Por Rossana Soletti
The origin of this complex structure
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The text below answers the question of Pedro Henrique Nagai, from São Paulo, 5 years old, for the series “Children’s questions, answers from science”.
The heartbeat has a very special symbolism: it means life, love, passion, anxiety. But when 5-year-old Pedro Henrique asks why his heart beats, the answer has to be reduced to a biological explanation.
Let’s start with the ready-made heart, and then go back to the beginning, when our body was still forming. The heart is a complex structure, a masterpiece that has four chambers: two atria, which receive blood from the body and pass it on to two ventricles, which then pump the blood into large vessels. And it produces its own impulses. Your beats are controlled by electrical signals that spread through the cells in your heart chambers. The atria contract first, then contract the ventricles, and that’s how the beat we know comes about.
We usually think of the heart as a large structure, but it is nothing more than a collection of individual cells: cardiac muscle cells form the layers of muscle; some cells help support and shape the organ; Nerve cells coordinate the heartbeat and others make up blood vessels. And it is the interaction between them all that gives the ability to pump blood to the heart, the first functional organ to be ready, even when we are an embryo. One of the biggest discoveries about its development was the realization that many of its cells are derived from the same mother cell in the first few weeks of life.
As the embryo develops, cells differentiate and specialize, in a process driven by chemical signals. Some will send signals to their neighbors, which will turn into cardiac cells, so all the precursor cells need to be in the right place at the right time. By the third week, the embryo is a three-layer sandwich and the heart begins to emerge in the middle layer from two clusters of cells that differentiate and give rise to other cell types.
In a four-week-old human embryo, the heart is a two-chambered tube that will then go through a bend. At this stage the cells already make a rhythmic contraction and there is a flow of blood, and this pressure helps the heart to bend and form the four chambers as the embryo grows. It is because of this precocious pulse that a pregnant woman can hear the baby’s heartbeat in the first weeks of pregnancy, when the embryo is still very primitive.
If we separate these contracting cardiac muscle cells and put them on a plate to be cultured in the laboratory, they can reproduce the heartbeat. If isolated on the plate, the beat of each cell is independent; when they increase in number and touch, the beat begins to be unison. This fantastic ability has been observed by scientists for over two decades and now research continues, with the aim of making these pulsating cells develop into a real heart, and to produce cardiac tissue from the transformation of other tissues of ours, like the skin, and finding explanations and treatments for various diseases.
And these conditions are not few: as we have seen, with all its complexity, once the heart is ready, everything needs to work in harmony, like an orchestra. The chambers and the passages between them must function correctly, the cells must beat at the right pace. If this does not happen, the beats may become out of sync or the required blood volume may not be pumped. That’s why cardiac alterations are among the most frequent defects in newborns, and why cardiovascular diseases are among the most common causes of death.
Scientists have been trying for centuries to understand this fantastic, complex and poetic structure, in the pursuit of greater longevity and quality of life for people.
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Rossana Soletti is a Ph.D. in morphological sciences and a professor at the Federal University of Rio Grande do Sul.
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