Circulatory system - a transport system for food, oxygen, and waste. It is made up of three parts: the blood, the heart, and blood vessels.

   Circulate - to follow a course that returns to the starting point

   Blood - the fluid that circulates in the heart, arteries, capillaries, and veins, carrying nourishment and oxygen and bringing away waste products from all parts of the body. The blood is made of fluid (plasma)  and solid parts (red blood cells, white blood cells, and platelets)

   Plasma is the fluid part of the blood. Usually yellowish in color and made mostly of water. Plasma makes up half our bodies.

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   Red blood cells carry oxygen to all parts of the body. They are shaped like a donut and are red because of a special chemical called hemoglobin. They always stay the same shape. There are over one hundred million (100,000,000) red blood cells in one drop of blood. Each red blood cell only lives about 120 days. Therefore, our body is constantly making new red blood cells.

   White blood cells fight off infection in our bodies. The actual color of a white blood cell is clear. They can change shape in order to squeeze through blood vessels to find bacteria and infections. There are a lot of white blood cells, but not as much as red blood cells. For every 1 white blood cell, there are about 150 red blood cells.

   Platelets are parts of cells that help control bleeding. They form together to form clots which stop the bleeding. Platelets are very small and clear. When you see them in a book or on a slide, they are often dyed with a color so that you can see them with your eye.

   Blood vessels carry blood through the body. There are three different types of blood vessels: artery, vein, capillary.

   Artery is a thick walled blood vessel that carries blood rich in food and oxygen AWAY from the heart to the body.

   Vein is a blood vessel that carries blood back to the heart from the rest of the body.

   Capillary the smallest blood vessels. They connect arteries to veins.