Your first heart beat

[5614]

I was having a discussion earlier and wondered when a baby's first heart beat is. I think it would be at some point whilst the baby is still in the womb. But then what sets off this first beat? Is it some kind of electrical impulse, from where? Or a signal from the baby's own brain?

 

When does a baby heart beat for the first time and what initiates or stimulates this first beat to occur?

[Mokele]

Heart muscles, when developed, beat on their own. If you grow them in culture, the entire sheet of cells on the culture medium will twitch with a regular rythm. I suspect the first heart beat occurs when the development of enough muscle cells is complete to allow the twitches to synchronize and contract the whole organ.

 

Mokele

[husmusen]

I suppose it would require at least a functional nucleus for the Sino-Atrial node. Or is their some alternate means that the foetal heart uses to contract?

[Glider]

Coronary muscle cells contract autonomously, even one on its own will contract rhythmically. Their membrane has 'leaky' sodium channels so at regular intervals the membrane reaches the threshold for an action potential to occur. If several or many are put together in contact with each other, they will tend to come into phase and contract together as the AP generated by one spreads to the others.

 

The sinoatrial node is really just there for timing. It takes its input from the vagus nerve which control rate (according to demand). The atrioventricular node carries the impulse down to the apex of the heart through the bundle of His to make sure the wave of contraction starts there and moves upwards. The heart contracts in a kind of wavelike twisting or squeezing motion (the most efficient for expelling maximum volume).

 

I guess in a foetus, the 'heart' would begin to beat as soon as there were sufficient coronary cells in proximity to constitue a heart. However, there is free flow between the left and right ventricles so, whilst the foetal heart beats and moves blood at a round day 22, it's not really doing much until the coronary septum closes.