squirted into the blood stream to let every cell in the body know what's going on. We have hundreds of special-purpose hormones.
So now you know what your circulatory system is all about. Be sure to check out my articles on how to take care of your health and live a long and healthy life. Armed with knowledge and by taking a few steps, you will feel great!
