Montshire Minute: Human Heart

Originally aired during the week of December 22, 2003

Monday

Your heart is an amazing pumping machine. On average, it beats 100,000 times day, when you are at work, at play, or at rest. You may be asleep, but your heart is always on the job! How does it do it? Well, your heart is one very powerful muscle. Heart muscle cells are linked by strong protein-fiber connections and electrical junctions that allow voltage to pass along easily. So contraction of one cell triggers contractions in neighboring cells, and the master pacemaker oversees it all. The pacemaker is a collection of cells called the senatorial node, which sits on top of the right atrium. Electrical signals in the two atria pump first, followed by the ventricles. For people with slow or irregular heartbeats, an artificial pacemaker is sometimes prescribed to serve as a "spark plug" for the heart.

Tuesday

Without even thinking about it, your heart contracts and relaxes, pumping blood throughout your body all the time. The heart is the center of the circulatory system, which is a complex network of veins and arteries - highways that carry blood cells in an endless stream of one-way traffic. Arteries carry oxygen-rich blood away from your heart, and veins carry oxygen-poor blood back to your heart. The tiniest of these blood vessels are capillaries. They are much thinner than a human hair, so small that red blood cells can only pass through single file. Hey, hey, no butting in line there - one at a time please! The capillaries have very thin walls that can allow the passage of oxygen and nutrients. You have about 60,000 miles of blood vessels in your body - enough to circumnavigate the glove more than two times!

Wednesday

The heart is a mighty little muscle. It weighs less than a pound and is not much bigger than your fist, but by the end of its life, it may have beat more than 3.5 billion times! Wow! With apologies to Sonny and Cher, the beat goes on! Your heart has four chambers - the upper chambers are called the left and right atria, and the lower chambers are the left and right ventricles. A wall of muscle called the septum separates the left and right atria and the left and right ventricles. The left ventricle is the largest and strongest chamber in your heart. Its chamber walls are only about a half-inch thick, but they have enough force to push blood through the aortic valve and into your body. Find out more about this amazing pumping machine in our new visiting exhibit Body Carnival: The Science and Being You on display now at the Museum.

Thursday

When you give a tennis ball a good, hard squeeze, you're using about the same amount of force your heart uses to pump blood to the body. Even at rest, heart muscles are working hard--twice as hard as the leg muscles of a sprinter! You can feel your pulse by placing two fingers at pulse points on your neck or wrists. The double beat - Lub dub, Lub dub - is from blood stopping and starting as it moves through your arteries. This "start again, stop again" action is caused by the heart valves as they open and close. If you are a kid, your resting pulse might range from 90 to 120 beats per minute. If you are a grown up, your pulse rate slows to an average of 72 beats per minute. Find out more about this amazing pumping machine in our new visiting exhibit Body Carnival: The Science and Being You on display now at the Museum.

Friday

Ok, so you gotta eat right to have a healthy heart. And you need to exercise. Health professionals will tell you that it's important to pace yourself. If you tire out too quickly, you'll never want to get on that treadmill again! Knowing your target heart rate lets you measure your fitness level and monitor your progress when you do your fitness program. So what is your target heart rate? One way to calculate it is to subtract your age from 220, and take 75% of the result. A person 30 years old would have a target heart rate of about 142 beats per minute. A new visiting exhibit at the Museum called Body Carnival includes a calculator and a pulse meter. Find out what your target heart rate is, and learn other factors that contribute to a healthy heart!