About Circulation

About Circulation Activity: You Gotta Have Heart

Facts at a Glance

  • The heart beats an average of 70 beats per minute.
  • That's 2.5 billion beats in a lifetime!
  • It takes 23 seconds to send blood through the body.
  • The average adult has 70,000 miles of blood vessels. If we could stretch them out end to end, they would go around the world almost three times!

    Background Information

    The circulatory system of the body consists of the heart and the blood transport system. The heart acts as a pump to force the blood through a network of tubes, called blood vessels, located throughout the whole body.

    Structure of the Heart

    The heart is almost entirely muscle. It is about the size of a clenched fist. It is located on the center line of the body, about halfway down the chest, just underneath the breast bone. It is tilted so that the lower end points toward the left. The heart is divided into four chambers. The upper two chambers are called atrium; the lower two chambers are called ventricles. The upper chambers are thin-walled and receive blood returning to the heart from the body. The lower chambers are much larger and more muscular and pump blood to the lungs and body. The left and right sides of the heart are divided by a tough wall called the septum. The blood is kept moving correctly by a series of valves between the chambers. The entire heart is surrounded by a protective layer called the pericardium, which contains a lubricating liquid.

    How the Heart Pumps The heart has a small area of specialized tissue, called the pacemaker, that gives off electrical impulses about 70 times a minute. The impulse excites heart tissue, causing it to contract. The blood flow pathway:
    1. Blood from the body enters the right atrium;
    2. Blood then moves through the valve to the right ventricle;
    3. Blood moves into the arteries of the lungs where it is oxygenated;
    4. Blood returns to the heart through the left atrium;
    5. Blood moves through the valve into the left ventricle;
    6. The left ventricle forces the blood all around the body.
    The blood vessel system is approximately 60,000 miles (96,558 km) long.
    • arteries-vessels carrying blood away from the heart.
    • arterioles-narrow arteries.
    • capillaries-the smallest blood vessels.
    • venules-narrow veins
    • veins-vessels carrying blood toward the heart.
    The Blood Your body contains about 12 pints (5-6 liters) of blood. Blood consists of four main parts:
    • Red blood cells - (erythrocytes) These are the most plentiful blood cells and are shaped like discs. Their function is to carry oxygen.
    • White blood cells - (leukocytes) White blood cells are colorless cells with no special shape. Their function is to attack and destroy germs that cause disease.
    • Platelets - (thrombocytes) Small pieces of cells, floating in the blood that help to clot the blood.
    • Plasma - This is a straw-colored liquid that carries the cells of the blood. The plasma contains chemicals such as proteins, minerals, and sugars.
    Functions of the Blood
    1. Carry oxygen to all parts of the body
    2. Carry carbon dioxide from all parts of the body to the lungs
    3. Fight infection
    4. Carry nutrients
    5. Spread out body heat
    6. Seal wounds