1. HUMAN BODY SYSTEMS Skeletal Muscular Circulatory Lymphatic Digestive Excretory Endocrine Reproductive Skin Respiratory

2. CIRCULATORY SYSTEM In order for the body to stay alive, each of its cells must receive a continuous supply of food and oxygen. At the same time, carbon dioxide and other materials produced by the cells must be picked up for removal from the body. This process is continually maintained by the body's circulatory system. The primary circulatory system consists of the heart and blood vessels, which together maintain a continuous flow of blood through the body delivering oxygen and nutrients to and removing carbon dioxide and waste products from peripheral tissues.

3. Blood vessels are tubes that carry blood to and from all parts of the body. The human circulatory system is made up of three types of blood vessels: arteries, veins, and capillaries. An artery is a large blood vessel with muscular tissue in the wall that carries blood away from the heart to the organs and tissues of the body. Arterioles are small branches of the artery that are about 0.2mm in diameter. The veins and smaller venules are vessels that carry blood from the organs and tissues toward the heart. Veins have small valves that open to let blood through, and close to prevent it from flowing back. Capillaries are microscopic in size. They link the arterioles and venules through a network of metarterioles.

4. The heart is a hollow pear-shaped muscular organ placed between the lungs in the middle of the chest that pumps blood through the body, supplying cells with oxygen and nutrients. The heart has four cavities: a small upper cavity (atrium) and a large lower cavity (ventricle) on each side. The adult human heart is approxi- mately the size of a fist. In an average adult, it is about five inches long and three and a half inches across at its broadest part, and it weighs less than a pound. Click here for movie

5. As blood travels through the body delivering oxygen and nutrients to the tissue, it also picks up carbon dioxide and other waste materials produced by the cells. This oxygen-poor blood is transported through a network of veins to the vena cava and to the right side of the heart, where it is then pumped into the lungs, where carbon dioxide is exhaled and the blood is replenished with oxygen. The oxygen rich blood returning from the lungs enters the left atrium, the left ventricle and into the aorta and is then distributed through the body via a network of arteries. Click on picture for blood flow with red and white blood cells

6. Blood supplies oxygen, transports nutrients, waste, and hormonal messengers to each of the sixty billion cells in the body, and defends the body against foreign material. There are close to 30 trillion blood cells in an adult. Blood has four main components: red blood cells (about 99.85%), white blood cells (about 0.15%), platelets, and liquid plasma. Since both red and white blood cells are continually being destroyed, the body must continue to produce new ones (about 2 1/2 million red blood cells every second).