Why does your heart beat?


THAT’S THE WHY:WHEN YOU were in your mother’s womb, your heart started to beat. And it should continue to do so pretty much uninterrupted until you die.

That’s potentially billions of beats as the heart relaxes and fills with blood and then squeezes or contracts, pumping the blood to your tissues and organs.

But why does the human heart have such a rhythmic beat? That’s down to electrical signals from groups of cells in the heart called nodes – the signal spreads around and changes the chemical environment of membranes in heart muscle cells, “telling” them to contract.

The sinoatrial (SA) node near the top of the heart signals to the top chambers, called atria, to contract, and the atrioventricular (AV) node directs the signal to tell the lower chambers, or ventricles, to contract a short time later. And once the cycle is done, we (hopefully) do it all again.

If you exercise, your heart will start to beat faster in a bid to help meet the body’s extra demands for oxygen-bearing blood.

A change in blood gases alerts the brain to the need for more oxygen, then a nerve signal tells the sinus node of the heart to speed up the pumping.

And if you get a sudden fright? Again your heart rate can shoot up because the heart reacts quickly to hormones released during the “fight-or-flight” response, which activates the sympathetic nervous system and readies you for action if needed.

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