Life is a Beating Heart



When we lie very still, why can we feel our heart beating, more or less, once every second?

To stay alive the laws of nature demand that your cells have a constant supply of energy which they get by breaking down glucose in the presence of oxygen.  Your body manages this supply problem by having your respiratory system put oxygen, and your gastrointestinal system put glucose (and other needed chemicals), into your blood.  But, to get enough blood to your cells, so they can have enough energy to live and work properly, your body must use energy to move it against natural forces like inertia, friction and gravity.  This job is done by your heart.

The heart is a muscular pump that provides the power needed to circulate the blood throughout your body.  It has a right and left side.  The left side pumps blood through the systemic arteries to the tissues where (by way of the capillaries) it downloads the chemicals they need (like oxygen, glucose, fats and proteins) and uploads the chemicals they don’t need (like carbon dioxide).   Then, from the capillaries, the blood returns to the right side of the heart through the systemic veins, picking up chemicals from the gastrointestinal system along the way (like carbohydrates, lipids and proteins).  The right side of your heart then pumps the blood through the pulmonary arteries to your lungs where oxygen is uploaded from the inhaled air and carbon dioxide is downloaded into the air to be exhaled.  The newly oxygenated blood then returns to the left side of your heart through the pulmonary veins and this cycle repeats itself as long as you live.

Skeletal muscle, which is attached to your bones and allows you to move around and handle things won’t work unless it’s told to do so by your nervous system.  However, your heart is unique in that it has a clump of cells in the right atrium that automatically sends out electrical signals to the rest of its muscle cells.  And similar to the wires that bring electricity into your home to power your appliances, when this natural pacemaker sends out its electrical signals, they travel along a wire-like pathway and signal your heart muscle to contract thereby powering the blood throughout your body.    

Just like an idling car needs a minimum amount of fuel to keep its engine running, so too, at complete rest your body needs a minimum amount of energy to keep its organs working.  To do this your heart must pump enough blood to meet this basic metabolic need.  Scientists think that one of the main ways your body manages this control is to have sensors within your muscles that tell your brain that you’re at complete rest and in response send out electrical signals along specific nerves.  These specific nerves then send messages to your heart by releasing molecules (neurohormones) called acetylcholine.  Like a key in a lock, acetylcholine attaches to specific (cholinergic) receptors in the pacemaker and muscle cells of your heart signaling it to beat slower and with less force, because you’re at complete rest and don’t need to use much energy.  This is how your nervous system modifies your heart’s function to go along with your body’s metabolic needs and is why when you lie still you can feel your heart beating, more or less, once every second.

Three Questions for Mr. Darwin

1)   Where did the information come from to tell my body how to make, and put together, all of the parts of my cardiovascular system, including my heart’s pacemaker and electrical wiring, and how could it have come about one step at a time since we know that all of the parts are needed for it to work properly?

2)  How did my body know how to make and put the sensors exactly where they’re needed in my muscles to inform my brain about my activity level and how do they work?

3) Where did the information come from to tell my brain how hard and fast my heart should beat when I’m asleep and how to get the job done, and how did transitional life control their heart rate without having in place all of the parts that we know are needed for it to work right?

 


Also see Dr. Glicksman's Series on

"Beyond Irreducible Complexity"

"Exercise Your Wonder"


Howard Glicksman M. D. graduated from the University of Toronto in 1978. He practiced primary care medicine for almost 25 yrs in Oakville, Ontario and Spring Hill, Florida. He now practices palliative medicine for a Hospice organization in his community. He has a special interest in how the ethos of our culture has been influenced by modern science’s understanding and promotion of what it means to be a human being.

Comments and questions are welcome.

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